B scan. Varieties of ultrasound eye diagnostics

Ultrasound of the eye- a method for diagnosing ophthalmic diseases, visualizing the structure of the eye, the state of the optic nerves, muscles and blood vessels, lens, retina. Used within comprehensive diagnostics myopia, hyperopia, astigmatism, retinal dystrophy, cataracts, glaucoma, eye tumors, trauma, vascular pathologies, neuritis. Several variants of the procedure are widespread: one-dimensional (A), two-dimensional (B), three-dimensional (AB) scanning, USDG / USDS of vessels. The cost depends on the selected ultrasound mode.

Training

Ultrasound of the eye does not require advance preparation. Immediately before the procedure, it is necessary to remove makeup from the eyes, remove contact lenses... If you suspect the presence of a foreign body in the eye tissues up to ultrasound examination an x-ray of the eye is taken. With the development of a neoplasm of any etiology, preliminary diaphanoscopy or X-ray examination is recommended.

What shows

The result of ultrasound of the eye in the A-scan mode is a one-dimensional image, the obtained parameters are used to calculate the strength of the intraocular lens before the operation of cataract removal. In B-mode, a two-dimensional image of the sockets and eyeballs is obtained, the study reveals corneal opacities, cataracts, hemorrhages, foreign bodies, neoplasms in the eye. In complex AB mode, the structures of the eye are displayed in a three-dimensional image. The study of blood vessels reflects the characteristics of blood flow in real time through graphical and quantitative indicators. The following pathologies can be detected by ultrasound of the eye:

• Myopia, hyperopia. The length of the anteroposterior axis of the eyeball is measured. With congenital myopia, it over normal, with farsightedness - less.
• Cataract. Normally, this structure is transparent and does not appear on the monitor. When clouded, the lens becomes denser and begins to reflect ultrasound waves - it becomes visible.
• Degenerative-dystrophic diseases. Retinal degeneration, optic nerve atrophy, glaucoma, keratopathy, conjunctival dystrophy are accompanied by thinning and death of cells. On ultrasound images, the affected areas become less bright - from white and light gray to gray, barely detectable.
• Neoplasms, foreign body. The study allows you to determine the size and location of the tumor, foreign object eyes. On ultrasound, they look like areas of increased and high echo activity.
• Pathology of the optic nerves. Assessment of the state of the visual nerve fibers necessary for retrobulbar neuritis, neurogenic tumors, glaucoma, traumatic lesions... The change in the thickness of the sheath and disc of the nerve, the expansion of certain parts of it, and the blurring of the boundaries are determined.
• Vascular pathology of the eye. Ultrasound of the eye vessels is used to analyze blood flow in case of age-related, diabetic, atherosclerotic changes. The study reveals thrombosis of small and large vessels, non-perfused microvessels, vascular malformations, narrowing of the lumen, scarcity of branching, slowing blood flow, twisting and undulating course of vessels.

In addition to the above, an ultrasound of the eye is prescribed to identify congenital anomalies development of the organ of vision, diseases of the lacrimal glands and lacrimal sac. Despite the high information content, the ultrasound results cannot be the only confirmation of the diagnosis. They are used in combination with the data of a clinical survey, anamnesis, ophthalmological examination, radiography and other instrumental methods.

Advantages

Currently, eye ultrasound is the most informative and accessible method. early diagnosis ophthalmic pathologies. The advantages of the method include harmlessness: the absence of radiation exposure and invasive intervention allows examining children, the elderly, pregnant women, and nursing mothers. The short duration of the examination procedure and the relatively low cost make ultrasound one of the most common methods of screening for eye diseases. The disadvantage of ultrasound examination of the eye - the clarity of the image is limited by the area of ​​the sensor, the resolution is lower than with MRI and CT.

The medical terms "A-scan of the eye" and "echobiometry" are used to denote a diagnostic method aimed at measuring the depth of the anterior ophthalmic chamber, the length of the eyeball and the thickness of the lens. These measurements have not only diagnostic value in determining myopia and other disorders, but also, along with data on the parameters of the curvature of the cornea, make it possible to determine the strength of the IOL before surgery.

You can complete the procedure at the Sfera ophthalmological clinic. We carry out comprehensive studies using modern equipment that allow us to obtain accurate information, thanks to which the results of any treatment will be better.

What is it - eye echobiometry?

A-scan of the eye is a one-dimensional ultrasound scan, during which all data is displayed on the monitor in the form of a corresponding graph. Diagnostics can be carried out using ultrasound equipment or optical method.

Indications and contraindications for A-scan

How is an A-scan of an eye done?

A-scan (ultrasound of the eye) involves the use of anesthetic drops. Immediately before the procedure, the doctor instills them into the patient's eye in order to eliminate discomfort, blinking and tearing. The patient assumes a sitting or lying position. The doctor places the sensor on the surface of the open eye and moves it smoothly. The data obtained during the scanning process goes to the computer and is displayed on the monitor.

Interpretation of A-scan results

By comparing the results obtained with normal parameters, the ophthalmologist can determine the patient's myopia or hyperopia. For example, the normal length of the eye axis is 23 mm. If the patient has myopia, they exceed them, hyperopia, on the contrary, decreases. Based on the data obtained, the patient can choose glasses or contact lenses, determine the tactics of treatment or plan an operation.

Benefits of A-scan in our clinic

The Sfera clinic has been providing its services to everyone who wants to see well for more than 20 years and is a recognized leader in its field. We have at our disposal a powerful diagnostic base, which includes an installation for performing echobiometry. This is an ultrasound scanner "A-Scan Plas", created at the production facilities of the company "Accutome" (USA). It can be used to scan any type of eye, including the presence of mature cataract... IOL calculations carried out by "A-Scan Plas" allow achieving maximum accuracy: up to 0.25D.

To get an appointment with our specialists, use the online form on our website or call us: +7 495 139-09-81.

Ultrasound diagnostics is an effective method of examination in case of violations of the transparency of the optical media of the eye. It is advisable that the procedure is performed by the operating surgeon, and not by the doctor or nurse from the diagnostic department. In this way, the patient's condition is determined more accurately and the optimal treatment tactics are selected.

To obtain accurate diagnostic results, it is necessary to correctly understand the principles of the effect of ultrasonic flows on body tissues.

In ophthalmology, reflected ultrasonic echo pulses are used. Short pulses have a frequency of 10 MHz or higher. The sensor stably records the reflected signals at a pulse repetition rate of 1-5 kHz. The average velocity of propagation of ultrasonic energy in the tissues of the eye is 1540 m / s. Allows you to calculate and display on the monitor the distance between the transducer and the echo reflecting fabric. Reflecting, the ultrasonic pulse is refracted at the interface between media of different densities.

With a small radius of curvature of the piezoelectric transducer, an inaccurate image is formed at the focal point. Beams of ultrasound pulses of 3 mm at a level of 6 dB give insufficient quality lateral resolution. Pictures that are at close range are doubled on the monitor. Pictures far from the sensor appear blurry in the lateral areas.

Frequency and axial resolution are related. Increasing the frequency increases the clarity of the resolution. If a wide beam of pulses returns from curved surfaces, the axial resolution is reduced.

Since the higher frequencies are better captured by the body, additional power is needed for weak impulses. The maximum power that can be used depends on the presence of cataracts.

Clinical practice has shown that a high-quality result can be obtained by generating a 10-20 MHz signal and an axial resolution of about 0.15 mm. The perpendicular hit of ultrasonic waves on the surface provides the best signal reflection. The monitor does not show all cross-sections even if the correct pulse amplitude is selected.

Since sound travels faster through the lens, structures located behind the lens look closer on the monitor than in reality, and at the edge of the lens, the wave is refracted.

The most acoustically dense structures - intraocular foreign bodies, lens, intraocular lenses are characterized by many internal reflections. They are shown on the monitor as evenly spaced signals with decreasing amplitude behind the main signal. They can be recognized thanks to the paradoxical movements when sliding the device.

It happens that retrolental membranes are impregnated with calcium salts. Pronounced shadows appear on the monitor. calcified structures absorb some of the impulses.

With repeated passage of ultrasound pulses through tissues, the display shows distant structures with a reduced amplitude. This absorption can be compensated for by amplifying the signal from distant structures.

Devices that display the surfaces of the sclera, retina, and cornea on a screen can produce diagnostically inaccurate readings. For example, it is possible to mistake CT for the retina. Also, electronic recognition rejects impulses with a minimum amplitude inside the CT, subretinal fluid, lens, etc.

A-scan

One of the types of ultrasound is A-scan or amplitude ultrasonography. Does not play a significant role in the diagnosis of opaque optical media of the eye. Returns a flat bitmap (ID) that is difficult to navigate. An inexperienced physician will offer an ambiguous interpretation. And only an ophthalmologist with extensive experience can give an informative result. The amplitude of the echo signal in this type of examination strongly depends on the angle of reflection of the pulse from the ocular structures. The indirect angle greatly attenuates the reflected signal, fragments with strong and weak echoes will appear from the folds of the retina. Therefore, A-scan is considered to be a method that gives a lot of errors.

B-scan

With sectoral ultrasound (synonymous with B-scan), sections or planes of tissues are scanned. The result is presented as an array of pixels, ranked by intensity.

As in the previous method, strong signals are reflected by structures located perpendicular to the ultrasonic pulses. The retina, sclera, lens capsules and cornea are clearly displayed.

3D eye modeling

By rotating the scanning sector slowly, you can obtain volumetric images in the form of cones. They can be shown on the monitor as 3D using perspective, shadow, parallax, etc. Since the model is built when the waves diverge from one point, the surfaces of structures that are not localized perpendicularly will be skipped or shown with a lower echo amplitude. So far, 3D ultrasound machines are rarely used.

Ultrasound diagnostics significantly improves examination of patients with opaque optical media of the eye. It's best if given view the research is performed by the surgeon who will operate on the patient, and not by the specialist of the diagnostic department. During the study, the surgeon can fully assess the patient's condition, which allows him to optimize the choice of tactics for his treatment. If the ultrasound equipment is installed in the surgeon's office, it is used much more often and does not require unnecessary investment of time to get ready for work. Unlike ophthalmoscopy, ultrasound should not be trusted by nurses.

Understanding physical principles the interaction of ultrasonic energy and body tissues is necessary to conduct accurate. In ophthalmology, a reflected ultrasonic echo pulse is used. Short ultrasonic pulses have a frequency of 10 MHz or more, the center pulse repetition rate is 1-5 kHz, which allows the transducer to record the reflected echo signal. Knowledge average speed the propagation of ultrasonic energy in tissues (~ 1540 m / s) makes it possible to calculate in real time and display on a flat display the distance between the transducer and the reflecting echo structure in a two-dimensional projection (2D). The ultrasonic wave is reflected and refracted at the interface between media of different acoustic density.

If the surface piezoelectric crystal sensor has a small radius of curvature, the depth of field of the spatial image at the focal point will be insufficient. The long eye (25mm) requires more uniform focusing to obtain an appropriate depth of field. A wide beam of ultrasonic waves (3 mm at a level of 6 dB) is characterized by insufficiently high lateral resolution. The images of targets located at a close distance appear double on the display, and those located far from the sensor appear blurred in the lateral areas. Such errors are inevitable if computer sonography is not used, but it is currently not available for performing ultrasound in ophthalmology.

Axial permission depends on the frequency, at a higher frequency it is higher. Higher frequencies are more readily absorbed by biological structures, so more power is needed to provide sensitivity to weak echoes. The risk of developing cataracts determines the maximum power that can be used safely. In practice, experts have come to a compromise that ultrasound with a frequency of 10-20 MHz and an axial resolution of about 0.15 mm should be used, which is an order of magnitude higher than the lateral resolution. Axial resolution is reduced if a wide wave beam is reflected off curved surfaces such as those seen in TOC.

Better ultrasonic signal reflection is achieved when a beam of ultrasonic waves hits the surface perpendicularly. Waves reflected from the wall of the orbit in the equator of the eye give a weak reflected signal. Even with the correct echo amplitude, not all circular cross-sections of the eye can be reflected on the display.

Because speed sound higher in denser structures such as the lens, the structures behind it are projected closer to the display than they actually are, and wave refraction occurs along the edge of the lens. The lens, IOL, IOIT and scleral fillings, characterized by high acoustic density, give multiple internal reflections, displayed on the display in the form of evenly distributed false echoes with reduced amplitude behind the main echoes of these structures. Echoes are produced by paradoxical movements as the transducer is moved to aid in their recognition. Dense structures such as calcified retrolental membranes, IOLs, and IOLs create significant shadows behind them due to the absorption of acoustic energy.

Absorption of ultrasonic energy when it travels twice through tissues, it displays distant structures with relatively lower echo amplitudes. Electronic amplification of echoes from distant targets can compensate for this absorption. This technique is called gain over time.

Usage electronic devices that automatically display the surface of structures such as the cornea, lens capsule, retina and sclera, leads to diagnostic errors. Increasing the amplitude and clipping the peaks to display the surface of the structures on the display means that all echoes are displayed at identical amplitudes. With this approach, the CT and the retina in the image can be easily confused. In addition, electronic differentiation in determining the surface of structures eliminates echo signals with the smallest amplitude inside the lens, CT, subretinal fluid (SRF), suprachoroidal space, and tumors.

A-scan... Amplitude ultrasonography (A-scan) is an original ultrasound method, but has no significant practical value in the presence of opaque optical media of the eye. An A-scan produces a flat one-dimensional image (ID), and it is as difficult to find the information you need as a needle in a haystack. A very experienced diagnostician can spatially integrate a 1D image and gain some benefit from the data obtained. The less experienced diagnostician, however, has much more problems when interpreting its results. The informative value of a quantitative A-scan for diagnostics is much less than is commonly believed. The amplitude of the A-scan echo is largely dependent on the angle at which the ultrasonic waves are reflected from the structures of the eye being examined. An indirect angle causes significant attenuation of the reflected signal.

Folds detached retina will create areas of strong and weak echoes. For this reason, A-scan is characterized by a large error in the results.

B-scan... A sectoral ultrasound, or B-scan, is a two-dimensional (2D) scan that scans sections, or planes, of tissue, as opposed to an ID point A-scan. The echo image appears on the display as intensity modulated pixels. As with the A-scan, a stronger signal is reflected by structures located strictly perpendicular to the direction of the ultrasonic waves. For this reason, the cornea, anterior and posterior lens capsules, sclera or retina are best displayed on the display. The equatorial part of the sclera and the nucleus of the lens are less visible, unless the position of the eyeball is changed or the sensor is not installed at different angles. It is possible to assess whether such actions are necessary during the research.

3D visualization of the eyes... Slow rotation of the scanning sector allows obtaining volumetric conical images that can be displayed on the display as conical 3D images or 3D slices using perspective, shadows, parallax (the visible change in the position of an object when the observer moves) and various other digital graphic technologies. Since the images are formed when the beam of ultrasonic waves is emitted from a single point, structures with surfaces located not perpendicular to the scanning beam will be indistinguishable or they will have a lower echo amplitude. Modern 3D ultrasound devices are of minimal importance in the diagnosis of vitreoretinal pathology, they are best used to determine the volume of the tumor.

In many areas of medicine, ultrasound scanning is actively used as a highly informative method of diagnosis that has practically no contraindications. In ophthalmology, it is also used to help accurately diagnose pathological processes in the eyes. Examination of the organ of vision in A-scan mode is also known as eye echobiometry.

Method essence

The A-scan is an example of a one-dimensional scan. During it, the following is measured:

• the depth of the eye chamber (exclusively anterior);
• lens thickness;
• the length of the eye - this indicator helps to clearly establish the degree of myopia.

The received information is reflected on the monitor in the form of a graph with two axes - vertical and horizontal. The obtained indicators of eye echobiometry are used to analyze all structures of the eye, which makes it possible to obtain a complex picture.

Echobiometry lasts an average of 15 minutes to half an hour. The eyes should be open throughout this time. The procedure does not require the use of painkillers, therefore it is recommended for both adults and children.

Ultrasound of the organ of vision: indications, contraindications

Echobiometry of the eye in children is carried out when the indicators obtained during the study with a slit lamp are not very informative.

Indications for ultrasound in children are the following conditions:

• suspected arterial thrombosis;
• neoplasms;
• foreign bodies in the eye;
• hypertension, which can lead to retinal detachment;
• congenital anomalies.

Echobiometry of the eye in adults has the same indications for conducting.

At the same time, such an absolutely safe study as echobiometry, in the case of prescriptions in children, has certain contraindications:

• open trauma to the organ of vision;
• violation of the integrity of the eyelid and the area around the eyes;
• bleeding.

The listed contraindications are also relevant for adult patients.

What the results show

Echobiometry is a rather informative research method. It should be remembered that only a specialist will be able to establish what indicators are the norm. A table is often used to decipher the results.

The norm for children is almost the same as for adults. In general, to calculate the indicators, special formulas are used, which give an accurate answer to the question of what is the norm of eye echobiometry in patients of a given age.

Research technique

Echobiometry is performed in a sitting position or, in extreme cases, lying down (this position is recommended for children and the elderly). To immobilize eyeball, the doctor instills special drops. The sensor in the case of echobiometry touches directly the organ of vision.

Today, the method is sufficiently developed and allows for a fairly accurate study of the eye, its internal structure.

The specialist on the monitor observes all the data that characterize the cornea:

• thickness;
• the degree of transparency;
• structure, integrity.

Comparing the average statistical data and the results obtained, the doctor determines which indicators are normal and which deviate.

Conducting an ultrasound examination of the organ of vision allows you to avoid many pathological processes or to detect them at an early stage.