Electrophysiological examination of the eyes (EFI). Electrophysiological methods of research of Ethi view

17.06.2020

Clinical electrophysiology of the visual systemexamines electrical activity The main departments of the visual analyzer.

Electrophysiological methods allow you to objectively evaluate The functional state of the visual analyzer at the level of different layers and neurons of the retina and the visual path and used to diagnose various retinal and visual path diseases.

Features of electrophysiological methods:

Objective assessment of the functional state of the retina and the visual path
The possibility of early diagnosis at the subclinical level of a number of retinal diseases and spectator nerve and the visual path in general, including hereditary, as well as in some cases, identify carriers of pathological genes. This is especially important if there are no fairly pronounced ophthalmoscopic changes and violations of visual functions.
Differential diagnosis of retinal diseases and optic nerve.
Objective control in dynamics over the course of the disease and the effectiveness of the treatment.
The possibility is fairly accurately characterized by the functional state of the retina and the optic nerve in the clouds of transparent eyes, which is the prognostic criterion before different surgical interventions on the eyeball.
The ability to estimate the functional state of the organ of vision in children early agewhen subjective studies ineffective.

The main electrophysiological methods of the study of the body of the vision in the clinic are electroretinography (erg), electrocoooography (EOG) and the record of visual caused potentials of the cerebral cortex (ZVKP).

ERG is used to assess the functional state of the retina, the EOG - to evaluate the function of the pigment epithelium, ZVKP - to assess the visual path from the touch retina to the visual centers.

Methods complement each other, and their choice is determined by the need differential diagnosis and clarify the localization of the pathological process.

It is often necessary to use all EF research methods to assess the entire visual path.

Contraindications for electrophysiological research are the restless behavior of patients, epilepsy, and conjunctivitis, inflammatory diseases of the cornea and sclera, are added here to register Erg. early deadlines after operational treatment on the eye apple and the apparent eye.

Electricaloretinography (ERG)

ERG is a graphical mapping of changes in the bioelectric activity of the retinal cell elements in response to light irritation and is used to estimate the functional state of the retina.

Indications for electroretinography:

1. The need to evaluate the functional state of the retina, including in cases where it is impossible to determine the visual functions in the usual method, and the eye bottom is not ophthalmoscopy, when closering the media (belly of the cornea, cataract, hemophthalm), including for the prediction of visual functions in A result of the intended surgical treatment.

2. Diagnosis and differential diagnosis of retinal diseases, including hereditary, as in some cases, the ERG changes are pathognomonic symptoms of the disease. Diagnostics of the lesion of sticky and columm retinal systems. Amblyopia.

3. Evaluation of the depth, prevalence, localization and degree of retinal lesion (including during retinal detachment, diabetic retinopathy, injury, horooiditis, etc.).

4. Differential diagnosis of retinal diseases and visual nerve of various genes.

5. Detection of initial functional changes in the retina preceding clinical manifestations Diseases (medication intoxication, metal, sympathetic ophthalmia, vascular disorders, etc.).

6. Control over the dynamics of the pathological process and the effectiveness of treatment, the definition of the forecast.

7. Monitoring patients receiving drugs with a possible side retinotoxic effect with prolonged use.

8. Unexpected loss of vision.

9. Pediatric practice.

At the heart of adopted in electricoreography erg classification There are amplitude characteristics of the main A- and B-Waves of ERG, as well as their temporary parameters. The following types of erg are distinguished: normal, supernormal, subnormal (plus and minus-negative), outset, or unregistered (missing). Thus, in the pathological conditions of the retina, it is possible both a change in individual components of ERG and its complete disappearance.

Types of erg.

Maximum or mixed answer ( general or Ganzfeld Erg), consisting of a combination of components of sticky and colummer systems, reflects the function of the entire retina. Although under these conditions, the participation of the columns is large enough, dominates the answer of the rod system. The damage to the macular region with the localization of the pathological process within up to 6-15 ° does not affect the value of the general erg.
Rating of a stick system - scotopic (chopstick) erg.
Assessment of the Colummer System - photopic (colummer) erg and flashing (rhythmic) erg per frequency of the stimulus of 30 Hz. On the colummer (photopic) erg, registered on the presentation of single light stimuli or frequent flickers, affect the pathological processes, both those localized in the central retinal sections, and exciting periphery, where kolkochki also have. Thus, it is not purely macular, namely, the colummer answer. But the preferential contribution to this answer is made by precisely precisely the columns of the macular region due to their greatest numbers in this retinal zone.
Pattern Erg. it is a retina response to structured stimuli with permanent illumination (reversible chess or lattice patterns). PERG is used to diagnose macula dysfunction and diseases accompanied by a violation of the function of the ganglion cells of the retina (glaucoma).

Electrojulographyallows you to identify pathological changes in the retina and photoreceptors' pigment epithelium. To register a normal electroculogram, the normal functioning of photoreceptor and pigment epithelium, contact between these layers, as well as adequate choroidal blood supply is necessary.

For clinical purposes, the estimated value is used - the Arden coefficient.

Arden coefficient (ka) consider normalif it exceeds 185%. (Usually 180-250%). In order to assess the pathological states of the retina, they are divided into subnormal (135-185%), abnormal (110-135%), furious (100-110%), perverted (below 100%).

Electrojulography is used in the diagnosis of various diseases of the retina of dystrophic, inflammatory and toxic nature, with circulatory disorders and other pathology when pigment epithelium is involved in the process (Retinal pigment abiotrophy, congenital stationary night blindness, inference disease dr.).

Summary caused potentials (ZVP) allow us to estimate the functional state visual ways all over to central Departments visual analyzer.

The registration method of the SVP is used in the clinic for the diagnosis of pathology of the optic nerve and retrochiamatic lesions of the visual tract and visual centers; Under the edema of the optic nerve, inflammation, atrophy, compression damage to traumatic and tumor genesis, metabolic or toxic optical neuropathy, to assess the function of the optic nerve and visual paths after orbital and intracranial surgery, for the diagnosis of amblyopia.

The SVP complement the results of electroretology and can be the only source of information about the visual system in cases where Erg cannot be registered for one or another reasons.

Types of ZVP Depend on the nature of the stimulus: ZVP on the outbreak of light is called a flare (suspension), on the pattern-stimulus - Pattern-ZVP (PZVP). A reversing chess pattern is more often used as stimulation. The response generated is the most stable, the least variable on the amplitude and latency of the peaks.

Visual VI are also investigated in response to a standard photostimulation ("Flash"). The answer to such stimulation is less stable than when stimulated by a reversible chess pattern, having changed in a population even normally, less specific to assess the central vision. However, the visual VI to the outbreak has one important advantage over a chess pattern - they do not require the cooperation of the patient, can be registered in patients who cannot register the PATTER-ZVP in connection with a very low urgency of view and lacking a removal of the gaze.

Criteria of violations of visual paths when evaluation of ZVP There are no response or significant amplitude reduction, peak latency lengthening, significant differences in amplitude and latency when stimulating the right and left eyes. In general, latency is a more stable indicator, the amplitude of the peaks is more variable than latency.

Changes in the PZVP can be associated with the pathology of the macular field of the retina, therefore the information content of the results is significantly increased by simultaneously registering the ZVP from ERG.

Thus, according to the results of electrophysiological studies (EFI), it is possible to distinguish the norm from pathology, determine the level of defeat, as well as confirm or clarify the clinical diagnosis. In some cases, the EF-Changes are pathognomonic symptoms of the disease. However, Ethi is not an independent diagnostic tool and the interpretation of the results of electrophysiological research methods should always be held in context clinical picture Diseases.

Electrophysiological examination of the eyes is a number of highly informative methods for the study of the functions of the optic nerve, the retina and the visual regions of the cortex of the brain. The method is based on the registration of eye reactions to specific incentives.

Indications for E epi eye

Ethi eye study is assigned in the presence of certain testimony. These include:

atrophy of the optic nerve or suspicion of it;
retina dystrophy or suspected of it in order to observe the dynamics;
opacity of optical media impedicing ophthalmoscopy;
congenital myopia (the method determines the level of defeat of visual analyzers, which increases the efficiency of further treatment and improve visual functions);
amblyopia of any degree (EFI eyes in this case helps to resolve the issue of the need for further treatment and further expanded diagnostics);
acquired myopia with spraying pigments in the field of retina or with complaints with twilight vision;
suspected demyelinizing diseases of the nervous system or their presence.

In addition, EHFA has proven itself as one of the most effective and informative in the case of pathological clans (hypoxia, presence and hypotrophy of the fetus), congenital developmental anomalies and strabismus monolateral (one-sided). The method objectively evaluates visual functions in children under 3, when testing of visual acuity is difficult on objective reasons.

Electrophysiological examination of the eyes is not carried out by persons with the pathological activity of the nervous system (attacks, epilepsy).

Procedure varieties

There are 4 types of ehi eyes.

Electro-building. This method allows you to register changes in the constant potential of the cornea-retinal area of \u200b\u200bthe eye, while driving to the parties. The EOG depends on the degree of preservation of the pigment epithelium. Changes in an electroculogram indicate the presence of diseases that are localized in the membrane of the Bruchi, the choriocapillary retinal layer, as well as in the pigment epithelium.

Electricaloretinography. The method allows you to obtain a graphic image of the retinal electrical activity, which occurs in response to irritation with light. Erg shows the activity of most retinal cells, which depends on the number of healthy neurons and photoreceptors. Each cell layer is displayed on an electric sinogram separately as a curve of the graph. Assessing the cell reaction to certain incentives, the doctor determines how these cell groups function.

Method multifocal electroreoreography. The MEGR building builds a three-dimensional card showing the photosensitivity of the most important field of retina in terms of functionality - central. In addition, the method reveals small foci of lesion in this field of retina.

Spectally caused potentials. EVP is the reaction of the visual nerves of the crust in the occipital region of the brain on the light irritation of the eyes (17 - 19 of the field of the bark according to Brodman). The above potentials are recorded as a electroencephalogram, which demonstrates the functional state of the departments of visual analyzers. That is why EFI Eye Study by the EVP method plays an important role in the topical diagnosis of developing pathology. Flares or structured incentives (alternation of ferrous and white cells of different variables) can act as an incentive, which depends on the visual acuity of the examined and objectives of the study.

An ophthalmologist and a researcher who applies eye examination of the eye, work in close contact among themselves to put the task and decide on the view of the survey and choose the early or differential diagnosis. Electrophysiologist selects a study plan to get an answer from those retina cells that are involved in pathological processes. Ethi eye give objective results, being determining when formulating diagnosis.

Cost

The price of E epi eye will depend on the selected procedure. For example, electricoretinography costs about 3150 rubles, and electroculography is about 2650 rubles. The cost of studying visual caused potentials ranges from 2500 to 4000 rubles.

Electrophysiological study (EFI) Eyes are a number of highly informative methods for studying the function of the optic nerve, a mesh shell, visual regions in the cerebral cortex. The study is carried out by registering the reactions of the visual analyzer to emerging specific incentives.

Indications for EFI

Indication for Effi Eye, is the diagnosis of the following diseases:

Atrophy of the optic nerve and suspicion of it;
Retinal degeneration and suspected of it to observe the dynamics;
Congenital myopia to determine the degree of lesion of the visual analyzer;
Opacity of optical media complicating ophthalmoscopy;
Amblyopia of any extent to address the issue of expanded diagnosis and further treatment;
Acquired myopia when spraying pigments in the field of the mesh shell and the weakening of twilight vision;
Demyelinizing pathology of the nervous system and suspicion of them.

In addition, Ehi eye is one of the most effective information in terms of pathological childbirth (hypoxia, prematurity, fetal hypotrophy), congenital anomalies development and monolateral seproinacy (one-sided). The method makes it possible to objectively evaluate the visual functions of children under 3 years old, whose checking of visual acuity is predica to objective reasons.
This study Not appointed to persons having nervous diseases (For example, epilepsy).

Video of our research specialist

Procedure varieties

Ethi eye, includes 4 types of research:

Electrojulography (EOG) is a method that allows you to register the variability of constant potential in the cornea-retinal region during the movement of the eyes to the parties. The purpose of the EOG depends on the preservation of the pigment epithelium. Possible changes in the electroculogram, as a rule, indicate the presence of pathology localized in the membrane of the Bruch, pigment epithelium or the choriocapillary retinal layer.

Electricaloretinography (erg) is a method that makes it possible to obtain graphic images of retinal electrical activity arising in response to light irritation. It shows the activity of the objective majority of retinal cells - healthy photoreceptors and neurons. Each cell of the cells on the electroretrogram is displayed as a separate curve of the graph. In assessing the cell reaction to certain incentives, the specialist determines the possible functions of these cellular groups.

Multifocal electroretinography (MEARG) - a method that allows you to build a three-dimensional card of indicators of photosensitivity most important in the functional plan of the retinal area - central. At the same time, the method allows you to identify small foci of damage to this area.

The method of visually induced potentials (ZVP) is the reaction of the visual nerves of the occipital region of the cerebral cortex on the emerging light irritation of the eyes (according to Brodman 17-19 fields of the crust). The above potentials are recorded as an electroencephalogram, which shows the functional state of the visual analyzers of interest. Therefore, ehi eye using the EUP, is particularly important in the topical diagnosis of progressive pathology. Incentives, as a rule, protrude light outbreaks or structured elements (alternation of white and black cells of different quantities), which is due to the tasks of the study and acuteness of the patient.

Ophthalmologist works closely with a specialist who performs an Effi eye examination, which makes it possible to determine the tasks, develop a survey plan, select an early or differential diagnosis. The electrophysiologist builds studies in such a way that the answers received from the retinal cells involved in pathological processes become determining when diagnosing formulation.

In the Moscow Medical Center Eye clinic"Everyone can undergo a survey on the most modern diagnostic equipment, and according to the results - to obtain a consultation of a high-class specialist. The clinic is open seven days a week and works daily from 9 h to 21 hours. Our specialists will help identify the reason for reducing vision, and will be competent treatment of identified pathologies.

15-08-2011, 09:12

Description

Electrophysiological research methods include:

* electroculography (EOG);

* Visual caused cortical potentials (or (ZVP)).

ERG- Graphic expression of bioelectric activity arising in response to the light stimulation of the retina. The current source is neuronal activity in the field of cell membranes, changing their polarity on depolarization or hyperpolarization. Erg consists of two main A- and B-waves reflecting the total bioelectric activity of all retinal cell elements (Fig. 20-1).

In the generation of bioelectric activity, the retina take part: photoreceptors, pigment epithelium, bipolar, horizontal, amacrin, interplexing and ganglion cells, as well as Muller cells. Network diseases are due to various reasons leading to anatomical and physiological disorders, which in turn determines the impairment of visual functions and the presence of characteristic functional electrophysiological symptoms.

TO pathological processesobserved and retina include dystrophy and degeneration (genetically deterministic or secondary); Inflammation, edema, ischemia, necrosis, hemorrhage, the deposition of solid or soft exudates and lipids, retinosisis, retinal delay, fibrosis, proliferation, formation of neovascular membranes, hyperplasia and a pigment epithelium hypoplasia, tumors, angioid stripes, etc. Despite the diversity of the ophthalmoscopic disease The retina, pathophysiological manifestations can be similar to different nosological forms, and vice versa with similar changes in the eye bottom Pathophysiological mechanisms can be different. All these processes can be observed with ophthalmoscopy of the eye-eye bottom, and each of them can to some degreely change the bioelectric activity of the retina and have its electrorette symptoms. At the same time, the primary localization of pathological processes in the retina is different for different nosological forms: in the vessel layer of choroids, the membrane of Bruchi, pigment epithelium, photoreceptor-pigment epithelium complex, photoreceptors, inner layers of retina, ganglion cells and their axons. The origin of the ERG components in different layers of the retina and the connection of them with different neurons and retinal photoreceptors determine the specificity of electrophysiological symptoms, pathognomonicity of electroretteographic and electroculographic symptoms, which are often considered leading in the diagnosis and differential diagnosis of retinal diseases, pigment epithelium and choroids with different pathogenesis and localization.

EOOG.- The method registering the permanent potential of the eye, which reflects continuously flowing in the retina exchange processes And actively forms them. Under the influence of adequate stimuli in a healthy eye and in pathological processes in the retina, pigment epithelium and choroids, there are characteristic changes in the permanent potential of the eye (Fig. 20-2).

Reflecting functions different structures retina ERGand EOOG.complement to each other, representing a holistic picture of functional disorders of peripheral sections of the visual system.

Summary caused cortical potentials The total bioelectric activity of the cortical neurons of visual centers and other brain departments occurring to the flash of light or structured incentives, such as a chess reversing field. Graphically, they are represented by a certain set of positive and negative oscillations, the amount and magnitude of which depend on the study method and the incentive used. This method allows to investigate the functional state of the fields 17, 18, 19 visual bark in Brodmann. The visual caused cortical potentials generates predominantly the striarior bark, their response to the pattern-stimulus reflects the activity of the bark induced by the afferent impulses coming along the retinogenicular paths. The visual caused cortical potentials occur in the 4C layer of the striar cortex of the VI zone - projections of a macular region, sensitive to changes in brightness, contour boundaries, contrast and spatial frequency of the chess field elements, as well as in the extrastrace regions (Fig. 20-3).

The study of the functional state of various parts of the visual system from choroids, pigment epithelium, sensory retina to visual centers.

The study of the function of various channels of the visual system, the functions of photoreceptor, sticky and columine paths (scotopic and photopic systems).

Allocation of the function of photoreceptors, hyperpolarizing and depolarizing bipolar, Muller cells, amacrine and ganglion cells in the norm and pathology, peripheral and central retinal departments.

ZVPs are used to assess the functional state of the visual ways, the visual nerve, chiazas and posthiasmal departments, as well as visual centers. ZVP reflects mainly the electrical activity of the macular area. The time of excitation from the retina in a visual nerve to the visual centers is used to estimate the functional state of ganglion cells and axons forming the visual nerve.

Indications

Indications for the use of ERG, EOG and visual caused cortical potentials Combined in one rubric, since each of these methods makes its information in the process of diagnosing and studying the visual system, enriching the information obtained by specific characteristics. At the same time, to clarify the localization of the origin of the pathological process in the retina and visual nerve, as well as the diagnosis, you can use all three methods in one patient.

Study of pathophysiological mechanisms of violation of visual functions.
Confirmation of the diagnosis with known electrophysiological symptoms, the diagnosis of hereditary diseases of the retina and syndromic lesions, identification of pathological generators, eye hypertension and glaucoma, siderosis, retinal detachment, multiple sclerosis, inflammatory eye diseases, sympathetic ophthalmia, endophthalmite, retina ischemia with diseases such as other vehicles and arteries of retina, etc.
Differential diagnosis of retinal diseases of various origins.
Control over the dynamics of the pathological process and the effectiveness of treatment.
Monitoring patients with general systemic diseases of the body having an eye as a target organ for possible complications, as well as patients, long-term receiving drugs with possible by-effect on the organ of view, such as chlorookhin, hydroxychlorookhin, ethambutol, phenothiazine, adeogol, toluen, deferoxamine, tamoxifen, etc.
Unexpected loss of vision, including psychiatric violations.
Luling optical media (crystal, cornea, st).
Pediatric Neurophthalmological Practice:

* Premature birth of a child, delay in the development of visual functions, violation of the removal of the gaze, oculotor disorders:
* Assessment of the function of the visual analyzer in the absence of vision or changes in the eye dna. with reduced vision in relatives or with their hereditary diseases diagnosed in them;
* Monitoring the development of a visual system, no binocular vision. amblyopia, albinism;
* Monitoring visual functions in the first year of life, obtaining indicative information about visual acute (using Pattern-ZVP).

Study of the retinal function and optic nerve during injury, monitoring in the presence of metallic foreign bodies in the eye.
Diagnostics of diseases of the optic nerve (its edema, inflammation, atrophy, compression damage to traumatic and tumor genesis) and conducting visual tracts and centers (cysts, malformations, etc.): Assessment of the function of the optic nerve in the process of orbital and intracranial surgery (with the help of visual circulators potentials).
Uveta, as the depression of ERG and EOG may indicate the need to intensify treatment.
Thyareotoxicosis, endocrine of office, since the depression of visual caused cortical potentials and the change in ERG may indicate the compression of the optic nerve and retinal ischemia.
Vascular diseases accompanied by retinal ischemia (DR, Retinopathy at arterial hypertension and etc.).

Contraindications

Diseases of the cornea, conjunctivations, early time after surgical treatment (for ERG), restless behavior of patients, tendency to epileptic supplies.

Preparation

Patient preparation includes adaptation to the dark or light, the imposition of active and reference electrodes, respectively, standard (on the eye, cornea, conjunctival cavity, scalp, etc.), dosing of the load on the organ of view (relaxation position, fixation of the light source, minimization of morganation and movement Eye) and explanation that the study is carried out. If necessary, spend optical correction, expansion of pupil.

Methodology and subsequent care

Electrodeoretianography

Several ways of registration of ERGs are used, allowing to highlight a columine (photopic) and a sticky (scotopic) retina system, the function of photoretors and various retinal neurons. For their allocation, appropriate conditions for adaptation and stimulation are used in which each of these systems dominates.

a) mixed (maximum) response in a dark adapted eye,
b) a simple colummer answer;
c) a stick response in a dark adapted eye;
d) oscillatory biopotentials;
e) Flyer response, occurs with a quickly repeated incentive with a frequency of 30 Hz (flashing or rhythmic ERG).

Macular, multifocal, pattern-erg, erg for a long-term stimulus of different intensity and colors are used additionally when localizing the pathological process in retinal structures and solving diagnostic problems. The macular erg characterizes the function of the macular region, the multifocal erg - the topography of its bioelectric activity, the components of the pattern-erg - the function of the macular region and ganglion cells of the retina, and the ERG to the long-term stimulus - on- and off-response of the colummer and on-stick visual tract.

Mixed (maximum) The response in a dark adapted eye (Fig. 20-5), consisting of a combination of replies of sticky and colummer systems, is recorded with a uniform stimulation of the entire retina with a standard stimulus of 1,5-4.5 kD / m2 with a duration of 5 ms with an interval between stimuli 10 with With an extended pupil after 3-5 minutes of dark adaptation.

Simple colummer (photopic)the answer (Fig. 20-6) is recorded on a standard stimulus with an interval of 0.5 s in photopic conditions on a background of 17-34 cd / m in a square (5-10 FL), overwhelming rolling activity, after 10 minutes of preliminary luminous adaptation.

Rush answer (Fig. 20-7)- The first signal after the completion of the dark adaptation is at least 20 minutes, since the sticks are very sensitive to the light and deadaption occurs immediately after lighting. The scotopic response is recorded on an incentive weaker than a standard 2.5 log. Unit with an interval between stimuli 2 p.

Oscillatory biopotentials - Small oscillations (Fig. 20-8) on the ascending part of the B-wave, the generation of which is determined by the activity of the amacrine cells, the relationship of neurons in the inner layers of the retina, the colummer and the rod. The oscillatory biopotentials from the dark adapted eye immediately after turning off the light when using a standard white stimulus for maximum erg, with an interval between stimuli 15 with or from a light adapted eye with an interdimular interval of 1.5 s. The number of oscillatory biopotentials is normal from 4 to 7, with pathology, their configuration changes, the oscillation amplitude decreases, their latency is lengthened.

Flashing (Flycher) Ergregistered with a standard white stimulus with a frequency of 30 Hz in photopic conditions reflects the function of the colummer system (Fig. 20-9). For light adaptation, overwhelming rolling activity, use background 17-34 kD / m2 (5-10 FL).

Pattern Erg (Fig. 20-10) - The response of the central field of retina on the isolumnant stimulus, a black and white chess reversing field. Pattern Erg, reflecting the mainly activity of the ganglion cells of the retina and the functional state of the macular region, is generated by the internal layers of the retina.

Pattern Erg is recorded on a reversive chess pattern with maximum contrast, the value of the stimulation field is 10-20, the size of chess squares is 15-60 minutes, with the brightness of the stimulus (display) 80 kD / m2, reverse frequency - 2-6 reversions per second (1- 3 Hz), the bandwidth of the amplifier 1-100 Hz. The ERG pattern consists of the first negative component of N35, not having a clinical value, and two main components: positive - about 50 ms (P50) and a large negative - about 95 ms (N95). The value of Pattern Erg is very small, so a large number of averages are needed for its registration. The component of P50 pattern-ERG depends on the normal functioning of the macular region. The selective absence of N95 is noted for diseases of the optic nerve (Fig. 20-11).

ERG on incentives of big duration Registered in photopic conditions on a bright stimulus 200-500 ms on a background of up to 35 kD / m in a square in order to suppress the function of the sticky apparatus. Reflects the activity of on-bipolar cells (depolarized) and OFF-bipolar cells (hyperpolarized), which may independently change with the diseases of the retina of different genes (Fig. 20-12).

Local macular erg. They register from the central, macular area of \u200b\u200bthe retina to the red, green and blue incentives of small angular sizes (15 °) in photopic conditions when using the averaging method, which allows you to allocate the dominant function of the colummer system (Fig. 20-13).

Control fixation of the eye Possible in different ways. When using the source of local light stimulation (LED) installed directly on the electrode suction cup with an inserted optical system, which, together with an optical eye system, creates a fixed image of the light source on the central field of the retina, there is no need to additionally control the labeling of the gaze (Fig. 20-14) .

Multifocal Erg. - The method of registration of local bioelectric responses in the central field of retina. The method allows to analyze the topography of bioelectric activity of the retinal field of the visual field and study nonlinear responses associated with adaptive mechanisms of visual tract, isolate bioelectric responses of the outer and internal retinal layers. The stimulation of the central retinal area (60 °) is carried out in stimuli of the hexagonal shape, which has a pseudo-rapidly virtual number of times with a frequency in each stimulated point of 16 Hz (electrical monitor with a frequency of 75 Hz) flashing with a binary M-sequence. The stimulus increases from the center to the periphery, respectively, the size of the retinal recipe fields. The response localization corresponds to each hexagonal element, and the ERG topography is presented on the computer display (Fig. 20-15).

The mathematical model represents the topography of the bioelectric activity of the macular region (the density of the distribution of bioelectric activity) in the three-dimensional image (Fig. 20-16).

Electrojulography

Reducing the reference of the retina, the transition to the complete darkness causes a permanent potential drop to the lowest level (the level of "dark depressions"). Light in the eye, adapted to the dark, causes a large rise in constant potential, called "light peak" and caused by depolarization of the apical part of the pigment epithelium cells, the amplitude of which, at certain limits, is proportional to the retinal light log logarithm. The luminous rise and the dark drop is recorded in various conditions of adaptation - light (50-100 kD / m2) and dark (each each), since with dosage horizontal movements of the eyes every 1-2 with within 30 °, the voltage change between the front And the rear poles of the eye. The alternative method uses 40 min. Dark adaptation with subsequent registration of the EOG during bright light. Considate the ratio of the light peak to the baseline obtained after 40 minutes of dark adaptation. Registration is carried out using skin electrodes recorded from the inner and outer cantus of both eyes with an earthen electrode on the forehead surface.

To implement normal light-month fluctuations in constant potential, the necessary conditions are considered the normal functioning of photoreceptor and pigment epithelium, contact between these layers, as well as normal choroidal blood supply.

Summary caused potentials

Types of ZVP depend on the incentive. ZVP on the outbreak of light 20 ° optic angle with a duration of 5 ms and the brightness of 3 cd / m in the square is distinguished by greater variability. They are usually registered with low visual sharpness. The SVP on the pattern-incentive is called Pattern ZVP (Fig. 20-17).

When registering the pattern, the incentives are presented either in switching on-shutdown mode, when the average illumination of the pattern and the replacing it is constant, either in the reversion mode 1-4 cycle per second, when and permanently present on the monitor screen of the chess field. White squares are replaced by black , and black - white. The study is carried out without mydriasis. When registering the Pattern ZVP, a correction of vision studied in advance is required, to the distance to the incentive. Usually use monocular stimulation, which is sometimes impossible to carry out young children (then a binocular study is carried out).

Special conditions for visual stimulation, registration and analysis of the ZVP make it possible to use them to localize the level of defeat of the visual path. To such conditions, in particular, the stimulation of certain sections of the field of view (half-haters, quadrants, local stimulation) and a comparative analysis of the components of the ZVP in lateral occipital leads, which makes it possible to assess the participation of each hemisphere in the generation of ZVP.