Anisocoria is a condition in which the pupils of the right and left eyes differ in size or diameter. The pupil is the circular black area in the center of the iris. Depending on the lighting it can have dimensions from 1mm to 6mm in diameter.

In the presence of general or ocular pathology, anisocoria is always combined with the following manifestations:

• restriction of eye movement, or an eye with a larger pupil
• drooping of the upper eyelid (ptosis)
• pain in the eyes
• fever or fever
• headache
• decreased vision
• double vision

Causes of anisocoria

There are two types of anisocoria:

• physiological. Normally, every fifth person has a slight difference in pupil size.
• pathological. Eye diseases that can lead to anisocria: glaucoma, inflammatory eye diseases (iritis, uveitis), eye tumors
• pathological in case of general human diseases: viral infection, syphilis, brain tumors, cranial nerve palsy, Horner's syndrome, migraine, cerebral aneurysm.

When should I see a doctor urgently?

Anisocoria can be a sign of a very serious medical condition that requires urgent medical attention.

Therefore, see your doctor if you have any of the following symptoms:

• temperature rise
• strong headache
• nausea and dizziness
• double vision
• drooping and swelling of the upper eyelid

If you have a head injury and the pupils of the eyes have become of different sizes, be sure to consult a doctor.

How to treat anisocoria

Physiological anisocoria does not affect vision and eye health and therefore does not need treatment.

With pathological anisocoria, the cause of the appearance of different pupils is first identified. Then treatment is carried out.

For example, a brain infection is treated in a specialized hospital. Prescribe a course of antibiotics and antiviral drugs.

Head tumors and head aneurysms require surgical treatment.

With glaucoma, treatment is carried out aimed at normalizing eye pressure and preventing the development of glaucoma attacks.

For inflammatory diseases of the eye, a course of antibiotic treatment is carried out.

For eye tumors, surgical treatment is indicated.

What absolutely should not be done with anisocoria

When a symptom of different pupils appears, you should not:

• instill drops on your own, which can affect the size of the pupils

What happens if the symptom of anisocoria is not treated

In the case of physiological anisocoria, treatment of the symptom is not required.

The presence of pathological anisocoria indicates serious eye or head disease. Therefore, if the cause is not identified and treatment is started on time, serious complications and the development of conditions that threaten the patient's life may develop.

Prevention of anisocoria

There are no specific measures for the prevention of anisocoria. However, you can reduce your risk of developing this condition by using protective equipment when practicing contact sports.

Procedure LASIK or Lasik (in situ laser keratomileusis), commonly referred to simply as laser vision correction, is a type of refractive surgery for the treatment of myopia, hyperopia and astigmatism. LASIK is performed by an ophthalmologist using a laser. A laser is used to reshape the cornea to improve visual acuity (clarity and sharpness of the visible image). LASIK surgery is similar to other surgical corrective procedures such as Photorefractive Keratectomy (PRK) (also called UPA - Advanced Superficial Ablation). Side effects include halos, flares, trouble driving at night, and dry eyes. LASIK and PRK are more advanced than radial keratotomy in the surgical treatment of refractive error of vision. For patients with moderate to severe myopia or thin corneas who cannot be treated with LASIK, artificial lens implantation remains a popular alternative. Thus, for some patients, LASIK is an alternative to glasses or.

History of LASIK laser correction

Barracker's early work

In the 1950s, Spanish ophthalmologist José Barraquer developed in Bogotá, Colombia, the microkeratome and keratomileusis techniques. In his hospital, he cut off thin (one-hundredth of a millimeter thick) flaps of the cornea to reshape it. Barracker also investigated how much corneal volume should be left unchanged for stable long-term results. This work was followed by the work of the Russian scientist, Svyatoslav Fedorov (1920-2000), who developed radial keratotomy (RC) in the 1970s and created the first implantable contact lenses for the posterior chamber (implantable artificial lens) in the 1980s.

Medical laser

In 1968 at the Northrop Corporation Research and Technology Center at the University of California, USA, Mani Lel Bhaumik developed a carbon dioxide laser. This was the beginning of the excimer laser, the cornerstone of laser eye surgery. In May 1973, a meeting of the Denver Optical Society of America took place in Denver, Colorado, USA, where Bhaumik announced his success with the laser. Later he patented his invention.

Medical laser application in refractive surgery

In 1980, Rangaswami Srinivasan at an IBM research laboratory discovered that an ultraviolet excimer laser could etch living tissue with precision and without thermal damage to the surrounding space. He called this phenomenon "ablative photodegradation" (PRD). Five years later, in 1985, Stephen Trockel of the Edward S. Harkness Eye Institute at Columbia University in New York published his work using an excimer laser in radial keratotomy. He wrote:

“The central flattening of the cornea, obtained through radial cuts with diamond scalpels, was duplicated with radial laser cuts in 18 enucleated human eyes. The incisions made with 193 nm far-ultraviolet light emitted by an excimer laser flattened the cornea in the range of 0.12 to 5.35 diopters. Both the depth of the incisions in the cornea and the degree of flattening of the cornea are related to the applied laser energy. Histopathology revealed unusually smooth edges of the laser incisions. "

Together with his colleagues, Charles Mannerlin and Terry Clapham, Trockel founded VISX USA inc. In 1989, MD Marguerite B. McDonald performed the first VISX refractive human eye surgery.

Implementation of LASIK vision correction procedure

Patent

On June 20, 1989, Golem A. Payman received a US patent for the LASIK operation (US4840175). It was like this:

“Method and apparatus for changing the curvature of the living cornea using an excimer laser. A thin layer is removed from the living cornea, after which the exposed inner surface is left. Then the surface or thin layer is subjected to a laser beam treatment along a predetermined sample to remove the desired parts. The thin layer is then returned to the surface. Clipping the central surface area or thin layer makes the cornea less curved, while removing the annular area extending from the center of the surface or layer increases the curvature of the cornea. The desired target pattern is formed using an adjustable diaphragm, a variable size rotating aperture, a movable mirror, or a movable fiber optic cable through which the laser beam is directed to an exposed inner surface or a clipped thin layer. "

Execution in the USA

The LASIK technique was implemented in the USA after being successfully applied elsewhere. The US Food and Drug Administration (FDA) has begun testing an excimer laser. Summit Technology was the first company to receive approval for the use of an excimer laser for photorefractive keratectomy. In 1992, under the direction of the FDA, Pallikaris introduced the LASIK technique at ten VISX centers. In 1998, the Kremer Excimer Laser, serial number KEA 940202, was approved by the FDA for exclusive use in LASIK surgery. Summit Technology subsequently became the first company to receive FDA approval for the mass production and distribution of excimer lasers. This was followed by VISX and other companies.

Pallikaris suggested that the corneal flap could be lifted with a microkeratome prior to PRK with an excimer laser. The addition of a flap to PRK has become known as LASIK laser vision correction.

Further developments of LASIK

Since 1991, further developments have followed, such as faster lasers; larger contact spots; no scalpel flap excision; intraoperative corneal pachymetry; methods "with wavefront optimization" and "with wavefront control". However, the use of an excimer laser carries the risk of damage to the retina and optic nerve. The goal of refractive surgery is to avoid permanent weakening of the cornea by incisions and less energy to the surrounding tissue.

Experimental Methods

• "Simple" LASIK operation: LASEK, Epi-LASIK;
• Bowman's sublayer keratomileusis (LASIK with a thin flap);
• PRK with wavefront control;
• Advanced Artificial Lens;
• Femtosecond laser intrastromal vision correction: using femtosecond correction, for example, femtosecond lens extraction, FLIVC or "IntraCOR");
• Keraflex: a thermobiochemical solution marked "CE" for refractive correction, undergoing European clinical trials for the correction of myopia and keratoconus;
• Technolas FEMTEC laser: IntraCOR ablation without incisions for senile myopia; undergoes clinical trials to correct other conditions of myopia.

Procedure process

The procedure involves creating a thin flap over the eye, folding it to reconstruct tissue underneath with a laser and moving it into place.

Preoperative procedures

Contact lenses

Patients wearing soft contact lenses are asked to stop wearing them 5-21 days before surgery. One industry organization recommends that patients who wear hard contact lenses stop wearing at least six weeks, plus an additional six weeks every three years that hard contact lenses are worn. The cornea is devoid of blood vessels because it must be transparent to function properly. Her cells absorb oxygen from the tear film. Thus, contact lenses with low oxygen permeability reduce the uptake of oxygen by the cornea, which sometimes leads to the formation of new blood vessels in the cornea.

This causes a slight increase in the duration of inflammation and healing time, as well as some pain during surgery due to more bleeding. Although some contact lenses (especially modern rigid gas permeable and soft silicone hydrogel lenses) are made of materials with greater oxygen permeability, which helps to reduce the risk of new corneal vessel formation. Patients considering LASIK surgery are cautioned to avoid over-wearing contact lenses. It is generally recommended that they stop wearing contact lenses a few days or weeks prior to LASIK laser vision correction.

Preoperative examination and preparation

In the US, the FDA has approved LASIK for ages 18 and older. More importantly, the patient's eye prescription should not be changed for at least one year prior to surgery. Before the procedure, the patient may be examined with pupil dilation and informed. Before the operation, the patient's cornea is examined with a pachymeter to determine the thickness and with a topographer, a corneal topography machine to measure the surface contour. Using low power lasers, the topographer creates a topographic map of the cornea. The procedure is contraindicated if the topographer finds complications such as keratoconus. In the preparatory process, astigmatism and other abnormalities in the shape of the cornea are also diagnosed. Using this information, the surgeon calculates the volume and location of the corneal tissue to be removed. The patient is prescribed an antibiotic in advance for self-administration to minimize the risk of infection after the procedure, and a short-acting oral sedative is sometimes offered as a medication. Anesthetic eye drops are administered before the procedure.

Operation

Flap creation

A soft corneal suction ring is applied to the eye, keeping the eye in place. This step in the procedure can sometimes rupture small blood vessels, resulting in bleeding or subconjunctival hemorrhage into the white (sclera) of the eye. This safe side effect goes away within a few weeks. Increased absorption causes transient blurred vision in the treated eye. When the eye is immobilized, a flap is created. This process is accomplished with a mechanical microkeratome using a metal blade or a femtosecond laser that creates a series of tiny, closely spaced vesicles in the cornea. A rod is left at one end of the flap. The flap folds down to expose the stroma, the middle layer of the cornea. Lifting and folding the flap can sometimes be awkward.

Laser correction

The second stage of the procedure uses an excimer laser (193 nm) to reconstruct the corneal stroma. The laser vaporizes tissue in a precisely controlled manner without damaging the adjacent stroma. No heat burnout or actual clipping is required for tissue ablation. The layers of tissue removed are one tenth of a micrometer thick. Carrying out laser ablation in the deeper corneal stroma provides faster vision recovery and less pain than the earlier technique, photorefractive keratectomy (PRK). During the second stage, the patient's vision becomes blurry when the flap is lifted. The patient can only see the white light surrounding the orange laser light, which can lead to mild disorientation. The excimer laser uses an eye-tracking system that follows the position of the patient's eye up to 4000 times per second, changing the direction of the laser pulses in the treatment area. A typical pulse is about 1 millijoule (mJ) of pulse energy at 10-20 nanoseconds.

Moving the flap

After laser reshaping of the stromal layer, the LASIK flap is carefully moved over the treatment area by the surgeon and checked for air bubbles, foreign bodies and proper fit over the eye. The flap remains in place by natural adhesion until healing is complete.

Post-operative care

Patients are usually prescribed a course of antibiotic and anti-inflammatory eye drops. They continue to be taken for several weeks after the operation. Patients are advised to rest and are given a pair of tinted eye patches to protect the eyes from bright light and safety glasses to prevent eye rubbing during sleep and reduce dry eyes. They are also required to moisturize their eyes with preservative-free artificial tears and follow the instructions for administering the drops prescribed. Patients should be adequately informed by their surgeon about the importance of proper postoperative care to minimize the risk of complications.

LASIK with wavefront control

Wavefront controlled LASIK is a variation of LASIK in which, instead of applying a simple correction of the focusing force to the cornea (as in the traditional LASIK procedure), the ophthalmologist applies a spatially variable correction by directing a computer controlled excimer laser with measurements from a wavefront sensor. The goal is to achieve a more ideal eye from an optical point of view, although the final result still depends on the clinician's success in predicting changes that occur during healing and other factors that may relate to the uniformity / irregularity of the cornea and the axis of any residual astigmatism. In older patients, scattering from microscopic particles (cataract or incipient cataract) may play a role that outweighs any benefit from wavefront correction. Therefore, patients who expect so-called "super vision" from such procedures may be disappointed.

Australian ophthalmologist Noel Elpins, who developed a vector analysis method to analyze astigmatism in cataract, refraction and corneal surgery, has long advocated combining vector planning with wavefront controlled LASIK. Elpins argued that the purely refractive approach presented by wavefront analysis contradicts long-term experience with corneal surgery. Refractive surgeons have long known that corneal uniformity is the basis for superior vision results. Since refractive and corneal topographic astigmatism does not always align, correction of internal optical errors surgically sculpted on the cornea can increase corneal irregularity.

Elpins believes that the path to "super vision" requires more individual reduction in corneal astigmatism than is usually done, and that any residual astigmatism should be uniform (as opposed to uneven). These are the basic principles of vector planning that are overlooked in a simple wavefront controlled treatment plan. Elpins' observation was confirmed in a prospective study of LASIK patients, which found greater reductions in corneal astigmatism and better visual results under twilight conditions using wavefront technology combined with vector analysis (Elpins method) than using wavefront technology alone; equivalent higher-order deviations were also found.

No good data were found to compare the percentage of LASIK procedures that use wavefront control versus the percentage that are not used, and the percentage of refractive surgeons preferring one method or another. Wavefront technology continues to be seen as a "progression" in LASIK with perceived benefits; however, it is clear that not all LASIK procedures are performed with wavefront control.

Surgeons still claim that patients are generally more satisfied with this technique than with previous techniques, especially for the less common halos, a visual artifact caused by a bispherical deviation that has occurred in the eye with earlier techniques. Based on their experience, the US Air Force described the wavefront controlled LASIK procedure as providing "superior vision results."

LASIK surgery results

The planning and analysis of corneal reshaping techniques such as LASIK has been standardized by the American National Standards Institute, an approach based on the Elpins astigmatism analysis method. The FDA website states the following in relation to LASIK:

Before undergoing a refractive procedure, you should carefully weigh the risks and benefits against your own value system and try to avoid being influenced by friends who have undergone the procedure or encouraging you to do so.

Patient satisfaction

LASIK surveys reveal a 92-98% patient satisfaction rate. In March 2008, the American Society for Cataract and Refractive Surgery published a meta-analysis of patient satisfaction based on 3,000 reviewed articles from international clinical journals. Data from the previous 10 years revealed a 95.4% level of patient satisfaction among LASIK patients.

Disagreements over safety and effectiveness

The reported safety and efficacy data are open to interpretation. In 2003, the Medical Workers' Union (MDU), the largest medical insurance company in the United Kingdom, reported a 166% increase in claims for laser eye surgery; however, the MDU argued that some of these claims are primarily the result of unrealistic expectations of LASIK patients, rather than defective surgery. In a 2003 study published in the medical journal “ Ophthalmology”, It was found that almost 18% of treated patients and 12% of treated eyes required re-treatment. The authors concluded that greater initial correction, astigmatism, and older age are risk factors for LASIK retreatment. In 2004, the National Institute for Health and Quality of Care of the UK National Health Service (NICE) reviewed a systematic review of four randomized controlled studies prior to issuing recommendations for the use of LASIK in the UK National Health Service (NHS). Regarding the effectiveness of the procedure, NICE reported:

Current data on the LASIK procedure for the treatment of refractive errors indicate that it is an effective method for selected patients with mild to moderate myopia,

Evidence suggests that it is less effective in severe myopia and hyperopia.

With regard to the safety of the procedure, NICE advised that:

There are concerns about the safety of the procedure in the long term, and the available evidence is not sufficient to support its use in the NHS without specific conditions for consent, audit or research.

Several refractive surgeons in the United Kingdom and the United States, including at least one study author cited in the report, suggested that NICE relied on highly outdated and poorly researched information. Revised Recommendations (IPG164) NICE issued in March 2006 stating that:

Available evidence suggests that photorefractive (laser) surgery to correct refractive errors is safe and effective for use in appropriately selected patients.

On October 10, 2006, the WebMD website reported that statistical analysis found that the risk of infection for contact lens wearers is higher than the risk of infection from LASIK. People who wear contact lenses daily have a 1 in 100 chance of developing a serious contact lens-related eye infection after 30 years of use, and a 1 in 2000 chance of significant vision loss as a result of infection. Researchers have calculated that the risk of significant vision loss from LASIK surgery is approximately 1 in 10,000 cases.

On February 25, 2010, Morris Walkler, former FDA Approval for Laser Vision Correction Devices (LASIK), raised concerns about the risk of serious side effects from LASIK and the original FDA approval process. His concerns about LASIK safety were discussed in an interview on the program “ Good morning america". On January 6, 2011, Walkler requested that

“The Food and Drug Administration Commissioner has withdrawn FDA approval (PMA) for all LASIK devices and issued a Public Health Alert with the Voluntary Recall of LASIK devices to stop an epidemic of permanent eye damage caused by lasers and microkeratomes used for LASIK laser vision correction "

Walkler argued:

The FDA was not fully aware of LASIK injuries prior to and during reviews of FDA filings in support of the safety and efficacy of LASIK devices under 21 CFR 812 and 21 CFR 814. In addition, LASIK manufacturers and their employees refused to release safety information and effectiveness from their FDA reports on research exempt devices (IDEs). In addition, they hid the LASIK injuries from the FDA in the context of the amicable agreement of countless lawsuits. IDE-sponsored trials selected the best data, withheld and withheld from the FDA information that clearly indicated that LASIK had an excessive adverse event rate (greater than 1%). These actions were an industry-wide effort, orchestrated in whole or in part by manufacturers and their employees, to circumvent FDA law and regulation. I will provide confidential information on these matters separately to the FDA's Criminal Investigations Department.

Patient dissatisfaction

Some patients with poor outcomes from LASIK surgical procedures report significantly reduced quality of life due to vision problems or physical pain associated with the operation. Patients affected by complications from LASIK have created websites and discussion forums where future and past patients can discuss surgery. In 1999, Ron Link, an RK patient in New York, founded Surgical Eyes as a resource for patients with complications from LASIK and other refractive surgery. Since then, Surgical Eyes has evolved into the Vision Post Surgery Rehabilitation Network (VSRN). No patient protection organization has changed its official stance on refractive surgery, despite claims by Morris Walkler, Ph.D., of criminal behavior during the approval process. Between 1998 and 2006, the US FDA received 140 "negative LASIK reports."

Higher order deviations

The term “higher order abnormalities” refers to vision problems that require special diagnostic tests that cannot be corrected with ordinary glasses. Among such deviations are “flashes”, “phantom images”, “halos”, etc. Some patients describe these signs after surgery and associate them with the LASIK technique, including flap formation and tissue ablation.

Improvements in LASIK technology have reduced the risk of clinically significant visual impairment after surgery. There is a relationship between pupil size and abnormalities that can result from uneven corneal tissue between the intact portion of the cornea and the portion that has been reshaped. Daytime vision after LASIK is optimal as the pupil size is smaller than the LASIK flap. However, at night, the pupil can dilate so that light passes over the edge of the LASIK flap, which causes deviations. LASIK and PRK can cause spherical deflection if the laser makes insufficient correction as it moves outward from the center of the treatment area, especially when most of the correction has been made.

Others suggest that higher order abnormalities were present prior to surgery. They can be measured in micrometers, where the smallest FDA approved laser beam is approximately 1,000 times the 0.65mm. In situ keratomileusis, performed at an older age, increases the incidence of higher-order corneal wavefront abnormalities. These factors demonstrate the importance of careful patient selection for LASIK treatment.

Other side effects

The Patient Advocacy Group, USAeyes lists the most commonly reported complications of LASIK:

· Dry eyes from surgery;

· Over or under correction;

Deficiency of vitamin D from sensitivity to the sun and therefore avoidance;

· Fluctuations in visual acuity;

· Halos and flares occur around bright light at night. At night, the pupil can dilate and become larger than the flap, leading to changes in the flap or stromal edge, causing visual distortions that do not occur during the day when the pupil is smaller. An eye exam for large pupils is done before surgery when the risk of this symptom is being assessed.

• Phantom images or
• Double vision;
• Light sensitivity;
• Large pupils;
• Eye lid irritation;
• Stretch marks (wrinkles on the flap);
• Decentralized ablation;
• Foreign bodies or growth under the flap;
• Thin or looped flap;
• Induced astigmatism;
• Stretching of the cornea;
• Flies in the eyes;
• Erosion of the epithelium;
• Department of the posterior vitreous body;
• A spotted hole occurs with a frequency of 0.3%;
• Light contamination (glare) is another complication commonly reported by LASIK patients.

Dry eyes

Most often, patients after refractive surgery complain of dry eyes. It is reported by some patients in the period immediately after the operation and in the late postoperative period. In 2001, Finland reported a 48% incidence within 6 months of LASIK surgery. In 2006, the US reported a 36% incidence within 6 months. Treatments include artificial tears, precharged tears, and puncture occlusion. Punctual occlusion involves inserting a collagen plug into the lacrimal canal (natural drainage of the eye).

Some patients complain of dry eye symptoms, despite this treatment, dry eyes can be permanent. The incidence of persistent dry eyes is estimated at 28% for Asian eyes and 5% for European eyes. Approximately 90% of the sensory nerves in the cornea are separated in LASIK. Sensory nerve fibers in the cornea are important for stimulating tear formation. One year after LASIK, the bundles of nerve fibers located under the basement membrane are less than half their normal density. Five years after LASIK, the nerves located under the basement membrane for the first time return to a density that does not differ significantly from the density before LASIK. Some patients also experience responsive lacrimation, in part to compensate for the chronically decreased basal tear production.

Complications after laser vision correction

Complications of the LASIK procedure are classified as preoperative, intraoperative, early postoperative, or late postoperative:

Intraoperative complications with a flap

The incidence of flap complications is estimated to be approximately 0.244%. Complications with a flap (such as a displaced flap or folds in the flap requiring movement, diffuse lamellar keratitis, and epithelial ingrowth) are common for lamellar corneal surgeries, but rarely result in permanent loss of visual acuity. The incidence of these microkeratome-related complications decreases as the experience of the treating clinicians increases.

Slipped flap

A "slip-off flap" is a corneal flap that has become detached from the rest of the cornea. Chances of this are greatest after surgery, so patients are usually advised to go home and sleep to allow the flap to stick together and heal. Patients are usually given sleeping goggles or protective pads that are worn for several nights to prevent the flap from dislodging during sleep. A short operation can reduce the chances of this complication, as there is less time for the flap to dry.

Particles inside the flap

Particles of the inner surface of the flap "have an uncertain clinical significance. Particles of different sizes and reflections are clinically visible in approximately 38.7% of eyes examined in the study of transparent media of the eye and in 100% of eyes examined in confocal microscopy.

Early postoperative complications

Diffuse lamellar keratitis (DLK)

DLK is an inflammatory process with the accumulation of white blood cells in the inner surface between the ASIK flap and the underlying corneal stroma. The American organization "USAeyes" reports the occurrence in 2.3% of cases after LASIK surgery. It is most often treated with steroid eye drops. Sometimes the eye surgeon needs to lift the flap and manually remove the accumulated cells.

Infection

The incidence of infectious reactions to treatment is estimated at 0.4%.

Keratoconus

Keratoconus is a genetic condition that causes thinning of the cornea after surgery. Although preoperative screening is done for this condition, it is possible that in rare cases (about 1 in 5000) it appears later with age (after 40 years). If it does, the patient may require rigid gas permeable contact lenses, intrastromal corneal rings and segments (Intacs), corneal collagen crosslinking with riboflavin, or corneal transplantation.

Subconjunctival hemorrhage

There are reports of cases of subconjunctival hemorrhage, which is estimated at 10.5%.

Late postoperative complications

The abundant data on the chances of long-term complications are not yet proven and are subject to change due to advances in experience, instruments and techniques.

Ingrowth of the epithelium

The incidence of epithelial ingrowth is estimated at 0.1%.

Late traumatic flap displacement

There are reports of cases of late traumatic flap displacement seven years after laser vision correction LASIK.

Other

Micro-fold formation

Micro-fold formation is defined as “the most inevitable complication of LASIK procedure, the clinical significance of which seems insignificant”.

Glaucoma diagnostics

After LASIK surgery, it can be more difficult to measure intraocular pressure (used to diagnose and treat glaucoma). The changes also affect the calculations used to select the correct artificial lens for cataract surgery. This is known as a "refractive surprise". Preoperative, operative and postoperative measurements can assist.

Rare cases

• Retinal detachment: The incidence of retinal detachment is estimated at 0.36%;
• New vessel formation in the choroid: the incidence of new vessel formation in the choroid is estimated at 0.33%;
• Uveitis: The incidence of uveitis is estimated at 0.18%.

Climbers

Although the cornea usually becomes thinner after LASIK surgery due to the removal of part of the stroma, refractive surgeons try to maintain maximum thickness to avoid structural weakening of the cornea. Decreased atmospheric pressure at higher altitudes did not appear to pose an undue hazard to LASIK patients. However, some climbers experience myopic changes at very high altitudes.

Effect on leukocytes and corneal keratocytes

There are reports of a decrease in the number of keratocytes (fibroblasts) of the cornea after laser vision correction LASIK.

The onset of senile hyperopia

People with myopia (nearsighted) who are approaching a certain age (after 40 - closer to 50) when they need reading glasses or bifocals may find that they still need reading glasses, despite that they had undergone refractive LASIK surgery. In general, nearsighted people need reading glasses or bifocals later in life than emmetropic people (who see without glasses), but this benefit can be lost if they undergo LASIK. This is not a complication, but the expected result of the physical laws of optics.

While there is currently no method to completely eliminate the need for reading glasses in this group, it can be minimized by performing a variant of the LASIK procedure called "light monovision". In this procedure, performed in the same way as LASIK vision correction, the dominant eye is adjusted for distance vision and the non-dominant eye for the patient's reading glasses prescription. This allows the patient to achieve an effect similar to wearing bifocals. Most patients tolerate this procedure very well and do not notice any changes between near and far vision, although a small percentage of patients find it difficult to adapt to the effect of monovision. This can be verified for a few days before surgery by wearing contact lenses that mimic the effect of monovision. A variant of the PresbyLASIK laser ablation model has recently been developed to reduce or eliminate dependence on reading glasses while maintaining distance vision.

Age considerations

New advances in vision correction surgery provide patients with greater choice. People in their 40s and 50s who are considering LASIK laser vision correction to improve vision may also consider evaluating for implantable lenses, especially if there are signs of an early stage cataract.

This is both a symptom of dangerous conditions and just a cosmetic defect. But is it a drawback? Rather a highlight, although if the size of the pupils is very different, it looks quite intimidating at first glance.

Most people know that the pupils dilate and contract under the influence of light, capturing just as much as needed for more or less normal vision. So, when you see someone's pupils of different sizes, especially if the difference is insignificant, you should not raise the alarm - you need to ask the person to turn to face the light and compare the size of the pupils again, perhaps it was precisely the fact that a different amount fell on different eyes Sveta.

If pupils of different sizes differ significantly in the light and in the twilight, that is, the difference between them greatly increases or decreases, this is already a reason to visit doctors in the near future, even if vision does not suffer.

The use of special ophthalmic drops can also dilate one pupil, making the person look intimidating. In this case, vision will be blurry, even if myopia or farsightedness is not diagnosed. However, the action of the drops passes rather quickly, so this condition cannot be called pathological.

Sometimes, as doctors say, such a reaction can be observed on some vaccine vaccines, which, in general, is also quite harmless. On the other hand, a symptom such as pupils of different sizes, the reasons for which are not clear, may indicate serious

Diseases of the eyes, brain and the rest of the nervous system.

The first thing to do in this case is to ask the person if they have recently had a head injury. If the answer is yes, it is better to play it safe and go to the hospital, since serious brain damage can lead to a very, very sad outcome, while timely medical assistance can save another life.

In children, pupils of different sizes can be observed due to birth trauma. So a visit to a pediatric neurologist on this issue is mandatory.

If there were no head injuries, you should immediately visit an ophthalmologist, as well as a neurologist. In the event that specialists do not find any diseases and pathologies in their area of \u200b\u200bcompetence, you can continue to surprise people with such an unusual appearance. For example, David Bowie has lived with such a twist since adolescence when he suffered an eye injury. However, his eyesight remained the same, and his strange appearance, perhaps, even added to his popularity.

Pupils may also remain different for some time after various operations. Usually doctors talk about 1-3 months, but it happens that the full function of the muscle responsible for dilating and narrowing the pupil is not restored.

It's simple: you don't need to panic when you see different pupils, especially if visiting doctors has already given you confidence that there are no diseases or injuries. Unfortunately, the cosmetic defect is almost impossible to remove. And is it necessary, especially if there are no inconveniences?

Pupils of different sizes are quite rare, but this also happens. In order to understand why this happens, you need to familiarize yourself with the structure of the pupil. So, the pupil is a kind of opening that is formed by the free edges of the iris. The location is not in the center, but slightly offset inward and downward. Black aperture means reticulated shell. The pupil performs the main function - it regulates the amount of light rays transmitted to the retina. If a person looks at a bright light, then the pupil decreases slightly in diameter, due to which the light rays are cut off.

This results in image clarity. In the dark, the hole, on the contrary, becomes wider. Pupil constriction or dilation is achieved by a muscle that is innervated by sympathetic nerves. But the sphincter muscle is controlled by the parasympathetic nerves. Thus, when a person experiences a feeling of fear, severe fright, pain syndrome, the sympathetic nervous system is activated, due to which the pupil expands. In addition, the pupil can expand at the moment of turning the eyeball towards the nose and when looking from an object that is close to a distant image. This is considered the norm. If pupils of different sizes are noted not under such circumstances, then we should talk about a pathology that is called anisocoria.

Different pupil sizes are divided into two main types - physiological and congenital. Physiological anisocoria is assigned when there is a difference between the size of the pupils, but no diseases have been identified. This condition can be attributed to the individual characteristics of the human body. In addition, the disease is subdivided into subspecies, depending on the age of the person, since the causes of occurrence are different.

Newborns, children

Pupils of different sizes in a child who has just been born indicate a congenital form of pathology. It could also be a sign of another disease or disorder. For example, if anisocoria occurs suddenly, then the cause may be brain injury, the presence of a neoplasm, aneurysms of the circulatory system in the cranial cavity, or encephalitis. If a child was born with a pathology, then the cause may be the underdevelopment of the autonomic NS or congenital diseases of the iris. As a rule, it is accompanied by drooping of the eyelid or strabismus. For the older child age category, a different etiology is characteristic. So, different pupils in size in a child are the reasons:

1. Injury to any part of the brain or visual apparatus.
2. Postponed eye surgery. Most often in this case, the sphinx or the iris is damaged.
3. Encephalitis, meningitis.
4. Inflammatory processes in the iris and vascular aneurysm.
5. Neoplasms in the brain.
6. Intoxication with poisons and overdose when taking medications.
7. Adie's syndrome.

Adult population

The reasons for the different sizes of pupils in an adult:

1. Diseases of an ophthalmic nature. These include uveitis, iridocyclitis, iritis. Also, the consequences after the surgery and the presence of an implant in the cavity of the visual apparatus.
2. Neurological reasons with a bright manifestation in the dark. Feature: a pathological deviation refers to the pupil, which is more narrowed (smaller in size). This happens with the syndrome of Adie, Horner and damage to the fibers of the motor nerves of the eye that are not ischemic. Horner's syndrome deserves special attention, since it develops against the background of a huge number of pathologies of the brain, cervical spine and oncological diseases. This type is characterized by a delay in the expansion of the pupil with a sharp change in light. For example, when a person goes from a lighted room to a completely dark one.
3. Neurological diseases in which anisocoria is more pronounced in bright light. A pathological disorder is noted in the dilated pupil. This form arises due to paralysis of the motor nerves of the visual apparatus, which develops against the background of strokes, aneurysms, neoplasms and inflammatory processes in the brain.
4. Another reason for pupils of different sizes can be long-term use of certain groups of medicines. For example, anticholinergics or sympathomimetics. Quite often, anisocoria occurs with herpes zoster, which is localized in the ciliary ganglia.

Main symptoms

1. Deterioration of visual acuity and blurred vision.
2. Doubling of objects and loss of vision.
3. Fear of bright lights and headaches.
4. Impaired consciousness and pain in the visual apparatus.
5. Nausea and vomiting.
6. Increased body temperature.

Diagnostics and treatment

In order to diagnose a disease in which pupils of different sizes are noted, it is necessary to consult an ophthalmologist. After a thorough examination, the doctor will prescribe the appropriate treatment.

Diagnostics

Diagnosis includes a visual examination of the visual apparatus and instrumental research methods. This can be ophthalmoscopy, magnetic resonance imaging using a contrast agent, EEG. In addition, the ophthalmologist measures intraocular pressure, examines the cerebrospinal fluid. Additionally, X-ray of the lungs and Doppler ultrasonography of the circulatory system of the brain can be performed.

Treatment methods

The method of treatment is prescribed based on the etiology and causes of pupils of different sizes. So, if a congenital or physiological form is diagnosed, then treatment may not be prescribed at all, since this is not considered a pathological deviation. For inflammatory processes, antibacterial therapy is used, for neoplasms - surgical intervention. If encephalitis, meningitis and the like are observed, then only complex treatment is carried out. In the event that the disease does not require treatment, but the patient wants to correct the defect, an operation may be prescribed. In many cases, eye drop therapy can be used. Often. Anti-inflammatory and corticosteroid medications may be prescribed depending on why the pupils of different sizes have arisen.

ATTENTION! It is strictly forbidden to engage in self-treatment and use eye drops. Remember, drug therapy can only be prescribed by an ophthalmologist after a thorough examination.

Complications

If you do not pay attention to pupils of different sizes in a timely manner, especially in the form that requires surgical intervention, serious disorders can follow, which lead to the development of diseases of the eyes, circulatory system and brain. In some cases, the outcome can be fatal.

For doctors

In the tropical jungle, a narrow specialization becomes the key to survival. There are flowers that receive food only in the form of insects caught and killed by them. And there are insects that eat only their fellows caught by these flowers. So now in medicine, universal doctors are being supplanted by super-narrow specialists who have become hostages of the development of medical science and technology. Twenty years ago, an ophthalmologist was considered a narrow specialist, then ophthalmic surgeons and ophthalmotherapists appeared, then neuro-ophthalmologists, ophthalmoendocrinologists and refractive surgeons. More and more often there are doctors of one operation, and in Fedorovskaya "Romashka" there were even doctors of one stage of surgical intervention.

Abroad, they are trying to stop the endless narrowing of doctors' specialization, provoked by the collapse of new technical innovations, by creating an extensive layer of paramedics, in our opinion, paramedics, who perform part of the medical functions, mainly related to diagnostic manipulations on semi-automatic equipment. However, it is impossible to defeat the narrowing of specialization initiated by the development of civilization.

Narrow specialization leads to the fact that in other, related, areas of specialist knowledge become superficial. This book will enable oculists in other areas of ophthalmology and other medical specialties to understand the principles of laser correction. After all, doctors - "neophthalmologists" have relatives, acquaintances and patients who ask for advice on laser correction. It's always nice when someone's opinion is balanced and well-reasoned.

The third part of the book, I hope, will be of interest not only to curious readers, future and former patients and doctors of various specialties, but also to refractive surgeons themselves. For beginners, anyway. Not because some unique and cutting edge data on refractive surgery will be presented here. On the contrary, I would like to highlight here the practical side of laser correction, which is only mentioned in passing in scientific monographs, articles and abstracts. Some of the minor techniques used in diagnostic and surgical procedures. Features of the interpretation of aberrometry data. Refractive surgery innovations. A novice surgeon should receive all this knowledge not from popular science books, but through practical training. However, in Russia there is still no single training center teaching methods of excimer laser vision correction.

So, here is some information about excimer laser correction of ametropia and other aberrations.

A look from the other side, or Again about the survey

Again?

Here I want to give as much detail as possible, but within reasonable limits, to answer the question: "Why is this necessary for laser correction?" In general, the information is at the "advanced user" level.

Ametropia

Let's start with the classification of ametropia.

1. Strong (myopia) and weak (hyperopia) refraction.

2. Conditionally spherical (without astigmatism) and aspherical (with astigmatism).

3. Weak (less than 3 diopters), medium (from 3.25 to 6 diopters) and high (more than 6 diopters) ametropia.

4. Isometropic (the difference between the eyes is 1 diopters or less) and anisometopic (the difference between the eyes is more than 1 diopters).

5. Congenital, early acquired (acquired at preschool age), acquired at school age, late acquired.

6. Primary and secondary (induced).

7. Complicated (with changes in the anatomical and functional state of the eye) and uncomplicated.

8. Stationary and progressive.

Poll

The first is how long the patient has worn contact lenses and how long ago they last removed them. Asked this means they have completed 50% of the survey.

Second - when did myopia appear and is it progressing now? If it appears after eighteen, then, in the worst case, keratoconus can be suspected, and at best, myopia may progress after the correction.

The third is the epidemiological anamnesis. Together with blood tests for infections you know what it is for, but for refractive ophthalmology this is not so important. You just need to force the patient to donate blood for analysis.

It is only needed for carrying out visometry ("vision measurement" - visual acuity test) with correction. That being said, ARM provides a ton of preliminary information. A sphere greater than +5 diopters is a reason to think about refusing laser correction and, possibly, about aspiration of a transparent lens (respectively, threefold ultrasound biometry for the subsequent calculation of the optical power of the artificial lens).

A sphere larger than –6 diopters forces us to ask in advance whether the patient underwent prophylactic laser coagulation of the retina. Today, such a strengthening of the retina is a controversial procedure. However, with ophthalmoscopy, you will still need to closely look for retinal breaks.

Keratometry data on one of the axes greater than 46 diopters and complex myopic astigmatism with oblique axes (about 45 ° or 135 °) may be signs of keratoconus. There are many other indirect signs of keratoconus, which should force pachymetry and keratotopography to be done more carefully. These include:

visual acuity with correction is less than 0.8;

significant improvement in visual acuity without spectacle correction, but through the diaphragm (a small hole with a diameter of 1-3 mm);

surprisingly good vision without glasses at high diopters;

noticeable fluctuations in the optical power of astigmatism and its axes during repeated measurements (including cycloplegia).

It is worth mentioning that if the keratometry data is less than 40 diopters, then, perhaps, the patient has already undergone keratorefractive surgery for myopia.

And in general it is worth keeping in mind the ratio of keratometry data and the size of the anteroposterior segment (PZO) of the eyeball. Keratometry is inversely proportional to PZO. The more keratometry, the less the PZO should be and, conversely, the less keratometry, the more PZO should be (up to the need for prophylactic laser coagulation for low myopia).

For example, normally:

with keratometry data of? 43.0 diopters, the PZO should be? 24.0 mm;

when keratometry data is? 46.0 diopters, the PZO should be? 23.0 mm;

with keratometry data of? 40.0 diopters, PZO should be? 25.0 mm.

keratometry data - 43.0 and PZO - 26.0 mm, then this is weak or moderate myopia (it is with this ratio that it may be necessary to carry out preventive laser coagulation of the retina, despite the low degree of myopia);

keratometry data - 46.0 and PZO - 26.0 mm, then this is high myopia;

keratometry data - 40.0 and PZO - 24.0 mm, then this is hyperopia.

Any violation of the ratio of keratometry and PZO, in fact, leads to the appearance of myopia or hyperopia. And laser correction only brings the ratio of keratometry and PZO back to normal, changing the curvature of the cornea. As for the absolute values \u200b\u200bof keratometry and PZO, which I have just given in the example, these are purely approximate figures that only illustrate the principle of regularity. These ratios do not take into account the individual parameters of the lens, which for some may be 3 mm thick, and for some - 5 mm (which can be found out when performing ultrasound biometrics simultaneously with the PZO measurement).

By the way, many survey parameters become more informative and reliable when constantly compared with each other. And such juggling with numbers is a must when examining every patient.

Non-contact tonometry of intraocular pressure (pneumotonometry)

Increased ophthalmotonus in excitable (nervous) young patients is quite common, and glaucoma should not be suspected in everyone. However, it is also possible to miss "young" glaucoma in such cases. It makes sense at 2-3 "extra" mm Hg. Art. still carry out medical expansion of the pupil (mydriasis), which should provoke an increase in pressure in glaucoma. And if during mydriasis, instead of lifting, the pressure remains the same or even decreases, it means that a kind of stress test did not confirm glaucoma. If the intraocular pressure from the drops still increases, we immediately prescribe diuretics (therefore, before mydriasis, it is better to ask if the patient has prostate adenoma and if so, it is better not to drip). If there is a suspicion of glaucoma, then you should not carry out such a provocation with mydriatics. It is better to approach the development of the examination algorithm more conservatively: Maklakov tonometry, electrotonography, perimetry. Until you diagnose "glaucoma" or refute it, I do not recommend doing laser correction. After correction, the diagnosis will be more difficult.

With "ophthalmic hypertension" or symptomatic hypertension (a tendency to increased intraocular pressure) there is a risk of refractive regression of the LASIK result. The pressure pressing from the inside of the eye on the cornea that suddenly becomes thinner after LASIK, in the first months before the healing stabilizes, can slightly "stick out" it, 1-2 diopters can return. In this case, additional correction will help as usual, but the patient must be warned about this in advance. And about the increased attention to your intraocular pressure after forty years too. And to prevent such a regression, it makes sense to instill drugs that reduce intraocular pressure within a month after the operation. Moreover, it is better to prescribe drugs that do not improve outflow (arutimol), but reduce the volume of tear production (betoptic).

And further. During the preoperative examination, the physician should pay attention to the relationship between tonometry data and pachymetry data (corneal thickness). Juggling numbers again.

Visual acuity

It is necessary to focus the patient's attention on which very bottom line he reads with the maximum spectacle correction. That is how much he will see after laser correction, but without glasses.

An excursion into the characteristics of the resolution of the eye

The evolution of the preoperative relationship between the refractive surgeon and the patient is leading to an increasing awareness of the latter about the possible complications and features of the eye condition after LASIK. Of course, the main criterion for evaluating the effectiveness of refractive surgery is visual acuity. However, visual acuity is only one of the constituent parts of a broader concept - "the resolution of the eye". It is the resolution that most fully characterizes the qualitative parameters of the act of vision. Therefore, when assessing the effectiveness of laser correction, it is necessary to keep in mind three main components of the eye resolution:

visual acuity;

contrast sensitivity;

resistance to glare.

Visual acuity

The following refractive factors affect visual acuity:

the presence of diffractive, chromatic and monochromatic aberrations;

scattering of some part of the light passing through optical media (this scattering increases with age);

absorption (absorption) of a part of light energy by optical media, which in reality are only conditionally transparent (the shorter the wavelength, the smaller part of it reaches the retina);

fuzzy accommodative focusing of the image on the retina due to the absence of sharply outlined "targets" in the field of view.

But the basis for the clarity of image perception is still not only the refractive mechanism, but also the functioning of the retina, the visual pathway and the cerebral cortex. The smaller the innate size of rods and cones, the higher the visual acuity in humans. Visual acuity also depends on the formation of visual sensation in the brain. There are three stages in the formation of visual sensation.

The ability to notice the presence of an object. The ability to notice a stimulus of the minimum size that disrupts the continuity of the visible homogeneous space is not constant for all types of visual objects. For example, black hair 0.12 mm thick can be seen against a white background from a distance of about 12 m, but a point of the same diameter is visible only from a distance of 60 cm. This ability is used in contrast sensitivity testing, which will be discussed below.

The ability to see the structure of an object in detail.

The ability to recognize, identify a visual image in accordance with previously known ideas about objects in the external world. Even if a person is not able to clearly discern the structure of an object in detail (previous ability), the brain is able to guess which object is being discussed based on its own visual experience. The so-called effect of ultra-high visual acuity, which is closely related not only to the volume of previously obtained visual information, but also to the level of human mental development. Of course, mistakes are possible here. When checking visual acuity according to the Golovin-Sivtsev table, a person using his ability to identify can confuse the letters "k" and "b", "s" and "w", "i" and "n".

The combination of some refractive disorders with the formation of a visual image sometimes leads to paradoxical phenomena. One such case is the observation of an object that is beyond the resolution of the retina. That is, the image of a black hair on a white background at a distance of 13 meters from the eye is projected onto the retina as an object smaller than the diameter of the cone. Accordingly, such a small object should not be visible. However, the scattering of a small part of the light energy in the optical media of the eye leads to blurring of the image of an extended visual stimulus (hair), to its increase. And such a "blurry" object becomes available for visualization due to the refractive imperfection of the optical media of the eye and in spite of the resolution of the sizes of the retinal photoreceptors.

Another paradoxical phenomenon is the improvement in visual acuity after the formation of a corneal flap, but without laser ablation. The appearance of higher-order induced monochromatic aberrations leads to blurring of the clinical focus of the eye. From several images, the brain, using the ability to identify a visual image, selects the clearest and most recognizable.

Therefore, it is impossible to make an objective and correct comparison of the visual acuity of two people. All these 1.0 and 0.1 depend on too many reasons to be the absolute truth in assessing the effectiveness of laser correction. It is no coincidence that the qualitative characteristics of postoperative vision have been actively studied in the last decade.

Contrast sensitivity

Contrast sensitivity - the ability to capture minimal differences in the illumination of two adjacent areas and differentiate them in terms of brightness.

Visual acuity reflects the minimum size of characters distinguishable by the eye that have maximum contrast with the background. Lack of measuring visual acuity in its one-dimensionality. Contrast sensitivity allows you to evaluate 2D and 3D objects.

The contrast sensitivity of the visual analyzer allows:

Inform about small details of the object.

Perceive a holistic image of an object.

Analyze the contours of the object qualitatively.

Resistant to glare

With pronounced background brightness and low object brightness, it is difficult to see objects that are clearly distinguishable in a different brightness ratio. Such a phenomenon can be observed when peering into a distant tree against the backdrop of a cover sparkling under the sun. It is also impossible to see a partial solar eclipse without a special light filter. In everyday life, drivers often encounter dazzle - blinding by the headlights of an oncoming car: the details of the road are no longer visible.

Blindness, or glare effect, is a sensation caused by a light that appears in the field of vision, stronger than the one to which the eye is adapted, and expressed in visual discomfort, decreased visibility or temporary loss of performance.

Cataract, epithelial edema and corneal stromal opacity lead to a decrease in resistance to blinding light, as a result of which, in the presence of a blinding light source, contrast sensitivity decreases, that is, visual acuity decreases.

After laser correction, especially with a thin cornea (and, accordingly, narrowing of the laser ablation zone), despite the achieved maximum possible visual acuity, patients sometimes complain of visual discomfort in low light conditions. Such complaints are associated with a slight decrease in contrast sensitivity and resistance to glare. Before carrying out laser correction, a refractive surgeon must warn the patient about the possibility of such violations of the resolution of the eye. Sometimes the doctor experiences great difficulties in trying to explain the essence of the violations, however, the patient must decide on such costs of the postoperative quality of vision before the laser correction.

Biomicroscopy

It is imperative to inspect the anterior part of the eyeball with both narrow and wide pupils. With a narrow pupil, one can notice a sign of a slight subluxation of the lens - iris tremor (iridodonesis), with a wide pupil - single point opacities of a congenital nature along the periphery of the lens. Both are best noted on the examination sheet and notify the patient. In order not to have to make excuses after LASIK in front of a patient who can present subluxation and “initial” cataract as a complication of laser correction.

Biomicroscopy is a treasure trove of information and a supplier of contraindications. It is pointless to list all of them. Just a few statements on the most popular sensitive issues.

Severe sclerosis of the lens (phakosclerosis) is not a contraindication to laser correction. The patient should be aware of the possibility of developing cataracts. The operation to remove the lens after laser correction can be done no earlier than 6 months later, and the surgeon should be warned about the correction method used.

Thinning or discontinuity of the pigment border of the iris, exfoliation, small anterior chamber are signs of glaucoma.

If the conjunctiva is prone to allergic reactions and, in general, if there is a tendency to chronic manifestations of allergies, antihistamine tablets (antiallergic) should be prescribed for the first postoperative week. This can reduce the risk of diffuse lamellar keratitis.

When the pterygoid hymen (pterygium) protrudes more than 1 mm into the "territory" of the cornea, it is necessary to first remove the pterygium, and then, not earlier than 1–2 months, perform LASIK.

With a very wide senile arch (arcus sinilis) or other corneal dystrophies, it is better to observe the progression throughout the year. The senile arch, of course, is not a contraindication to laser correction, but another nosology can mimic it. Not every type of corneal dystrophy can be diagnosed without dynamic observation and additional examinations (confocal microscopy, consultation of a geneticist, etc.).

Anterior and posterior synechiae (“accretion” of a part of the iris to the cornea or lens due to inflammation or trauma), if possible, is best removed with an appropriate laser a few days before the examination under cycloplegia. Distortion of the shape of the pupil due to the presence of synechia during aberrometry can adversely affect the reliability of the examination and subsequently on the results of LASIK.

Perimetry

Examination of the visual fields, in this case screening (fast and massive), allows diagnosing diseases of the retina and optic nerve, as well as neurological pathology (in particular, damage to the chiasm in pituitary adenoma, etc.). Not all of them are contraindications to LASIK. Loss of half of the visual field (homonymous or heteronymous hemianopsia), if the disease does not progress, and the patient sees much better with spectacle correction than without it, is not a contraindication to laser correction. Quite often the word "laser" has a magical effect on people, and they hope to cure all eye diseases with its help. The patient should not harbor false hopes and should be aware of the risk of neurological disease progression in the future.

Another thing is with the steady progression of the disease, in particular with tapetoretinal abiotrophy (a hereditary disease, due to which retinal cells gradually but irreversibly die), in principle, laser correction is absolutely contraindicated. At the insistence of the patient, there may be exceptions. But the patient should be aware that sooner or later he will become visually impaired, and the task of doctors is to prepare him for this, both emotionally and professionally, and not offer him laser correction.

Ophthalmoscopy

It is better to reflect the state of the retina in detail in the advisory opinion, so that later there are no misconceptions such as "because of LASIK myopic cone appeared". Prejudice and fear grow in direct proportion to people's belief in the endless possibilities of lasers.

Other aspects of diagnostics are standard and no comments.

In ophthalmology, it is widely believed that accommodation spasm is possible only in childhood and adolescence. And if a person is over forty, then a spasm simply cannot be. Error. Conducting cycloplegia in patients with symptoms of presbyopia in a very significant percentage of cases leads to a change in refraction. Therefore, regardless of the patient's age, it is necessary to calculate the parameters of laser ablation ONLY according to the data obtained under cycloplegia. I know there are different approaches to this issue, but I will not mention them here.

Visometry with a wide pupil is not a diagnosis, nor is it obtaining true parameters. Just order and habit. The diaphragm, with which visual acuity is checked for a wide pupil, neutralizes the effect on vision of some aberrations (mainly astigmatism), and visual acuity without correction improves (a phenomenon used in "perforated" laser vision glasses). This "vision with a diaphragm" has nothing to do with the patient's real life.

Keratotopography or aberrometry

More on this in the next chapter.

Ultrasound diagnostics

Ultrasound biometrics, A- and B-scanning.

Pachymetry

Ultrasonic or optical. Cardinal examination. And the final one. After that, only the conversation with the patient remains.

The most significant are the pachymetry data in the center. And not even in the center, but at the point where the thickness of the cornea is minimal. If this point is not near the center, but closer to the lower periphery of the cornea, then this is an indirect sign of keratoconus. Or damage to the corneal epithelium during the examination (ultrasound pachymetry, A-scan). After all, the epithelium, after all, is about 50 microns thick, and any of its depression or micro-erosion can significantly distort the pachymetry data.

In myopia correction, the deepest point of the laser ablation profile is in the middle. And when correcting hyperopia, some use pachymetry in the area of \u200b\u200bthe future corneal groove, 2.5–3 mm from the center of the cornea. The cornea is much thicker towards the periphery than in the center. It is possible, like, and the thickness of the ablation can be calculated large. Should not be doing that. With laser correction of hyperopia, we create a corneal profile of pseudo-keratoconus with a local "bulging" and excessively reduce the thickness of the cornea along the periphery. The risk of turning pseudo-keratoconus into iatrogenic is too great.

And now about the ratio of corneal thickness and intraocular pressure. Juggling numbers again.

If the intraocular pressure (IOP) is 23 mm Hg. Art. (at a rate of up to 21 mm Hg with pneumotonometry) and a corneal thickness of 600 microns is normal. Because several mm Hg. Art. the increased "stiffness" (biomechanical properties) of the thick cornea adds to the true pressure. That is, the real pressure of a person is not 23, but about 18 mm Hg. Art.

If the IOP is 20 mm Hg. Art. and the corneal thickness of 480 µm is the increased intraocular pressure. Because a thin cornea is too soft and resists the air jolt that it receives during tonometry with less force than the average eye for which everything is designed (cornea thickness in the optical center is on average 550 microns).

True IOP helps to determine the recently appeared ophthalmic apparatus - an analyzer of the biomechanical properties of the cornea.

Diagnostic trivia

Often faced with patients who work in the dark or, even worse, living in the polar night, the doctor begins to pay attention to the size of the pupil in the dark during the examination. If the diameter of the pupil in the dark is significantly larger than the expected area of \u200b\u200blaser ablation, then this can lead to a significant decrease in twilight vision and inability to perform official duties at night. And the patient must be warned about this before the laser correction.

True, modern algorithms for laser ablation have significantly reduced the risk of such problems. With sufficient thickness, it is possible to form a very shallow transition zone, i.e. a very gradual transition between the place where the evaporation of the corneal stroma was carried out and the periphery not affected by laser exposure.

Examining a person of intellectual work or a representative of "office plankton", the doctor purposefully begins to look for signs of dry eye syndrome. An invaluable diagnostic method here is the Schirmer test, designed to determine the volume of tear production. To do this, paper of filter indicator paper is placed in the lower eyelids and asked to sit like this with closed eyes for 5 minutes. If a tear wets 15 mm of paper or more in 5 minutes, the test result is good and there is no cause for concern. 0 mm, 5 mm and 10 mm tear wetting of the filter paper indicates different severity of dry eye symptom.

To predict patient satisfaction with the results of laser correction, the volume of accommodation in patients with a high degree of myopia is also important. The ability to accommodate in such cases is often weakened, which can cause problems with near vision after correction, even at a young age.

It makes no sense to list all such diagnostic trivia here, there is specialized literature for this. But you shouldn't forget about them either.

Talking to a doctor

Leo Tolstoy in the last part of the novel "War and Peace" has the following words: "Doctor ... as doctors, he considered it his duty to have the appearance of a man, every minute of which is precious for suffering humanity ..." And so it is. Nowadays, this kind of doctor is often not a feigned posture, but a natural state associated with an ever-increasing flow of patients and cases. Especially in ophthalmology, especially in refractive surgery.

Performing the LASIK operation at times for more than thirty patients a day, the doctor begins to feel like a conveyor worker. Yes, everything in this conveyor is fine-tuned and does not fail, but there is no time left for a conversation with each patient (in fact, this was one of the motives for writing this book). You have to formulate the main points of what a particular patient should know in a short speech and blur it out with a tongue twister, and then answer the questions that arise. Here are a few of these speeches I bring to your attention.

For a patient with mild to moderate myopia

You have this degree of myopia. You can get laser correction done and eliminate all the myopia you have. There are no difficulties. However, each of us has a different healing process. And if your healing takes place outside the box, then 15 percent of the myopia that is now can return. If this happens and residual myopia bothers you, then no earlier than three months later it will be possible to do the second stage of laser correction (additional correction) and remove this residual myopia. Not from the first, but from the second time you will have the vision that we promised you. What kind of vision do we promise you? The number of lines that you now see in glasses, you will see without glasses. This is not because some "minus" will remain, but because for your brain this number of lines is one hundred percent. You will have such vision, provided that you comply with all the restrictions that are listed in the memo. The main limitation is that you cannot touch, rub your eyes and eyelids (it is more correct to say not to rub, but to “wipe”, but this is clearer). It is better not to touch even the cheek next to the eye. And you must comply with these requirements within one month. Then whatever you want, but you need to be careful for a month.

The only glasses you will need are reading glasses after forty. Not because of correction, just reading glasses are the age norm. Any questions?

For a patient with high myopia (especially with myopia above 8-10 diopters or with corneal thickness less than 520 microns)

You have a high degree of myopia. You can get laser correction done and eliminate all the myopia you have. However, there is a possibility that some of the myopia may return. Each of us has a different healing process. And if your healing takes place outside the box, then 15-20 percent of the myopia that is now, can return in the first month after the correction. There may also be some progression of myopia throughout life. If residual myopia bothers you, then not earlier than in three months it will be possible to do the second stage of laser correction (additional correction) and remove this residual myopia. But if the thickness of the cornea (and your cornea is not very large) does not allow removing all residual myopia, then it may partially remain. You will never have a high degree of myopia, but, say, –1.0 may remain. With such myopia, you do not need to wear glasses all the time, but sometimes you may have to use them (while driving or to watch TV). But after forty years, when everyone is wearing reading glasses, your residual myopia will allow you not to wear such glasses.

If there is no residual myopia, then you will certainly need reading glasses after forty years. Reading glasses are the age norm for everyone.

What else might bother you? Violation of dark adaptation. I think you are still not very comfortable in the twilight and in the dark? And after the correction, these sensations will intensify. In the dark, you may have rainbow circles around light sources, merging of two adjacent lights, blurring, some impairment of peripheral vision. These defects will gradually decrease, but the residual effects can persist throughout life. In ordinary life, such defects do not interfere, you just have to find out about them before correction. However, when you can drive in the dark is hard to say.

I remind you that you must comply with all the restrictions that are listed in the memo. The main limitation is that you cannot touch, rub your eyes and eyelids. Even the cheek next to the eye is better not to touch again. And you must comply with these requirements within one month. Then whatever you want, but you need to be careful for a month. Any questions?

For a patient with high grade astigmatism

You have a high degree of astigmatism. Astigmatism is a congenital irregularity in the cornea (the transparent surface of the eye through which we see). That is, horizontally, you have so many diopters. And vertically - so much. The difference between them is so many diopters. With the help of laser correction with a "guarantee", you can remove 4 diopters. We will eliminate almost all of your astigmatism. But the body over ... years (the patient's age) got used to this unevenness and will try to return what it had. During the healing period, he may partially succeed. If a partial return of astigmatism nevertheless occurs, then not earlier than in three months it will be possible to do the second stage of laser correction (additional correction) and remove this residual astigmatism. However, even after the second stage, a slight residual astigmatism is possible. However, it will not significantly affect visual acuity.

Currently, LASIK is the safest of all methods of surgical correction of astigmatism.

What kind of vision do we promise you? The optimal result is the number of lines you see in the glasses now. After laser correction, you will see them without glasses. Maybe one or two lines less or more.

What else might bother you? Violation of dark adaptation. In the dark, you may have rainbow circles around light sources, merging of two adjacent lights, blurring, some impairment of peripheral vision. These defects will gradually diminish, but residual effects may remain for life. In ordinary life, such defects do not interfere, you just have to find out about them before correction. However, when you will be able to ride in the dark, I cannot say.

The only glasses you will need are reading glasses after forty. Not because of correction, just reading glasses are the age norm. Any questions?

For patients with hyperopia more than +3.0 diopters

You have such a hyperopia. You can get laser correction done. But the main difficulty in laser correction of hyperopia is a partial return of those diopters that you have now. Your visual acuity will certainly improve, but a residual plus is possible. You don't need glasses to wear them all the time. Maybe over time glasses will be needed when driving a car, and certainly, sooner or later, reading glasses will be needed. Especially after forty years, when age-related hyperopia also appears.

If the residual hyperopia is large enough, then with a sufficient thickness of the cornea, no earlier than three months later it will be possible to perform the second stage of laser correction. But even after the second stage, a slight residual hyperopia is possible.

Usually, when correcting myopia, the patient can be promised good vision in a few hours. With the correction of hyperopia, especially quite high, like yours, visual acuity will be restored gradually. Near vision will improve first. Then gradually the point of clear vision will begin to recede.

I remind you that you must comply with all the restrictions that are listed in the memo. The main limitation is that you cannot touch, rub your eyes and eyelids. Even the cheek next to the eye is better not to touch again. And you must comply with these requirements within a month. Then whatever you want, but you need to be careful for a month.

Patient questions when talking with a doctor

Those few stereotypical short speeches above are very exemplary and variable. However, they contain the main summary of the information that the patient should know before the operation. Of course, many people start asking questions after such a short message. The most varied and unexpected. The patient is in a stressful situation, does not behave quite adequately and asks the appropriate questions. Some confusion of consciousness makes it difficult for the patient to perceive, therefore, some points of the message are exaggerated, simplified as much as possible and are partially repeated.

The following are answers to the most frequently asked questions from patients. Other doctors may have different speech and answers to questions, but each doctor has his own motivation, not aimed at the harm of the patient.

When can contact lenses be worn?

Not earlier than in a year. And you will endure them with greater difficulty than before the operation. Contact lenses will have to be removed more often and artificial tears (Oftagel, Systane, etc.) should be instilled in periodic courses. You will not need to wear prescription lenses (there are exceptions with very high myopia and hyperopia against the background of a thin cornea). These are colored contact lenses for changing eye color.

For the first three hours, you will have watery eyes and photophobia. You will have no time for visual stress. Further on portability: tired - rested. True, the more visual loads there are, the greater the likelihood of temporary dryness in the eyes, transient fog, periodic decrease in vision. Although visual stress does not affect the final result, the healing period can be delayed (it will take longer to instill drops). You shouldn't be afraid of this.

When can I go to work?

The next day. But if the work is connected with driving a vehicle or difficult working conditions (dust in the air, harmful fumes, the risk of injury to the eye area, etc.), then you may need to be released from work (sick leave "due to working conditions"). You must assess the situation yourself, taking into account all the restrictions. It's hard to work, you are not sure of your own vision - you go to the clinic at your place of work (or at your place of residence) and “blame” all the blame on the laser correction clinic. The ideal situation is if the clinic in which you operated can give you a sick leave. Several days of sick leave, I think, will be quite enough.

How long do you need to wear sunglasses?

Usually the first three hours while there is photophobia. Glasses are for your convenience only. There is another way to use them. It is advisable to sleep in them for several nights. They will prevent you from rubbing your eyes inadvertently in a dream. In some clinics, an occluder and other devices are used for this purpose.

But no homemade blindfolds! The dressing itself can move the corneal flap!

How much does the second stage cost?

Most often free. Each clinic has its own rules.

When can I play sports?

For one month, mechanical effects on the eyes must be excluded. Accordingly, exclude playing sports (you can hit the ball in the eye, etc.) and martial arts. It is advisable not to experience maximum power loads for a month. For example, when doing powerlifting, bodybuilding and weightlifting, you need to reduce the weight of the apparatus, increase the number of approaches and repetitions, "work on endurance."

I'm going to fly to the sea. Can?

Can. It is recommended to wear sunglasses (with UV protection) outdoors. You cannot dive (the pressure of the water column on the eyes) and it is better not to swim at all. For preventive purposes, it is better to use artificial tear preparations.

After the correction I am leaving quite far.

If I accidentally rub my eye, what should I do?

If, after accidentally rubbing your eye, you feel a sharp deterioration in vision, a feeling of a foreign body in the eye, lacrimation and photophobia, then immediately contact the nearest clinic that makes laser correction, or call the one in which the operation was performed. The clock is ticking!

What should I do if in the first month I get an eye injury and feel a sharp deterioration in vision, photophobia, watery eyes, a feeling of a foreign body in the eye?

In continuation of the answer to the previous question, I will add the following. Professional help for traumatic dislocation of the corneal flap must be obtained in the next few hours, or in the next few days at the most.

The very medical manipulation is quite simple. Raise the flap, rinse and reattach it. For more information, see the chapter on complications of laser correction.

Is it safe to do laser correction for the second time?

No. When carrying out the first correction, there is a reserve of corneal thickness, so no difficulties are expected. Just like the first time, you have to observe the restrictions.

If you have a very thin cornea, the second step is not possible.

When will I see well after laser correction of my myopia?

The usual answer to this question is as follows.

“In the first three hours you will have lacrimation and photophobia, so during this period there is no time for visual acuity. By the evening, you will already have 60 percent of visual acuity. The next morning about 80%. And within a month they should get your one hundred percent. "

This is not entirely true. For most patients, things are much faster and better. For some, it is longer and worse (then we can talk about the second stage). But such an answer to the question, in my opinion, allows the patient to tune in to the correct attitude to the result of laser correction.

Complications of laser correction

Complications after laser correction?

And they told me ...

LASIK - laser, superficial, outpatient, but surgery. And therefore, she, like all operations, has complications.

LASIK is one of the safest surgical procedures in the world.

The vast majority of LASIK complications can be eliminated. We talked about some of them in the previous chapter. Of course, the patient must be warned about this before correction. Because everything said by the doctor after the correction is considered as an excuse for his own lack of professionalism.

But there are more serious complications of LASIK that reduce visual acuity. The probability of their occurrence is many times less than one percent, but they exist.

This low likelihood of complications is phenomenal for surgery. Therefore, it is not customary for patients to talk about these complications, which, of course, places a great burden of responsibility on the shoulders of the surgeon. There are the following opinions on this question.

In the medical environment, there is an opinion that the patient does not need to know all the nuances of treatment, since he can evaluate them incorrectly and subjectively. And he will refuse treatment, dooming himself with a much greater probability to a more sorrowful fate. Not to mention the need to instill optimism in the patient to create a positive emotional background for treatment. Legally, this is a very shaky position, since according to the consumer protection law, the patient has the right to know all the nuances.

On the other hand, the medical insurance system, which came to us from the West, forces the doctor to familiarize the patient with the possible complications of the surgical operation against signature. There, the doctor does not so much fight for the patient's health and life with all available methods, but rather follows the algorithm prescribed for him in this case by the insurance companies. He is only trying to protect himself and the insurance company from the patient's legal claims. This is a payment for the large salaries of medical workers. As well as the lack of masterpieces is the payment for the big budgets of Hollywood films. So we came to this system. So far only in excimer laser and cosmetic surgery.

Refractive surgeons did not hide the complications of laser correction, but they did not advertise them, trying to justify the promises of advertising with their professionalism. However, now even medical management is coming to the need for broader coverage of these issues. Because the answer to the silence was the rampant growth of rumors about the danger of LASIK. That there are only forums on the Internet about laser correction. A mixture of ignorance and prejudice. True, now there are several professional websites that explain and answer questions from future patients.

Public opinion is inert, and if now the growth of mistrust in laser surgery is not broken, then it will be difficult to make excuses later. I hope this book will help to objectively assess the possibilities of excimer laser surgery and determine its place in the field of medical services.

Complications of PRK

There are different classifications of complications. By time of appearance, by reason of occurrence, by localization. Apparently, in this book the most appropriate classification according to the degree of influence on the result of laser correction.

delayed re-epithelialization;

filamentous epitheliokeratopathy;

corneal edema;

allergy to medications used;

dry eye (mild form).

Complications that require intensive drug treatment to eliminate them, and sometimes repeated intervention to eliminate the consequences:

exacerbation of herpetic keratitis;

dry eye syndrome (severe);

corneal opacity (in other words, haze, subepithelial fibroplasia, or fleur) (mild);

bacterial keratitis.

incomplete removal of the epithelium;

decentration of the ablation zone;

undercorrection;

hypercorrection of myopia;

regression of the refractive effect;

opacity of the cornea (in other words, haze, subepithelial fibroplasia or fleur) (pronounced degree).

Complications of LASIK

Complications that worsen (lengthen, make uncomfortable) the healing period, but do not affect the final result of the correction:

damage to the corneal epithelium with an eyelid expander or when marking;

temporary ptosis (some drooping of the eyelid);

toxic effect on the epithelium of the dye or coloration of the sub-flap space after marking;

debris (remnants of tissue evaporated by the laser under the flap, invisible to the patient and absorbed over time);

ingrowth of epithelium under the flap (not causing decreased vision and discomfort);

damage to the epithelial layer during flap formation;

marginal or partial keratomalacia (resorption) of the flap;

dry eye syndrome (mild).

Complications that require intensive drug treatment for their elimination and sometimes repeated intervention to eliminate the consequences are keratitis.

Complications requiring repeated intervention for their elimination:

improper placement of the flap;

decentering of the optical zone of laser ablation;

undercorrection;

hypercorrection;

tucking the edge of the flap;

flap displacement;

ingrowth of epithelium under the flap (causing decreased vision and discomfort);

debris (if located in the center of the optical zone and affects visual acuity).

Complications for which other methods of treatment are used:

poor quality flap section (decentralized, incomplete, thin, ragged, small, with striae, full flap section);

traumatic damage to the flap (tear or tear of the flap);

dry eye syndrome (chronic form).

A few words about those complications, the elimination of which is possible with the help of repeated intervention.

Debris and ingrowth of the epithelium under the flap

In the process of laser ablation, that is, evaporation of the corneal substance, tiny particles are formed, most of which are released into the air. That's where the smell of "burning" comes from. But a small amount of these particles is deposited back onto the cornea. Of course, the cornea is washed, but some laser ablation products, together with the detachable meibomian glands (glands at the edges of the eyelids), talcum powder from the surgeon's gloves, etc., may remain under the corneal flap. This "garbage" is called debris. Most often, it does not in any way affect the vision and does not bother the patient and gradually dissolves. If the debris is large enough, is close to the center of the optical zone of the cornea and the patient notices it as a speck in the field of view, then the sub-flap space is washed and the flap is re-laid. Nothing special. The same is done when the epithelium (superficial cellular layer of the cornea) grows under the flap.

Ingrowth occurs due to insufficient fit of the corneal flap, its uneven edges, or due to the ingress of cells under the flap during surgery. Cells trapped during the operation are absorbed by themselves. The epithelium, which grows under the edge of the cornea, has a connection with the main layer and receives constant recharge. Therefore, it can grow quite far. This causes a local elevation of the flap, a feeling of a foreign body in the patient, a change in refraction towards the growth of astigmatism. There is no need for additional correction of this astigmatism. By removing this ingrowth, most of the astigmatism will go away. But a relapse is quite possible. The fact is that under an operating microscope, the epithelium is mostly invisible. Therefore, it is quite difficult to remove it all. There are various techniques to exclude relapse, in particular, the use of dyes (staining the entire sub-flap space for a long time), washing the sub-flap space (interface) with a weak dexamethasone solution, and thorough cleaning of the ingrowth site. At the site of ingrowth of the epithelium, it is necessary to de-epithelize a small area of \u200b\u200bthe cornea. The edge of the flap should not be torn, but flat and, therefore, fit more closely to the corneal bed.

Incorrect placement, tucking of the edge or displacement of the flap

With insufficient experience of the surgeon, the flap may be placed incorrectly (unevenly, unevenly). Or the patient may accidentally touch the eyelid and tuck the edge of the corneal flap or dislodge it. In such cases, re-styling is also carried out.

Poor flap cut

In case of a poor-quality flap, the possibility of laser ablation is assessed. If a sufficient area of \u200b\u200bthe corneal bed is exposed, then you can continue to do everything as usual. If there is not enough space, then the flap is neatly placed in place (you can put a contact lens on top for a couple of days for fixation) and after 3–6 months a new cut and a new correction are made. All this concerns the decentralized, incomplete, thin, ragged (botton hole and other options), small flaps and full flap cut.

A striae flap is a flap that has folds. Folds can appear both due to the non-standard work of the microkeratome or the peculiarities of the state of the cornea, and due to mechanical effects on the eye in the first days. If the flap has been displaced, then, of course, it must be re-laid, but the remnants of folds (striae) will remain. Striae can lead to a decrease in the quality of vision due to the occurrence of aberrations (more on this in the next chapter). The second stage of laser correction will help to improve the position.

Decentration of the optical zone of laser ablation.

Undercorrection. Overcorrection

Everyone has heard of nanotechnology. Scientists work wonders by manipulating substances at the molecular level. Supers are required to operate on such a miniature scale. Nanotechnology opens the way for humanity to the future.

But when carrying out laser correction, it is necessary to evaporate the cornea with an accuracy of 1000 nanometers. And for this, equipment is used, which is close in complexity to spacecraft. That is why the accuracy of the excimer laser is checked several times a day - calibrated.

And yet this accuracy is not enough. Each person is too individual. There are several hypotheses explaining the sometimes small discrepancies between the planned and obtained result of laser correction.

For example, hydration in human tissues varies over a fairly wide corridor. You yourself know about this. Some people may experience swelling after sleeping. In the evening, legs may swell, especially in those who stand in one place all day long. Even worse. One person has a loose constitution, the tissues are saturated with water, while the other is dry, thin, and he almost never has edema. And with the cornea, everyone is different. And water absorbs ultraviolet light, including the ultraviolet excimer laser. Therefore, with an equally calculated dosage of laser radiation in a person with a loose, watery cornea, an undercorrection may result, since water will "eat" a lot. And a person with a low density of water in the cornea may experience hypercorrection, evaporate more than planned, micrometers of thickness.

Or there are, for example, scientific papers proving at the histological level the difference in the reaction of the cornea to LASIK. During the formation of a corneal flap and evaporation of the corneal tissue, part of the connective tissue microfibers - collagen fibrils (of which the cornea mostly consists) is removed. Some of the remaining fibrils that have lost one of their attachment sites shrink and thicken. This process is of a centrifugal nature and can lead to a slight (1-2 microns) thickening of the corneal periphery, which has almost no effect on its curvature. Nearly. It is impossible to predict the degree of this influence and the severity of this process individually in each case.

These are just a couple of hypotheses trying to explain the likelihood of undercorrection or overcorrection. There are many more such hypotheses.

However, in practice, such complications are extremely rare and, if they occur, will not ruin your life for the rest of your life. After the correction, your vision will improve in any case. And the second stage of laser correction will help to achieve one hundred percent result.

As for decentration, a lot depends on the intricacies of the diagnostic manipulations performed and the individual characteristics of the location of the optical axis of the eye. The appearance in excimer lasers of systems for tracking the position of the eyeball and new aberrometers with the function of determining not only the center of the pupil and the center of the cornea, but also the localization of the optical axis has almost completely eliminated the possibility of decentration.

The decentering is best corrected with an excimer laser capable of eliminating higher-order aberrations.

Dry eye (chronic)

It would seem a trifle. But this little thing sometimes causes a lot of trouble. It’s not for nothing that so many ophthalmologists have been looking for a solution to this problem in the past five years.

There are many reasons for dry eye syndrome. Ecology, air from air conditioners, stress, increased dryness of indoor air, working at a computer and, of course, increased visual stress.

With prolonged visual concentration, be it driving a car or watching TV, a person really blinks less often. So it was laid by nature. And this state of "drying out" of the eye and a decrease in the production of tears becomes chronic. And then there's the air. And then there is also laser correction, which somewhat disrupts the nervous regulation of tear production. Temporarily. But if you had dry eye syndrome before the correction, then it will not disappear anywhere after. And it will intensify for a while.

We'll have to bury artificial tear preparations, since getting used to them does not develop (and still try to take more breaks when using them).

Keratitis

Keratitis is an inflammation of the cornea, accompanied by pain, decreased vision, severe photophobia and lacrimation. Keratitis can be traumatic, bacterial, viral, neurotrophic and of unknown etiology (cause). Like many other diseases, no one is immune from keratitis. It can occur in those:

who wears contact lenses;

who has the flu;

who blew out;

who got trash in the eye;

who has a toothache;

who has sinusitis;

who got wet in the rain or frozen in the cold.

In academic terms, the etiological factors in the development of keratitis are divided into general and local. Common causes that can cause keratitis include colds (acute respiratory infections, ARVI), sinus infections, caries, tuberculosis, syphilis, etc. Local causes of keratitis are conjunctivitis, small corneal foreign bodies, improper use of contact lenses, trauma and etc.

After laser eye correction, there is a weak spot and any infection in the body can provoke the development of keratitis. The main thing is to diagnose keratitis on time and treat it well. Therefore, before the correction, it is necessary to undergo a general blood test, RW, Hbs Ag, HIV. It is advisable to get advice from a dentist, otorhinolaryngologist and others. In the presence of indolent chronic diseases (from chronic pyelonephritis to stomatitis), the patient should warn the surgeon about them and, if necessary, carry out preventive treatment.

Keratitis that occurs immediately after laser correction is treated with drops and tablets and has no consequences for vision. Usually. But there are also exceptions.

Herpes and fungal keratitis are poorly treatable. If you have had herpetic keratitis before and have decided to do laser correction, then warn the doctor and start preventive treatment on the eve of the operation. The herpes virus, once settled in our body, almost never leaves it. After all, a cold on the lips only for the first time can be an infection transmitted from someone. And in the second and all other times - more often just an exacerbation of the disease due to a decrease in immunity. The same is with the eye - the ultraviolet light of the laser can activate the herpes virus that was dormant in the past in the cornea. In such cases, laser correction should be performed under the cover of appropriate drugs (at least).

As for the treatment of fungal infections, in addition to standard treatment, modern drugs of general antifungal therapy (for example, flucostat) should not be neglected. Invaluable assistance in early diagnosis can be provided by the patient himself, who admitted in time to the presence of chronic fungal diseases that can be localized in any part of the body (otomycosis, mycosis of the feet, etc.).

Complications of LASIK, which can significantly and irreversibly reduce vision

Now in more detail about the complications of LASIK, which can permanently reduce vision. The likelihood of each of them occurring is measured in tenths and hundredths of a percent, and the probability of an irreversible decrease in vision is even less. But this possibility exists.

Traumatic flap injury

Serious traumatic injuries after LASIK are extremely rare. For the first month after LASIK, patients try to comply with the restrictions and avoid even light contact with the eye area. As a rule, they succeed.

In the world ophthalmic scientific literature, there are descriptions of the loss of a corneal flap due to trauma. Of course, an emergency hospitalization is indicated for a patient who has lost a corneal flap. Such an extensive wound of the cornea heals for a long time and painfully. After the end of a long healing process, such a patient has large "plus" diopters - induced, or rather, iatrogenic hyperopia. And a serious decrease in the quality of vision. Further treatment consists in implanting an intraocular lens (artificial lens, IOL) instead of (or together, that is, phakic IOLs) to the patient. The intraocular lens is selected in such a way as to cover the resulting deficiency in diopters and remove iatrogenic hyperopia. A similar operation is performed during the surgical treatment of cataracts. This, of course, is an abdominal operation. But this is a way out of the situation in case of loss of the corneal flap.

Diffuse lamellar keratitis (DLK)

Keratitis has already been mentioned above, but DLK should be distinguished into a separate group.

Diffuse lamellar keratitis (DLK) is insidious in that no one reliably knows the cause of its occurrence and cannot predict and prevent it. On the 2-4th day after LASIK, slight discomfort appears, accompanied by a slight decrease in vision and fog in one eye. Then the gradual progression of these symptoms begins.

Many patients come to do laser correction from settlements, sometimes far away. No need to rush to go back. Even if the doctor permits you. Stay near the clinic that gave you LASIK for about a week. And for any unpleasant symptoms, see your doctor.

If DLK is not started on time with intensive courses of hormone therapy, then you can lose several lines of visual acuity. It is quite difficult to remove the developed opacity under the corneal flap in the optical center of the cornea without consequences.

With DLK, dexamethasone (preferably ophtan-dexamethasone) or 1% prednisolone acetate is required to be instilled into the eye 4–6 times a day (sometimes every hour). The same dexamethasone should be administered under the conjunctiva. Sometimes even general hormone therapy is indicated. In a specialized clinic, a single lavage with dexamethasone under the corneal flap is possible.

For the prevention of DLK, there is still only one piece of advice - it is advisable for allergy sufferers to take prophylactic antihistamines (Kestin, Zyrtec, Erius, Claritin, Loratadin, etc.) on the eve of laser correction and after it for 10-14 days.

There are suggestions that the cause of DLK may be debris, microkeratome lubrication, talc from the surgeon's gloves, which got under the flap during LASIK, but no direct connection with these factors was found. However, it is better for the surgeon to play it safe and not risk it.

Aberrations and their correction

Aberrations

We get the idea of \u200b\u200bthe eye as a perfect optical device since school when studying the section of physics "Optics". When studying the relevant sciences in higher or secondary specialized educational institutions, such an idea of \u200b\u200bthe eye is consolidated, acquiring additional information. Therefore, the statement of S.N. Fedorov that the eye is an imperfect device and the task of the ophthalmologist in improving it was perceived by many doctors with skepticism for a long time.

And what is laser correction if not the improvement of nature's mistakes? Mistakes of nature here include myopia, hyperopia and astigmatism. And not only. Optical scientists have known this for a long time. They knew that when designing even the simplest telescope, it is necessary not only to focus the optical system at one point (exclude myopia, hyperopia and astigmatism of the telescope), but also to ensure the quality of the resulting image. The lenses from which the spyglass is made must be of good glass, almost perfect in shape and with a well-processed surface. Otherwise, the image will be fuzzy, distorted and washed out. That's when the study began aberrations - the smallest roughness and irregularities of refraction. And with the advent of devices for detecting and measuring eye aberrations, a new dimension entered ophthalmology - aberrometry.

Aberrations can be of different orders. The simplest and most famous aberrations are the very same myopia, hyperopia and astigmatism. They are called defocus or second, lower order aberrations. Higher-order aberrations are the very roughnesses and irregularities of refraction that were already mentioned above.

Higher-order aberrations are also divided into several orders of magnitude. It is believed that the quality of vision is influenced by aberrations mainly up to the seventh order. For ease of perception, there is a set of Zernike polynomials that display the types of monochromatic aberrations as a three-dimensional model of refractive unevenness. A set of these polynomials can more or less accurately display any irregularity in the refraction of the eye.

Where do aberrations come from?

Everyone has them. An individual eye refraction map consists of them. Modern devices detect aberrations of a higher order, somehow affecting the quality of vision, in 15% of people. But everyone has individual characteristics of refraction.

The suppliers of aberrations are the cornea and lens.

The causes of aberrations can be:

congenital anomaly (very small and weakly affecting vision, irregularities, lenticonus);

corneal injury (corneal scar tightens the surrounding tissue, depriving the cornea of \u200b\u200bsphericity);

surgery (radial keratotomy, removal of the lens through a corneal incision, laser correction, thermokeratoplasty and other operations on the cornea);

corneal diseases (consequences of keratitis, thorns, keratoconus, keratoglobus).

Ophthalmology is the reason for the attention of ophthalmologists to aberrations. Not paying attention to aberrations and not taking into account their effect on the quality of vision, ophthalmology has existed for quite a long time. Prior to this, only manufacturers of telescopes, telescopes and microscopes studied aberrations and fought against their negative influence.

Operations on the cornea or lens (meaning a corneal incision) increase higher-order aberrations by several orders of magnitude, which can sometimes lead to a decrease in postoperative visual acuity. Therefore, the widespread introduction of artificial lens implantation, keratotomy, and laser correction into ophthalmological practice contributed to the development of diagnostic equipment: keratotopographers appeared, analyzing the refractive map of the cornea, and now also aberrometers, which analyze the entire wavefront from the anterior surface of the cornea to the retina.

LASIK aberrations

Correcting defocus (myopia, hyperopia), the refractive surgeon adds high-order aberrations to the patient.

The formation of a corneal flap by a microkeratome leads to an increase in higher-order aberrations.

Complications during LASIK lead to an increase in higher order aberrations.

The healing process leads to an increase in higher-order aberrations.

Combating LASIK-induced aberrations

It was not possible to remove microroughness and irregularities using a slit-fed excimer laser. A device with the possibility of point ablation was invented and introduced into production, that is, the diameter of the laser beam in some models is less than a millimeter. With the use of Zernike polynomials, computer programs were introduced into practice that allow automatically converting an individual refraction map obtained from an aberrometer in a laser installation into an algorithm that controls a beam that eliminates not only residual defocus, but also higher-order aberrations. Zernike polynomials become a set of tools, each of which is designed to remove a specific component in an aberration complex. Like a carpenter, a plane is for leveling, a chisel is for deepening, a saw is for splitting, an ax is for splitting. It's not that simple, of course. Just as you can find not one, but ten uses for an ax, so the polynomial is designed to remove spatially rather complex shapes. But the basic principle is clear.

When carrying out such personalized laser ablation, the cornea should approximate in shape to the level of an optically ideal sphere.

Supervision

After personalized laser correction, some patients achieved a visual acuity of more than 1.0. The patients saw not only ten lines, but eleven, and twelve, and even more. This phenomenon has been called "supervision".

In scientific circles, a discussion has flared up almost about the violation of human rights. How correct is it to give a person too good vision, because he will see flaws on the faces of loved ones, he will distinguish every pixel on the computer and TV screens, and suffer from an excess of visual information. Quite a scientific approach. Perhaps this dispute will remain relevant in a few years.

However, in parallel with this dispute, commercial proposals appeared. The advertisements for excimer clinics promised supervision to everyone. But supervision is not predictable! Some of the patients will succeed, but dozens of others will not. After all, the ability to supervision is determined by the size of the eye photodetectors, the very cones on the retina. The smaller the cone and the greater its density in the macula, the smaller the object a person can see. In addition, the effect of each type of higher-order aberration on vision has not yet been sufficiently studied. Therefore, a commercial offer of supervision in the form of superLASIK (see above) is incorrect. We can only talk about personalized laser correction.

Effect of aberrations on vision

During the Cold War between the USSR and the United States, scientific and military-industrial espionage became one of the most important areas of work of the special services of the two countries. When the new Soviet MiG fighter demonstrated in local wars a clear advantage of its technical characteristics over enemy aircraft, US intelligence did everything to seize the secret developments of the Artyom Mikoyan design bureau. In the end, they managed to get hold of almost an entire MiG.

One of the advantages of the MiG over its American counterparts was its maneuverability and speed, due to the extremely low air resistance during flight at that time. The air seemed not to resist the aircraft body at all, smoothly flowing around its contour.

To achieve such an effect, American aircraft designers tried to make the surface of their aircraft ideally smooth, flat and streamlined. Imagine their surprise when they saw the uneven, rough surface of the MiG with protruding heads of "rivets and bolts". The secret of the streamlining of the Russian aircraft turned out to be simple and ingenious. All these roughness during the flight created a kind of air cushion around the aircraft body, which allows to reduce the air resistance as much as possible.

Perhaps this is a myth or a legend of aircraft designers, but this analogy perfectly illustrates the attitude of ophthalmologists to higher-order aberrations. The fact is that the views of ophthalmologists on the effect of aberrations on vision over the past ten years have undergone a certain evolution, similar to the evolution of American designers to the characteristics of the surface of an aircraft.

As mentioned above, ophthalmologists have paid close attention to the problem of aberrations mainly due to the deterioration in the quality of vision after corneorefractive surgery. Patients saw the required number of lines, but complained about a decrease in dark adaptation, distortion and blurring of the boundaries of visible objects. There were those who, with practically zero refraction (that is, the absence of myopia and farsightedness), visual acuity did not reach 1-2 lines to the level that they gave in glasses before correction. It is not surprising that the attitude to aberrations was purely negative, as to acquired or congenital pathology. It is this attitude that prompted the race for perfect corneal sphericity and super vision.

Now the opinion of ophthalmologists is changing. The first sign was the legendary ophthalmic surgeon Pallikaris (a world-renowned refractive surgeon and one of the founders of laser correction). In 2001 in Cannes, he suggested that in addition to the parameters of the eye, which are recorded with the help of modern devices, each person also has a “dynamic visual factor”. Time will tell what further research in this area will lead to. One thing is certain: aberrations can both reduce and increase visual acuity.

Perhaps further study of the "dynamic visual factor" will be based on the following hypothesis.

LASIK results in an increase in higher order aberrations. Perhaps narrowing these aberrations to seven orders of magnitude in a research perspective is not entirely correct. The difference in optical density in the interface area (sub-flap space), and the roughness of the resulting surface of the corneal bed, and the healing processes (remodulation of the corneal shape, traction of damaged fibrils, uneven epithelial layer, etc.) are important here. All this, together with other aberrations, leads to blurring of focus on the retina, the appearance of several images. Using the accommodation mechanism, the brain chooses the most clear and satisfying image from all the presented images at a given time period (the principle of multifocality). It is the individual characteristics of the adaptation of the brain to the variability of the resulting image that will be the very "dynamic visual factor" on which it depends - will this set of aberrations improve the vision of a given person or reduce its quality. And this is already associated with the balance of consciousness and subconsciousness, psychomotor peculiarities, intelligence, psychological status ...

From the jungle of assumptions to specific questions. What are the aberrations?

Chromatic, astigmatism of oblique beams, coma, etc. All together they form an image of the surrounding world on the retina, the perception of which is strictly individual for each person. Each of us really sees the world only in his own way. Only complete blindness can be the same for everyone.

There are several types of higher order aberrations.

1. Spherical aberration. Light passing through the periphery of a biconvex lens is refracted more strongly than in the center. The main "supplier" of spherical aberration in the eye is the lens, and secondarily, the cornea. The wider the pupil, that is, the larger part of the lens takes part in the visual act, the more noticeable the spherical aberration. In refractive surgery, it most often induces spherical aberration:

artificial lens;

laser thermokeratoplasty.

2. Aberrations of the angles of inclination of optical beams. Asphericity of refractive surfaces. It represents the mismatch of the centers of the images of the luminous points located outside the axis of the optical system. They are subdivided into aberrations of large angles of inclination (astigmatism of inclined beams) and small angles of inclination (coma).

Coma has nothing to do with the known diagnosis of resuscitators. Its aberrometric pattern is similar to a circle located in the optical center of the cornea and divided by a line into two even halves. One of the halves has a high refractive power, while the other has a low refractive index. With such an aberration, a person sees a luminous point as a comma. When describing objects, people with such aberration use the words "tail", "shadow", "additional contour", "double vision". The direction of these optical effects (aberration meridian) can be different. The cause of coma can be congenital or acquired imbalance of the optical system of the eye. The optical axis (on which the focus of the lens is located) of the cornea does not coincide with the axis of the lens and the entire optical system is not focused in the center of the retina, in the macula. Coma can be, among other things, one of the components of refractive error in keratoconus. During LASIK, a coma may appear as a result of decentering of the laser ablation zone or the peculiarities of corneal healing during laser correction of hyperopia.

3. Distortion - violation of geometric similarity between an object and its image - distortion. Points of the object at different distances from the optical axis are depicted with different magnifications.

Laser correction is not a monopoly in aberration correction. Artificial lenses and contact lenses have already been developed to compensate for some types of higher-order aberrations.

An excursion into the ophthalmic classification of aberrations

Aberrations are classified into three main groups:

diffractive;

chromatic;

monochromatic.

Diffractiveaberrations appear when a beam of light passes near an opaque object. A light wave deviates from its direction, passing near a clear boundary between a transparent medium (air) and an opaque medium. In the eye, such an opaque medium is the iris. That part of the light beam that does not pass in the center of the pupil, but at its edge, is deflected, which leads to light scattering along the periphery.

Chromatic aberrations are due to the following optical phenomenon. Sunlight, as already mentioned, consists of light waves of very different lengths. Visible light ranges from shortwave violet to longwave red. Remember the little bit for memorizing the spectrum of visible light - the colors of the rainbow?

« TOevery abouthotnik fwants snat, rde fromwalking fazan ".

TOred, aboutrank, fyellow, sgreen, rblue, fromother, fiolety.

Each of these types of rays has its own refractive index. Each color is refracted in the cornea and lens in its own way. Roughly speaking, the image of the blue and green parts of the object is focused at the emetron by the retina, and the red ones behind it. As a result, the image of a colored object on the retina is more blurry than black and white. It is on the effect associated with chromatic aberration that 3D video is based.

Monochromatic aberrations, in fact, are the main subject of study of refractive surgeons. It is monochromatic aberrations that are subdivided into higher and lower order aberrations. Low order monochromatic aberrations: myopia, hyperopia and astigmatism. Higher-order monochromatic aberrations: spherical aberration, coma, astigmatism of oblique beams, field curvature, distortion, irregular aberrations.

To describe the complex of monochromatic aberrations of higher order, polynomials of the Zernike (Zernike) mathematical formalism are used. It is good if they are close to zero, and the root mean square deviation of the RMS wavefront is less than 1/14 of the wavelength or equal to 0.038 microns (Marechal criterion). However, these are the subtleties of refractive surgery.

The standard Zernike polynomial table is a kind of set of three-dimensional illustrations of aberrations up to the seventh order: defocus, astigmatism, astigmatism of oblique beams, coma, spherical aberration, trefoil, quatrefoil, and so on, up to eight-leafed (trefoil, tetrafoil, pentafoil, hexafoil ...) ... "Shamrocks" represent from three to eight uniform sectors of a circle with increased optical power. Their occurrence may be associated with the main centripetal directions of the stromal fibrils, a kind of corneal stiffeners.

The aberration pattern of the eye is very dynamic. Monochromatic aberrations mask chromatic aberrations. When the pupil expands in a darker room, spherical aberrations increase, but diffraction aberrations decrease, and vice versa. With age-related decrease in the ability to accommodate, higher-order aberrations, which were previously a stimulus and increased the accuracy of accommodation, begin to reduce the quality of vision. Therefore, at present it is difficult to determine the significance of the positive and negative effects of each type of aberration on the vision of each person.

The role of aberrometry (with keratotopography function) in preoperative examination

Everything has already been said about this. According to the aberrometry data, an individual map of the wavefront is compiled, according to the parameters of which personalized laser correction is carried out. In most patients, the level of higher-order aberrations is very low, to put it mildly. And there is no need to use personalized laser ablation. Autorefractokeratometry data are sufficient. But that doesn't mean you shouldn't chase personalization. After all, if you have aberrations, then they can only be detected by aberrometry. And with the correction, you are more likely to get a higher visual acuity than you have ever had with glasses or even contact lenses.

Figure: 17.

Eye wavefront analyzer (aberrometer with keratotopography function). The essence of keratotopography is as follows. Luminous concentric circles (Placido disc) are projected onto the anterior surface of the cornea (b)and their reflection is photographed by the apparatus (a)... Based on the difference between the parameters of the projected and reflected circles, the apparatus calculates the curvature of the cornea at 10,000 points and forms a refraction "map"

Personalized laser ablation is also performed with additional correction, with correction after other operations and with a thin cornea.

As for the diagnosis as such, that is, the search for pathology, the main thing here is not to miss keratoconus.

Keratoconus again

It is quite easy for a refractive surgeon to identify keratoconus with the appropriate equipment. But that’s not the problem. The problem is responsibility. As well as the complexity of the sapper's work, not only in the knowledge of the intricacies of the craft. The difficulty is that the sapper is wrong only once. You can't be wrong with keratoconus. Never. And for this you need to constantly keep in mind its indirect signs:

myopic astigmatism often with oblique axes;

the optical power of the cornea is more than 46 diopters;

thin cornea;

surprisingly good vision without glasses and surprisingly poor with glasses in the presence of pronounced astigmatism;

progression of astigmatism;

local protrusion of the cornea, often in the lower sector.

This protrusion cannot be missed in keratotopography (or aberrometry). The protrusion is accompanied by an increase in optical power. The generally accepted standard of color indication colors in the image of the wavefront blue areas with a lower optical power (diopter), and red - with a higher one. Classic keratoconus looks like a red spot in the lower right or lower left cornea.

By the way, ordinary high-grade astigmatism looks like a red butterfly. Sometimes the wings of this butterfly lose their symmetry. One wing becomes huge, shifts downward, and the other decreases. Like sand in an hourglass, optical power flows from the top to the bottom. This may already be a manifestation of keratoconus. In this case, laser correction cannot be performed (see chapter 6).

Who tolerates the aberrations acquired after LASIK worse?

Young people with a labile psyche and a wide pupil. Each of us has a different pupil size in the light. On average, three millimeters, but some have a couple of millimeters more from birth. And the larger the pupil, the larger the area of \u200b\u200bthe cornea and lens that takes part in the act of vision. And the more small roughness distorts the image. As a rule, the brain does not pay attention to such little things. Just as it excludes floating opacities in the vitreous body from visual information (most of myopic people have them), and a person pays attention to them only sometimes, looking at blinding white snow or, say, at a light computer screen. But in subtle, creative, nervous natures, perception is often heightened, and this can contribute to the fact that they constantly pay attention to such stimuli. This is not picky, but a feature of the nervous system, such as the individual threshold of pain sensitivity.

In such cases, you can try to develop an addiction to aberrations in the brain, or rather, to divert its attention from this problem by instilling drops that constrict the pupil (pilocarpine) for a month. If this tactic fails, it will be necessary to make additional corrections in order to reduce the higher-order aberrations.

Where in everyday practice can the optometrist encounter higher-order aberrations?

With keratoconus, visual acuity with full spectacle correction often falls short of 1.0. When examining vision through a diaphragm of three millimeters or less, visual acuity is significantly improved (see above). In both cases, the reason for what is happening is in aberrations.

After cataract removal with implantation of an artificial lens, the patient often, even with full spectacle correction, does not see 1.0. Not in all cases it is associated with retinal diseases, amblyopia or secondary cataract.

Artificial lens with a smaller diameter than natural. Sometimes the artificial lens can be uneven. During the operation, a corneal incision changes the spherical shape of the cornea. All these reasons cause higher-order aberrations. In extreme cases, they can be reduced by performing personalized laser correction (more on bioptics in the next chapter).

It makes sense to carry out aberrometry and with the so-called night blindness, manifested by deterioration of visual acuity at dusk, but not accompanied by signs of serious retinal diseases (tapetoretinal abiotrophy, etc.).

There are many examples. If aberrations are suspected, the patient can be referred for examination at a refractive surgery center.

Surgical nuances

Various aspects of laser correction are discussed in scientific papers, in speeches at conferences and in other types of professional communication of ophthalmologists of the world with each other. Such communication is extremely informative and has a great impact on the growth of the quality of medical services provided. But there is one area that is almost not at all touched upon during such communication - the practical features of LASIK. Such characteristics are usually passed from teacher to student during the training of the profession already in the workplace. The final result of laser correction most often does not depend on them, but it is they who create the individual style of each surgeon, each clinic. The accumulation of small pieces of practical knowledge over time leads to the emergence of new methods, tools and ways of development. Quantity turns into quality.

Unfortunately, in Russia there is no single laser correction training center that would accumulate such nuances of the practical work of refractive surgeons in its work.

Several features of LASIK using the standard technique are presented in this excursion.

Calculation of laser ablation parameters

1. When an excimer laser system is purchased by the manufacturer in combination with the equipment, as a rule, computer programs are supplied that automatically convert the aberrometry data of each patient into a spatial algorithm for laser ablation. This algorithm includes three stages:

elimination of spherical ametropia;

elimination of cylindrical ametropia - astigmatism;

elimination of the irregular component of refraction - monochromatic aberrations of higher order.

In most patients, the third stage is either absent or takes an extremely insignificant fraction of the total planned laser ablation depth. With a small assumed depth of laser ablation in the third stage (say, less than 3 μm), it is advisable not to exclude its implementation during LASIK. A slight irregularity not only does not significantly affect the postoperative visual acuity, but in general can be an error in the aberrometry associated with tear redistribution.

The fact is that the distribution of tears over the surface of the cornea during an ophthalmological examination has a rather significant negative effect. The instillation of drops that dilate the pupil irritates the mucous membrane of the eye and contributes to a change in the normal production of tears. Especially in those patients who have a long experience of wearing contact lenses. In addition, during the aberrometry, the doctor asks the patient not to blink for a couple of seconds. Against the background of the instillation of drops, a couple of seconds is often quite enough for an unpredictable and uneven redistribution of tears on the surface of the cornea, up to the appearance of "dry spots" - zones of complete drying of the tear film on the cornea. In such conditions, an increase in the reliability of aberrometry can be achieved by a mandatory request to the patient to blink several times right before the study. It is also desirable to carry out aberrometry at least twice in each eye. When calculating the parameters of laser ablation, a comparison of the values \u200b\u200band contours of the third stage, calculated on the basis of two or more studies, will make it possible to evaluate the reliability and value of the obtained measurements of higher-order monochromatic aberrations.

2. There will certainly be a slight difference between the values \u200b\u200bof ametropia obtained by autorefractokeratometry and aberrometry. The difference in parameters is primarily associated with the diameter of the investigated zone. In an autorefractometer, the study area is mainly 3 mm, and in an aberrometer it is much larger. That is why it is "two big differences" to evaluate the LASIK refractive result using aberrometry data and autorefractometry data. And which one is more correct will determine only the patient's visual acuity and quality.

3. Previously, only one parameter was considered the guarantee of the absence of halo effects - the diameter of the optical zone of laser ablation. The larger the optical zone, that is, the larger the correction zone of the refractive index on the cornea, the less chances of negative changes in the quality of vision in conditions of a wide pupil (twilight, incomplete darkness). Now priority is given to another parameter - the gradual transition from the optical zone to the surface of the cornea that has not been exposed to laser action (transient zone). The profile of the transient zone in modern excimer lasers can have more than seven gradations - from a sharp transition, which has to be resorted to with a thin cornea with a high degree of ametropia, to a very smooth transition, which significantly reduces the likelihood of unwanted light effects. However, to obtain a favorable profile of the transit zone, it is necessary to increase its duration. An increase in the duration of the transient zone leads to a decrease in the optical zone. The recommended ratio of the diameters of the optical and transient zones is 5.5 mm, 7.5 mm and more. But with the forced choice of a sharp transition from the optical to the transient zone, it makes sense to increase the size of the optical zone and reduce the size of the transient zone. This is the surgeon's choice.

4. The size of the transient zone must be calculated taking into account the planned size of the corneal flap. With a small diameter of the cornea and its high curvature, a flap of a smaller diameter is formed during the operation.

For example, if the diameter of the flap is planned to be 8.5 mm, then the size of the transient zone should be no more than 7.5 mm. And given the possibility of a slight decentering of the flap or inconsistency of its actual diameter with the planned one, it is desirable to reduce the size of the transit zone to 7 mm.

LASIK stages

1. After placing the patient on the operating table, a pulse oximeter sensor is usually put on his finger, which allows real-time monitoring of the patient's pulse rate and the level of oxygen in the blood. Increasing the heart rate up to 100 beats per minute or more can be considered a natural reaction of a person in a stressful situation. But if the pulse is less than 60 beats per minute, then this should alert the doctor. A pulse rate of less than 50 can be considered a relative contraindication to laser correction. The most common two causes of a rare pulse (bradycardia): left ventricular hypertrophy of the heart in people who previously went in for sports (athletics, running, skiing, etc.), and a tendency to faint (collaptoid state) against a background of stress. If bradycardia with left ventricular hypertrophy can be equated to the normal variant, then bradycardia as a harbinger of fainting (collapse) during laser correction is an undesirable phenomenon.

Therefore, when the heart rate decreases, the doctor is advised to start a conversation with the patient, during which he should try to calm him down. The doctor's speech should be calm, confident and unhurried. The timbre of the voice is as low as possible. You must empathize with the patient. It is worth expressing regret that he is so worried and promise no pain. You can put your hand on his forehead or on the temporal areas (through sterile tissue, of course). If during this treatment within 5-10 seconds the pulse increased to 70-80 beats per minute, you can begin to operate. During the operation, the heart rate must also be monitored. The most important in this sense is the moment of applying the vacuum ring. If its imposition provoked an increase in the heart rate, then this is a favorable reaction of the body. However, sometimes (extremely rarely) an increase in intraocular pressure against the background of the imposition of a vacuum ring can lead to a drop in the pulse rate. Such a reaction can be caused, for example, by the presence of a pathological oculocardial reflex in the patient. Oculocardial reflex is an atypical reaction of the nervous system to pressure on the eyeballs, manifested in a slowdown in the heart rate. With such a reaction and other fainting conditions, it is better to temporarily interrupt the laser correction in order to calm the patient. With an initially rare pulse (less than 50), for the prevention of syncope, it may be advisable to prescribe a preoperative subcutaneous or intravenous administration of atropine 0.1%, about 0.5 ml, or other medication, starting with tincture of valerian or motherwort.

Considering that the cause of a rare pulse can be an incipient minor epileptic seizure, a post-infarction state, and a previously not diagnosed heart rhythm disturbance, it is desirable to have an anesthetist in the operating unit. Not all patients can easily tolerate the stress associated with waiting for the operation, and the anesthesiologist will help them cope with various negative reactions of the nervous system.

2. Applying an eyelid dilator (blepharostat). The first meeting of the patient with the instruments. It is desirable that this meeting be held "on a friendly footing." The painful sensation at the beginning of LASIK will contribute to the involuntary compression of the eyelids throughout the entire operation, that is, constant pain. This will not only reduce the patient's ability to control the fixation of his own gaze, but will also somewhat narrow the palpebral fissure, thereby complicating the rest of the manipulations. Painful sensations during the application of the eyelid dilator are facilitated by the touch of the cornea to the branch and the reflex spasm of the eyelids.

Touching the cornea to the branch of the blepharostat is possible if the patient is not completely self-controlled. In such a patient, when the doctor touches the upper eyelid, the eyes begin to "run" in different directions with a tendency to roll up. You can additionally drip anesthetic drops into the eyes and try to calm the patient. Calm, confident and unhurried speech of the doctor can "work a miracle" here too.

After insertion of the branch on the lower eyelid, a reflex spasm often follows. Failure to close the eyelids of one eye can even trigger panic in some patients, triggering a vicious cycle of excitement: panic? increased spasm of the eyelids? an increase in pain? panic. To avoid such a cycle, it is recommended to widen the palpebral fissure gradually and between bouts of eyelid compression. When using a spring blepharostat, lead to its maximum pressure gradually, and with a screw blepharostat, achieve the required width of the palpebral fissure in three or four steps. If a closed cycle of excitation does occur, you can release the pressure of the jaws on the eyelids and calm the patient. You cannot drip anesthetic drops at this moment. A reflex defense reaction to liquid entering the eye will only increase eyelid spasm.

3. It is necessary to apply a vacuum ring of a microkeratome taking into account the location of the visual axis. For this, the patient must look at the gaze fixation point. However, with a small diameter of the cornea, such a location of the ring can lead to unilateral damage to the pericorneal vessels during cutting. With a small cornea, it is better to apply the ring at an equal distance from the limbus.

4. Before cutting, the surface of the cornea must be moistened, because local de-epithelialization or even perforation of the flap may occur in the drying areas.

During the formation of the corneal flap, it is advisable not to rely entirely on the automatic stopper of the head movement, but to control the degree of cut with a glance. Unfortunately, this is not possible in all microkeratome models. Visual control allows you to stop the movement of the head of the microkeratome if there is a risk of a complete cut of the flap. In rotational microkeratomes, there is more opportunity to notice the risk of a complete cut in time than in linear ones, since the stopper goes around a circle centered at the optical axis of the eye and its path is longer (half the circumference is larger than its diameter, which gives the surgeon more time to react to the appearance of full cut risk).

The advantages of automatic microkeratomes over manual ones are as significant as the advantages of manual ones over automatic ones.

Some microkeratome models have a reduced vacuum level that is used to manually center and hold the eyeball in position during laser ablation. However, the vacuum ring and its handle can interfere with the automatic eye tracking (auto tracking) system. And the patient's eye is self-centered much more accurately (just by looking at the fixation mark) than with a ring. So now the level of reduced vacuum is used much less often. For example, if the patient has congenital nystagmus (involuntary rhythmic eye movements).

5. Fixing the patient's gaze on the desired mark is critical when performing laser ablation. If the patient fixes his gaze incorrectly, this will lead to decentering of the ablation zone and the need for a second stage of correction.

To illustrate, we can give a possible algorithm for communicating with a patient in a situation where it is necessary to fix the patient's gaze on a red mark, that is, on the beam of a directing laser (diode or helium-neon).

Doctor:

A patient: This is not the point.

Doctor: Yes. It is rather a red spot. Can you see him?

A patient: Yes.

Doctor:

Such a dialogue is most favorable. He proves that the patient is adequate enough and sees the mark that needs to be looked at. The doctor knows that the patient's vision is very blurry when the corneal flap is folded back. He sees the red dot as a large, uneven, blurred spot. The doctor deliberately provokes the patient into an imaginary argument about the absence of a point, checking the adequacy and attentiveness. But another turn of the dialogue is also possible.

Doctor: Please look at the red dot.

The patient is silent.

Doctor: Do you see the red dot?

A patient: Yes. This is not the point.

With such a development of the dialogue, doubts arise about the sufficient level of patient care. But the answer "This is not the point" indicates a return of attention.

Doctor: Please look at the red dot.

The patient is silent.

Doctor: Do you see the red dot?

A patient: Yes.

Doctor: It is more likely not a dot, but a red spot. Yes?

A patient: Yes.

Doctor: Look only at the center of the red spot. Do not drive with your eyes. There will be a crackle now. Don't be alarmed. It's just a harsh sound.

Here, the doctor has doubts about the patient's ability to clearly follow the instructions. The risk of the eye moving away from the desired position during laser ablation increases. The doctor should be alert and, perhaps, re-instruct the patient, warning him about the need not to look away from the red mark.

If the patient does not answer the doctor's questions, the laser correction cannot be continued.

6. Landmarks for centering the laser ablation zone can be different. In principle, the center of the ablation zone should be located at the point at which the cornea crosses the optical axis of the eye. However, it is sometimes quite difficult to determine this point during laser correction even if the main condition is strictly observed - fixing the patient's gaze on the light mark. The point of intersection of the cornea with the optical axis of the cornea does not coincide with the anatomical center of the cornea and pupil, therefore such landmarks can only be used for approximate centering.

There is another way to roughly determine the center of the ablation zone. The red beam of the aiming laser, when it coincides with the optical axis of the eye, is reflected from the macula strictly perpendicular to it, which leads to the appearance of reflection, speckle, and a halo around the beam. However, such a reflection can appear when the beam is reflected not only from the macula, but also from the paramacular region of the retina.

In modern computer programs for calculating the parameters of laser exposure according to aberrometry data, there is a special function that allows you to determine the location of the point of intersection of the cornea with the optical axis of the eye relative to the anatomical center of the cornea. But this method is only advisory in nature, since it is impossible to completely repeat the position of the patient's head both during aberrometry and during laser correction. And the localization of the anatomical center of the cornea is not always reliable.

Determination of the center of the laser ablation zone is often indicative. However, when correcting myopia and myopic astigmatism, this is not of fundamental importance. The zone in which refractive changes after myopic ablation are equally satisfactory has a diameter of one millimeter or more (depending on the degree of myopia). Therefore, an error in the centering of the ablation zone of several tenths of a millimeter will not lead to significant consequences for postoperative visual acuity.

Another thing is laser correction of hyperopia. Ideally, the apex of the cone-shaped protrusion of the corneal surface formed by the excimer laser should coincide with the optical axis of the eye. Even slight decentering of the ablation zone can lead to residual complex hyperopic and irregular astigmatism. This is one of the many disadvantages of excimer laser correction of hyperopia and hyperopic astigmatism.

7. Before performing laser ablation, it makes sense to pay attention to the parameters of the formed corneal bed. In the optics of the operating microscope built into the excimer laser there are marks that allow roughly (!) To estimate the size of the planned laser ablation zone and its location. If, due to some decentration of the corneal flap (and, accordingly, the corneal bed) or its insufficient size, the border of the planned ablation comes close to the edge of the bed and even protrudes beyond it, then it is necessary to change the settings of the excimer laser and reduce the transient and optical zones. If this condition is not met, undercorrection and refractive regression are likely to occur.

8. It is undesirable to interrupt laser ablation. The reason for the temporary interruption of ablation is either a misalignment or an obstacle that prevents the delivery of the laser beam to the surface of the corneal bed.

The misalignment in modern lasers occurs mainly when auto-tracking, a system for automatically tracking the position of the eyeball, fails. Such a system is not only capable of moving the head of the excimer laser with sufficient speed following small movements of the eye, but at the same time it can itself identify the center of the cornea and establish the zone of the proposed ablation relative to it. However, the surgeon should not completely rely on this beam positioning. The position of landmarks, and hence the parameters on the basis of which the auto-tracking system works, can distort or completely hide the following factors.

Excessively wide pupil. In most cases, this problem can be easily solved by increasing the brightness of the operating field illumination. Even with residual drug mydriasis, the pupil reacts to light, slightly decreasing in diameter. With complete drug mydriasis, it is better to postpone the laser correction.

Getting into the "field of view" of the auto-tracking system of a foreign object - a swab, a napkin or even a patient's nose, etc. It is necessary to remove interfering objects. In the case of the nose, it is advisable to slightly turn the patient's head to the side, thereby moving the back of the nose away from the operating field.

Pronounced roughness of the surface of the corneal bed after drying. It is recommended to manually center the laser. Most often, after 3–8 laser pulses (scans) have been carried out, the rough surface ceases to “glare” and auto-tracking is already capable of working (during laser ablation, several dozen scans are performed, sometimes more than a hundred). However, there is also the opposite situation - decentering of the laser beam during ablation due to erroneous re-centering of auto-tracking under the influence of an extraneous light flare. Timely identification and correction of such a failure allows constant visual control of the auto-tracking by the surgeon.

Even in the absence of the listed reasons that disrupt the operation of auto-tracking, you should control its operation. Disruptions to the auto-tracking operation may appear that are absolutely not related to the factors listed above. Starting from various design features of the system or software failures, ending with defects in the rules for operating the device.

The appearance of an obstacle that interferes with the delivery of the laser beam to the surface of the corneal bed and forces the interruption of the laser ablation is meant:

Getting into the area of \u200b\u200bablation of the tupfer. This can not only disrupt auto-tracking, but also lead to irregular postoperative astigmatism. And the point here is not so much in the accidental and fleeting hit of the tupfer in the center of the operating field, but in deliberate and long-term manipulation for the forced permanent draining of the corneal bed.

A sudden movement of the patient's head in response to a loud sound.

The appearance of the patient's hands in the area of \u200b\u200bthe operating field. Such an emergency situation forces not only to interrupt ablation, but also to repeat all aseptic and antiseptic measures, including the treatment of the operating field and the surgeon's hands, replacement of instruments, etc.

The release of the patient's eyelids from the jaws of the eyelid dilator, accompanied by blinking movements.

Spontaneous fall of an insufficiently fixed corneal flap onto the corneal bed.

Penetration of fluid onto the surface of the corneal bed undergoing ablation.

9. Even with auto-tracking, constant visual control over the process of laser ablation is required. The purpose of such control is, first of all, early fixation of the moment when a layer of fluid appears on the surface of the corneal bed. The fluid on the surface of the corneal bed is formed from:

residues of medications instilled into the conjunctival cavity and on the surface of the cornea;

blood leaking from the damaged pericorneal network;

fluid released from the cornea during ablation.

From the conjunctival cavity, fluid enters the surface of the corneal bed most often from the side of the flap leg. At this point, the fold of the corneal flap forms a kind of capillary, into which fluid enters through the gap formed by the anterior surface of the cornea and the conjunctiva. Sometimes it is required to regularly or continuously drain this capillary with a dry swab, even during ablation. The same measures have to be taken when blood seeps from the damaged pericorneal network. Damage to the pericorneal network occurs quite rarely and is due to:

very small diameter of the cornea;

pronounced difference between the vertical and horizontal diameter of the cornea;

germination of blood vessels into the cornea with prolonged wearing of contact lenses.

It is not difficult to notice the appearance of a layer of liquid. During ablation, the surgeon sees a shimmering blue spot on the surface of the corneal bed. The appearance of a layer of liquid is visualized as an unexpectedly appearing and centripetally spreading "puddle" in the area of \u200b\u200bthe flickering spot. Changes in the brightness and uniformity of the spot, as well as the volume of the accompanying sound (crackling) are additional signs of the appearance of liquid.

If a layer of liquid appears on the surface of the corneal bed, it is necessary to immediately stop the laser ablation and remove it with a dry swab. The liquid absorbs most of the energy from the excimer laser beam, which can lead to residual ametropia and irregular astigmatism.

Postoperative patient management

1. In the first days after the correction of hyperopia, the patient's refraction is usually "minus". Postoperative myopia or mild myopic astigmatism is not only a prognostically favorable refraction, but even a desirable one. Refractive regression after correction of any degree of hyperopia occurs in the vast majority of cases. And early myopic refraction allows the final, distant, stabilized, long-lasting result of laser correction of hyperopia to come closer to emmetropia.

2. Weak myopic refraction after laser correction of myopia is most comfortably tolerated by the patient. However, it is all about the magnitude of residual ametropia. Sometimes even residual myopia of –0.75 diopters reduces the patient's visual acuity by 0.1–0.3. Therefore, even super weak myopia on the first day after laser correction deserves attention.

The algorithm of the doctor's behavior is as follows. First, look at the degree of accommodation spasm during the preoperative ophthalmological examination (that is, the difference between refraction without cycloplegia and with cycloplegia). The approximate coincidence of the size of the accommodation spasm with postoperative refraction will be an additional argument in assessing the results of correction as satisfactory. Especially with high visual acuity without spectacle correction.

But if the visual acuity without spectacle correction is slightly lower than planned, the refraction is 1.0 diopters or more (with a slight spasm of accommodation according to the preoperative examination data), and at the same time astigmatism is detected, then we are talking about undercorrection, most likely due to decentering of the laser zone. ablation. It is possible to establish more reliably signs of decentration using aberrometry. In any case, in case of true residual myopia, it is recommended to prescribe instillation of medications that reduce the level of intraocular pressure for 1-2 months. The same prescription should be given if there is an increased risk of refractive regression associated with thin corneas or high myopia.

Prescribing such drugs not only reduces the degree of possible side effects of glucocorticoids, but also reduces the pressure on the cornea from inside the eye. This is not a common purpose. There is no evidence that IOP contributes to corneal remodulation leading to refractive regression. Rather, on the contrary, there is more evidence that a persistent increase in the cell layers of the epithelium in the places of postoperative "depression" of the outer surface of the cornea is more to blame for the refractive regression. But doctors came to the appointment of such drugs empirically and, in any case, there is no harm from them.

By the way, in order to reduce the normal level of intraocular pressure, it is better to use not drugs that improve outflow (arutimol, etc.), but drugs that reduce the production of intraocular fluid, or combined drugs (betoptic, etc.).

3. A refractive surgeon should not consider additional correction as the best way to meet the claims of a patient who is dissatisfied with the result of laser correction. Especially with hyperopia. Despite the thick cornea and shallow depth of laser ablation, each additional correction for hyperopia increases the risk of developing iatrogenic keratoconus. And the calculations have nothing to do with it. This information was obtained by doctors thanks to the injured patients and cannot be neglected. The quality of vision after excimer laser correction of hyperopia is not satisfactory enough, but additional correction does not always help in this. This is another argument against the correction of hyperopia, not only high, but, at times, and moderate.

There are many surgical nuances (some of which are listed in this chapter). Some of them improve the quality of laser correction results, others are only characteristics of the doctor's individual handwriting, and still others, over time, may turn out to be biases that do not matter. But such little things are worthy of attention, if only because they can serve as small steps in improving the skills of a surgeon.

Refractive surgery innovations

Numerous new methods of diagnosis and treatment appear in ophthalmology every year. In a few years, everything stated in this chapter may become a common place, an integral part of the work of most ophthalmological clinics. And some innovations will be recognized as unnecessary in clinical practice and will be used only in research activities.

Diagnostic equipment

Keratotopograph with 3D image of the anterior segment of the eyeball (Pentacam)... It allows not only to study the refraction of the anterior and posterior surfaces of the cornea, but also to carry out non-contact pachymetry (determination of the thickness of the cornea), to determine the optical density of the lens, to measure the angle of the anterior chamber and generally gives a three-dimensional image of the anterior chamber. The apparatus does not provide any new characteristics for refractive surgery. The same keratotopography as usual. The diagnosis of keratoconus is perhaps more indicative. Not only local enhancement of refraction, but also the place of corneal protrusion in the sagittal plane, that is, in profile, and pachymetry at the apex of keratoconus. At the same time, more detailed diagnostics of the iris and lens during the preoperative examination.

Optical scanners... There are a great many of them. Here are just a few:

laser scanning confocal ophthalmoscope (retinotomograph HRT);

optical coherence tomograph (Stratus OCT);

scanning laser polarimeter (GDx VCC);

retinal thickness analyzer (RTA).

Their main purpose is digital analysis of the state of the retina. After laser correction, the thickness of the cornea decreases, which makes it difficult to determine the true intraocular pressure. In such a situation, you may not notice the development of glaucoma. Scanners can diagnose glaucoma regardless of pressure measurement (i.e. glaucoma and low blood pressure). They reveal the smallest changes in the optic nerve head, bending under the action of increased intraocular pressure in glaucoma, or corresponding changes in the thickness of the retina.

Moreover, the first two scanners have modifications that allow examining the cornea. The HRT laser scanning ophthalmoscope has a corneal module that allows confocal microscopy of the cornea. And the optical coherence tomograph has models that allow you to take pictures of the cornea in the sagittal plane. This makes it possible to measure not only the thickness of the cornea, but also, for example, the thickness of the corneal flap or to estimate the depth of the leucorrhoea, etc. Such a device can be used not only for preoperative examination, but also for postoperative dynamic monitoring of the state of the cornea after corneal refractive surgery (including LASIK) ...

Confocal microscope... Such a microscope can be either a separate device (Confoscan) or a laser scanner module (Rostock HRT retinotomograph module). Its function is the intravital histology of the cornea and other tissues of the anterior segment of the eyeball. The device practically does not touch the eye, but the cornea at the cellular level becomes visible on the computer monitor. You can determine the density of cells of the epithelium, stroma or corneal endothelium (HRT), or measure the thickness of the same corneal flap. And much more.

HRT has proven itself well in the postoperative follow-up of LASIK, in the diagnosis of hereditary corneal dystrophies, in the determination of indications for phototherapeutic treatment of leucorrhoea. And as for the diagnosis of glaucoma with low pressure, it is generally called the "gold standard". However, in fact, the spectrum of its clinical application has not yet been fully determined and is in the development stage (see the book "Laser tomography of the eye: anterior and posterior segment". Aznabaev BM and others).

Analyzer of the biomechanical properties of the cornea.If a refractive clinic does not have an optical scanner for diagnosing glaucoma, then the clinic must have an analyzer of the biomechanical properties of the cornea.

Several years will pass and people who have undergone laser vision correction, for the most part, will reach the age of forty. After forty years, all people are at risk of developing cataracts and glaucoma. In order to detect glaucoma in time, everyone at this age needs to measure intraocular pressure at least once a year. Those who have done laser correction should have their blood pressure measured at refractive clinics. The only device that will show the true pressure in people with a thin cornea (and too thick, by the way, too) is an analyzer of the biomechanical properties of the cornea.

New in laser correction

Excimer laser systems are constantly being improved, but there are almost no revolutionary innovations. Of course, if we consider it not new, but quite standard, personalized laser correction, an automatic eye tracking system, a point supply of a laser beam and a ventilation system of the operating field (evacuation of ablation products with a structure similar to a microvacuum cleaner). The principal innovations at the moment are the femtosecond laser, epimicrokeratome and excimer laser correction of presbyopia. These novelties did not appear in the past or the year before last, but their introduction into clinical practice begins only now.

Femtosecond laser

The femtosecond laser allows the formation of a corneal flap without the use of a microkeratome, as well as intracorneal canals for the implantation of intracorneal rings.

The advantage over the microkeratome lies in the ALMOST contactless manipulation, the absence of the need to create a vacuum, which increases the intraocular pressure up to 50 mm Hg. Art., and increased control over the formation of the corneal flap.

The disadvantage is the very high price of the device, comparable to the cost of an excimer laser, the duration of the procedure and a less smooth surface of the corneal bed. The last two factors are technically removable in the process of improving the device, but its cost will not significantly decrease in the near future. Three years ago, it was believed that the femtosecond laser would never enter widespread clinical practice. However, now quite a few refractive clinics in the United States have acquired the device and made it one of the main arguments in the competition. In Russia, femtosecond lasers have appeared in Moscow and Cheboksary.

Despite the minimal advantages of a femtosecond laser over a microkeratome, the growth of competition in the refractive services market can lead to the widespread introduction of devices into practice in our country. True, manufacturers of microkeratomes also do not give up, constantly improving their products. The femtosecond laser does not yet have a fundamental advantage over the microkeratome.

Epimicrokeratomas

The names of these devices may be different, but the essence is the same. A fairly large number of patients with contraindications to LASIK (most often it is a thin cornea) remains "uncovered" by modern refractive surgery. This became the main motivation in the search for a method that combines the advantages of PRK and LASIK and does not have their disadvantages. A compromise can be considered a microkeratome capable of forming a corneal flap about 50 μm thick, consisting only of the corneal epithelial layer. The method is called EpiLASIK. The indications for it are only growing so far, but time will tell how much it will be spared the disadvantages of PRK (pronounced regression of the refractive result with medium and high ametropia, haze - corneal opacity). Its two definite advantages over PRK are the reduction of the period of discomfort after surgery (not without the help of a contact lens at first) and the healing process. And the advantage over LASIK is the ability to perform correction even with an ultrathin cornea (but not with high ametropia).

Excimer laser correction of presbyopia

Presbyopia is age-related hyperopia (see Chapter 1). There have been many attempts at surgical correction of presbyopia. But they all ran into two difficulties. First, it is difficult to improve near vision without impairing distance vision. The second is that presbyopia is always progressing, adding diopter with each passing decade and thus leveling the effect of any correction.

Now, using a point feed of a laser beam, they are trying to turn the cornea into a multifocal lens, that is, a lens with several focuses. Several images are also formed on the retina, and the brain selects from them the image that is clearer at the moment. You need to look at something close - the brain chooses a focus, which gives a clearer image up close. You need to look into the distance - the brain chooses another image that is more suitable for this goal.

This is achieved by various algorithms for personalized laser ablation. There are ideas about a stepped cornea and a dosed decentration of the ablation zone. And much more. Further research will show how effective and long-term this will be.

Alternatives to LASIK. New methods of surgical correction of myopia, hyperopia and astigmatism

Now the question of an alternative to LASIK arises mainly when there are contraindications to laser correction. Other methods are either more risky, or their result is less predictable, less accurate.

Transparent lens aspiration (APC). Phakic and multifocal IOLs. Bioptic surgeries

With very high myopia or hyperopia, it is pointless to do LASIK. Diopters will decrease, but there will be quite a lot of them, and the patient will not be able to do without glasses, although their optical power will significantly decrease.

Since there is no way to change the cornea, then you should think about changing the lens. It is not possible to simply decrease or increase the optical power of the lens. With any damage to the outer capsule, the lens becomes cloudy - a traumatic cataract develops. Therefore, there are two ways out: either remove your transparent lens and implant an artificial lens in its place (intraocular lens - IOL), or place a phakic IOL next to your lens. Operations similar to the first are performed when removing a cataract. But here it is removed, aspirated (sucked out through a microtubule) not a cloudy, but a transparent lens.

The terminology is as follows.

Afakia - an eye without a lens (this was done before, now only in severe cases).

Artifakia - an eye without its own lens, but with an artificial one.

A phakic IOL is an artificial lens that is inserted into the eye without removing its lens.

The advantages of these techniques are that you can remove almost any degree of myopia or hyperopia, and in the presence of toric IOLs - and astigmatism.

The disadvantage, like any other abdominal surgery, is the possibility of serious complications. Of course, every clinic tries to reduce the risk to zero, and it almost succeeds. The risk of losing an eye is minimal. The main possible complications are infection (endophthalmitis), hemorrhage (expulsive hemorrhage, hemophthalmus) and dystrophy (epithelial-endothelial corneal dystrophy).

Even in the absence of complications when installing a phakic IOL, its lens often becomes cloudy over time (the phakic IOL touches the capsule of the natural lens, and chronic microtraumatization leads to cataracts).

With a complete replacement of the lens, the ability to accommodate disappears, that is, the patient sees well either in the distance or near. The solution is to implant multifocal IOLs with multiple foci, so that the brain itself chooses the focus that suits the moment. But every time it is impossible to accurately calculate the optical power of the IOL and set it perfectly. Often, after such operations, a small "plus", "minus" or astigmatism remains, not to mention higher-order aberrations. Reoperation dramatically increases the risk of complications, and an accurate refractive hit cannot be guaranteed a second time. Therefore, recently, with significant errors in the optical power after IOL implantation, LASIK has been performed. This combination was called bioptics.

Bioptics ("bi", "optics") - a change in two optical media - the cornea and the lens. Bioptic surgery now includes various combinations of operations: PRK + phakic IOL implantation, tangential keratotomy + cataract phacoemulsification, LASIK + clear lens aspiration with multifocal IOL implantation. Many different operations in various combinations.

Many methods have been proposed for LASIK + aspiration of the transparent lens (or phacoemulsification of cataract). For example, it was proposed to first form a corneal flap, after a few days to aspirate the lens with IOL implantation, and then a month later to do laser ablation to remove residual astigmatism. This approach reduces the risk of displacing the IOL during laser correction (namely, during the application of a vacuum ring) and at the same time removing not only congenital, but also residual (resulting from inaccurate IOL strength selection, etc.) astigmatism. However, if the IOL does not “dangle” within 3–6 months after implantation (there are no refractive and aberrometric vibrations), then it is impossible to move it with a vacuum ring. Therefore, performing LASIK six months after IOL implantation is also justified and safe.

Conducting a bioptical operation or only aspiration of a transparent lens during surgical correction of high myopia has one unpleasant nuance. The high risk of retinal detachment in an eye with severe myopia after abdominal surgery increases many times over, even despite preventive laser coagulation of the retina. If there are contraindications to laser correction and the risk of complications during abdominal operations, then you can continue to use glasses or contact lenses. However, in addition to abdominal surgeries, there is another alternative to LASIK.

Intracorneal (intracorneal) lenses and rings

Instead of implanting a lens inside the eye with a thin cornea, you can install it in the thickness of the cornea. Strictly speaking, the same LASIK, but after the formation of the corneal flap, it is not necessary to do laser ablation, but simply put a special microlens under the flap. ( In fact, it is not a flap that is cut out, but a special pocket in the thickness of the cornea. The operation is exaggerated for ease of understanding.) This is with hyperopia. When correcting myopia, it is impossible to put a negative lens instead of a positive one. The corneal flap covering her eliminates all her negativity.

Therefore, when correcting myopia, a lens is not implanted, but a ring is inserted along the periphery of the cornea. The corneal periphery raised by the ring transforms the anterior surface from a convex, positive lens to a negative one.

The disadvantages of this method are not very high accuracy of the refractive effect and the impossibility of eliminating astigmatism and higher-order aberrations. But in terms of safety, it is almost as good as LASIK. In the latest scientific works of foreign authors, a femtosecond laser is used to form a corneal tunnel for intracorneal rings. Such studies give hope that over time this method will become a real competitor to LASIK in the correction of myopia and hyperopia in patients with a thin cornea.

Excursion to ophthalmic implantology

Based on materials from the website of the Moscow State Institute of Radio Engineering, Electronics and Automation www.fcyb.mirea.ru (Implants in ophthalmology. Babushkina N.A.)

Ophthalmic implants are mainly used for the following purposes.

1. To correct violations in refractive diseases (myopia, hyperopia, presbyopia, astigmatism). Phakic refractive lenses, clear lens replacement, intracorneal implants and scleral implants.

2. For the surgical treatment of cataracts. Various types of intraocular lenses for lens replacement.

3. Retinal lesions (retinitis pigmentosa, macular degeneration, tapetoretinal abiotrophy, severe retinal lesions in complicated high-grade myopia, etc.). Electrical stimulation techniques.

Implantation in refractive surgery.

The first attempts to correct refractive errors were made over 200 years ago. These procedures, carried out by Tadini (1790) and Casannatta (1790), were aimed at reshaping the lens and reducing the anteroposterior size of the eye. After 100 years, V. Fukala showed that removal of the clear lens in high myopia leads to a positive result. But the spread of this refractive surgery was hampered by frequent complications - purulent infection and retinal detachment. According to the majority of those studying the history of this issue, it is the keratotomy for astigmatism, performed in 1885 by the Norwegian ophthalmologist L. Schiotz, that is the first refractive operation.

All implants for correcting eye refraction can be divided into the following groups.

Phakic lenses (PRL, Phakic Refractive Lens) - are installed parallel to the living lens.

IOL that replaces the living lens.

Scleral implants (SEBs, Scleral Expansion Bands).

Intracorneal rings (ICR, Intra Corneal Ring).

Today there are about 1500 IOL models manufactured by more than 30 companies around the world.

In the treatment of presbyopia, two technologies are leading - additional scleral segments, or scleral implants (SEBs, Scleral Expansion Bands) and phakic presbyopic IOLs.

Intracorneal rings (see above). The principal difference of this operation, as conceived by the authors, is the reversibility of the method. The implant can be removed if vision correction is required or there is a dissatisfaction with the corneal rings.

Telescopic IOLs. There is a retinal disease - age-related macular degeneration (AMD), which leads to loss of central vision and distortion of the geometry of the perceived image, as well as complete loss of vision. To correct the image, use special telescopic glasses, magnifiers and video enlargers of texts.

Figure: eighteen.

Some models of intraocular lenses (IOLs) and various haptic shapes

- haptic (attachment), - optical part (lens). A- anterior chamber phakic lens; B, C, G- lenses for replacing the crystalline lens (placed in the lens capsule); B, D, E- posterior chamber phakic lenses; F- lens for attaching to the iris.

Using accommodating IOLs. The frontal optical part of the Synchrony IOL, which has a greater optical power, is capable of three-dimensional movement - more intense in the anteroposterior direction, and less - at an angle tangential to the optical axis of the eye. Axial movement is the basis for refractive changes, but tangential movement of the front lens can change the refractive gradient of the optics, which increases the depth of focus and improves near vision.

IOL perspectives. In the future, the number of different IOL models will only increase. Already, there are lenses with a chromophore substance acting as a yellow filter. This is necessary to protect the retina from harmful ultraviolet radiation, which in a healthy eye partially retains the living lens. Also, microsensors are introduced into the IOL to monitor intraocular pressure. But the main efforts will be focused on eliminating the main disadvantages of the IOL: glair effect, optical aberrations, loss of accommodation and the appearance of glowing halos around bright light sources. Optical aberrations are proportional to lens thickness, so future IOLs will be very thin.

Medennium recently invented the Smart Lens. This IOL is able to change its shape at body temperature from a solid rod to a spherical gel-like accommodating lens that completely fills the capsular bag. At the moment, this device is the closest in properties to the natural lens. They can be custom made using MRI data on the exact size of the capsular bag and implanted through an incision as small as 1.0 mm.

In the future, it will also be possible to simulate the optical power of the lens in the postoperative period.

Thanks to overly optimistic media coverage, the greatest number of myths surround the work of scientists on the development of electrical implants. This is not surprising. Today, electrical implants are the most promising avenue for the treatment of irreversible blindness. Damage to the retina and optic nerve is now viewed as a sentence - humanity has not yet learned how to restore such a number of dead nerve cells. And the development of electrical implants offers hope for overcoming blindness.

Today, there are about 15 groups of scientists around the world engaged in the practical research and development of artificial retinas.

The scheme of operation of electric implants of an artificial retina is as follows.

A photo detector converts the light into an electrical signal. A transducer (microprocessor) converts the received electrical signal into a sequence of impulses that can be perceived by neurons. The electrodes, having received a signal from the transducer, stimulate neurons, thereby causing action potentials and further transmission of information to the nerve centers.

By placement, photodetectors are distinguished:

internal (a matrix of photodetectors installed on the fundus);

external (camera installed in special glasses).

Physically, the converter is a microprocessor, so it must be powered. There is not enough light energy to power the transducer and electrodes, so there must be an external renewable energy source. Such a source is located outside the human body and is powered by batteries. The transmission of energy is carried out wirelessly on the basis of electromagnetic induction: for this, a transmitting coil is placed on the "ears" of special glasses, and a receiving coil is implanted into the sclera of the eye, connected to microcircuits and electrodes. This does not apply to the ArtificalSilicon Retina (ASR) technology, where there is no transducer at all, and the stimulation by the electrodes is produced by light energy. Artifical Silicon Retina is a silicon chip with a diameter of 2 mm and a thickness of 25 microns, on which 5000 electrodes are placed. A photodiode is connected to each electrode, which converts light into electrical impulses, which are then transmitted to the cells of the retina. The chip is powered only by light energy and does not require external power sources. Preclinical tests have shown the presence of electroretinogram (ERG) signals and sometimes visual evoked potentials (VEPs) in the brain.

By the location of the electrodes, there are:

epiretinal technology (EPI-RET). In epiretinal technology, electrodes are placed over the retina and stimulate its ganglion cells;

subretinal technology (SUB-RET). Subretinal technology involves placing electrodes between the pigment layer and retinal receptors;

placement of implants at the optic nerve. A group of scientists in the framework of the European project MIVIP (Microsystems Based Visual Prosthesis) is studying the stimulation of the optic nerve directly by electrodes. The prosthesis includes an external chamber, a neurostimulator in a titanium case with spiral electrodes in the form of a cuff, and an interface for transmitting information and energy via radio waves. The electrode is implanted behind the eyeball in a free space where the optic nerve is not covered with a meninges, which would weaken the stimulation;

placement of implants in the visual areas of the cerebral cortex. Research on the introduction of artificial vision systems into the visual cortex of the cerebral hemispheres has been conducted since the 1960s. The entire prosthesis system is an external camera, a transducer, a set of electrodes and an interface for transmitting information and energy wirelessly. The neurostimulator is a matrix of needle electrodes made of biocompatible materials: Si or IrOx. Silicon is preferable, since microprocessor elements can be embedded in it. The brain is a viscoelastic material, so the insertion of the electrodes must be very fast (1 m / s). Otherwise, vascular damage and deformation of the cortical surface occur. Electrodes are placed in the primary visual cortex (zone V1, or 17th field according to Brodmann).

Ophthalmology does not stand still. New solutions appear every year. The development of chemistry, electronics and computer technology today makes it possible to use high-quality implants to eliminate the consequences of various eye diseases. Despite the psychological barrier that a person must cross to consent to the implantation surgery, as well as numerous possible complications, for many people implantation is the only chance to restore vision and improve their quality of life.