Chronic pyelonephritis national recommendations. Clinical guidelines for pyelonephritis. Chronic pyelonephritis in men

Analyzers perform a large number of functions or operations on signals. The most important among them are: I. Signal detection. II. Signal discrimination. III. Signal transmission and conversion. IV. Coding of incoming information. V. Detection of certain signs of signals. VI. Pattern recognition. As with any classification, this division is somewhat arbitrary.

Detection and discrimination of signals (I, II) is provided primarily by receptors, and detection and identification of (V, VI) signals by higher cortical levels of analyzers. Meanwhile, transmission, conversion and coding of (III, IV) signals are characteristic of all layers of analyzers.

I,Signal detection begins in receptors - specialized cells, evolutionarily adapted to perceive a particular stimulus from the external or internal environment of the body and transform it from a physical or chemical form into a form of nervous excitation.

Classification of receptors. All receptors are divided into two large groups: external, or exteroceptors, and internal, or interoceptors. Exteroceptors include: auditory, visual, olfactory, taste, tactile receptors; interoreceptors include visceroreceptors (signaling the state of internal organs), vestibulo- and proprioceptors (receptors of the musculoskeletal system).

Based on the nature of contact with the environment, receptors are divided into distant ones, which receive information at some distance from the source of stimulation (visual, auditory and olfactory), and contact receptors, which are excited by direct contact with it.

Depending on the nature of the stimulus to which they are optimally tuned, human receptors can be divided into 1) mechanoreceptors, k. which include auditory, gravitational, vestibular, tactile skin receptors, musculoskeletal receptors, and baroreceptors of the cardiovascular system; 2) chemoreceptors, including taste and olfactory receptors, vascular and tissue receptors; 3) photoreceptors, 4) thermoreceptors(skin and internal organs, as well as central thermosensitive neurons); 5) painful(nociceptive) receptors, in addition to which pain stimuli can be perceived by other receptors.

All receptor apparatuses are divided into primary sensers(primary) and secondary senses(secondary). The first include olfactory receptors, tactile receptors and proprioceptors. They differ in that the perception and transformation of the energy of irritation into the energy of nervous excitation occurs in their most sensitive neuron. Secondary sensory receptors include taste, vision, hearing, and vestibular receptors. Between the stimulus and the first sensitive neuron there is a highly specialized receptor cell, i.e. the first neuron is not excited directly, but through a receptor (not nerve) cell.

According to their basic properties, receptors are also divided into quickly and slowly adapting, low and high threshold, monomodal and polymodal, etc.

In practical terms, the most important is the psychophysiological classification of receptors according to the nature of the sensations that arise when they are irritated. According to this classification, humans have visual, auditory, olfactory, taste, tactile receptors, thermoreceptors, receptors for the position of the body and its parts in space (proprio- and vestibuloreceptors) and pain receptors.

Mechanisms of receptor excitation. When a stimulus acts on a receptor cell, changes occur in the spatial configuration of protein receptor molecules embedded in the protein-lipid complexes of its membrane. This leads to a change in the permeability of the membrane for certain ions (most often sodium) and the appearance of an ionic current, generating the so-called receptor potential. In primary sensory receptors, this potential acts on the most sensitive areas of the membrane, capable of generating action potentials - nerve impulses.

In secondary sensory receptors, the receptor potential causes the release of transmitter quanta from the presynaptic ending of the receptor cell. A mediator (for example, acetylcholine), acting on the postsynaptic membrane of a sensitive neuron, causes its depolarization (postsynaptic potential - PSP). The postsynaptic potential of the first sensory neuron is called generator potential and it leads to the generation of an impulse response. In primary sensory receptors, the receptor and generator potentials, which have the properties of a local response, are one and the same.

Most receptors have so-called background impulses (spontaneously release a transmitter) in the absence of any stimulation. This allows you to transmit information about the signal not only in the form of an increase in frequency, but also in the form of a decrease in the flow of pulses. At the same time, the presence of such discharges leads to the detection of signals against the background of “noise”. “Noise” refers to impulses not associated with external stimulation that arise in receptors and neurons as a result of the spontaneous release of transmitter quanta, as well as multiple excitatory interactions between neurons.

This “noise” makes signals difficult to detect, especially when their intensity is low or changes are small. In this regard, the concept of response threshold becomes statistical: it is usually necessary to determine the threshold stimulus several times in order to make a reliable decision about its presence or absence. This is true both at the level of behavior of an individual neuron or receptor and at the level of the reaction of the entire organism.

In an analyzer system, the procedure of multiple evaluations of a signal to make a decision about its presence or absence is replaced by a comparison of simultaneous reactions to this signal of a number of elements. The issue is resolved as if by voting: if the number of elements simultaneously excited by a given stimulus is greater than a certain critical value, it is considered that the signal has occurred. It follows that the threshold of the analyzer system’s response to a stimulus depends not only on the excitation of an individual element (be it a receptor or a neuron), but also on the distribution of excitation in the population of elements.

The sensitivity of receptor elements to so-called adequate stimuli, to the perception of which they are evolutionarily adapted (light for photoreceptors, sound for receptors of the cochlea of ​​the inner ear, etc.), is extremely high. Thus, olfactory receptors are able to be excited by the action of single molecules of odorous substances, photoreceptors are able to be excited by a single quantum of light in the visible part of the spectrum, and the hair cells of the spiral (corti) organ respond to displacements of the basilar membrane of the order of 1 10"" M (0.1 A°) , i.e. for vibration energy equal to 1 ^0~ ^ " G V^/cm 2 (^ 10~ 9 erg/(s-cm 2). A higher sensitivity in the latter case is also impossible, since the ear would then hear the thermal (Brownian) motion of molecules in the form of constant noise.

It is clear that the sensitivity of the analyzer as a whole cannot be higher than the sensitivity of the most excitable of its receptors. However, in addition to receptors, sensitive neurons of each nerve layer, which differ in excitability, participate in signal detection. These differences are very large: for example, visual neurons in different parts of the analyzer differ in light sensitivity by 10 7 times. Therefore, the sensitivity of the visual analyzer as a whole also depends on the fact that at increasingly higher levels of the system the proportion of highly sensitive neurons increases. This helps the system reliably detect weak light signals.

I. Signal discrimination. So far we have been talking about the absolute sensitivity of analyzers. An important characteristic of how they analyze signals is their ability to detect changes in intensity, timing, or spatial features of a stimulus. These analyzer system operations related To;";: a number of signals begin already in the receptors, but the following analyzer signals also participate in it. It is necessary to ensure a different reaction to the minimum |!«;!„!!|chie between stimuli. This minimal difference is the threshold of discrimination (di-!;o1:!;s;"(threshold, if we are talking about comparing intensities).

In 1834, E. Weber formulated the following law: the perceived increase in irritation (threshold of discrimination) must exceed the irritation that acted previously by a certain proportion. Thus, an increase in the sensation of pressure on the skin of the hand occurred only when an additional load was applied, constituting a certain part of the load placed earlier: if previously there was a weight weighing 100 g, then it was necessary to add 3-10~ (for the person to feel this addition). 2 (3 g), and if the weight was 200 g, then the barely noticeable addition was 6 g. The resulting dependence is expressed by the formula: D///===const1, where / is irritation. A/ is its perceived increase (discrimination threshold), const! is a constant value (constant).

Similar relationships were obtained for vision, hearing and other human senses. Weber's law can be explained by the fact that when the intensity level of the main long-acting stimulus increases, not only the response to it increases, but also the “noise of the system”, and also the adaptive inhibition deepens. Therefore, in order to again achieve reliable discrimination of additives to this stimulus, they must be increased until they exceed the fluctuations of these increased noises and exceed the level of inhibition.

A formula has been derived that expresses in a different way the dependence of sensation on the strength of stimulation: E==a-1o^1-(-b, Where E - the magnitude of the sensation, / is the strength of stimulation, and and and are constants that are different for different signals. According to this formula, sensation increases in proportion to the logarithm of the intensity of stimulation. This general expression, called Weber's law- Fechner, confirmed in many different studies.

Spatial discrimination of signals is based on differences in the spatial distribution of excitation in the receptor layer and in the nerve layers. So, if any two stimuli excite two neighboring receptors, then distinguishing between these two stimuli is impossible, but they will be perceived as a single whole. To spatially distinguish two stimuli, it is necessary that there be at least one unexcited receptor element between the receptors they excite. Similar effects occur during the perception of auditory stimuli.

To temporarily distinguish between two stimuli, it is necessary that the neural processes caused by them do not merge in time and that the signal caused by the subsequent stimulus does not fall into the refractory period from the previous stimulus.

In the psychophysiology of the sense organs, the threshold value of a stimulus is taken as the probability of perception of which is 0.75 (the correct answer about the presence of a stimulus in 3/4 of the cases of its action). It is natural that lower intensity values ​​are considered subthreshold, and higher ones are considered suprathreshold. However, it turned out that even in the “subthreshold” range a clear, differentiated reaction to ultra-weak (or ultra-short) stimuli is possible. Thus, if the light intensity is reduced so much that the subject himself can no longer say whether he saw the flash or not, then based on the objectively recorded skin-thalvanic reaction, it is possible to identify a clear response of the body to this signal. It turns out that the perception of such ultra-weak stimuli occurs at a subthreshold level.

111. Transfer and transformation. After the energy of a physical or chemical stimulus is converted in the receptors into the process of nervous excitation, a chain of processes begins to transform and transmit the received signal. Their goal is to convey to the higher parts of the brain the most important information about the stimulus and, moreover, in a form most convenient for its reliable and rapid analysis.

Signal transformations can be conditionally divided into spatial and temporal. Among the spatial transformations of signals, one can single out a change in their scale as a whole or a distortion in the ratio of different spatial parts. Thus, in the visual and somatosensory systems at the cortical level, there is a significant distortion of the geometric proportions of the representation of individual parts of the body or parts of the visual field. In the visual cortex, the representation of the central fovea of ​​the retina is sharply expanded with a relative reduction in the periphery of the visual field (“cyclopean eye”).

Temporal transformations of information are reduced mainly to its compression into separate pulses, separated by pauses or intervals. In general, the transition from tonic impulses of neurons to phasic burst discharges of neurons is typical for all analyzers.

The total electrical response of the retina to light is called an electroretinogram (ERG). It can be recorded from the whole eye or directly from the retina. To do this, one electrode is placed on the surface of the cornea, and the other on the skin of the face near the eye or on the earlobe. On the electroretinogram, several characteristic waves are distinguished (Fig. 14.8). Wave A reflects the excitation of the internal segments of photoreceptors (late receptor potential) and horizontal cells. Wave b arises as a result of activation of glial (Müller) cells of the retina by potassium ions released during excitation of bipolar and amacrine neurons. Wave With reflects the activation of pigment epithelial cells, and the wave d - horizontal cells.

The ERG clearly reflects the intensity, color, size and duration of action of the light stimulus. The amplitude of all ERG waves increases in proportion to the logarithm of the light intensity and the time during which the eye was in the dark. Wave d (response to switching off) is greater the longer the light is on. Since the ERG reflects the activity of almost all retinal cells (except ganglion cells), this indicator is widely used in the clinic of eye diseases for diagnosis and treatment monitoring for various retinal diseases.

Excitation of retinal ganglion cells leads to impulses being sent along their axons (optic nerve fibers) to the brain. The retinal ganglion cell is the first neuron of the “classical” type in the photoreceptor-brain circuit. Three main types of ganglion cells have been described: those that respond to light being turned on (on-response), to light being turned off (off-response), and to both (on-off-response) (Fig. 14.9).

The diameter of the receptive fields of ganglion cells in the center of the retina is much smaller than in the periphery. These receptive fields are circular in shape and concentrically constructed: a round excitatory center and a circular inhibitory peripheral zone, or vice versa. As the size of the light spot flashing in the center of the receptive field increases, the response of the ganglion cell increases (spatial summation). Simultaneous excitation of closely located ganglion cells leads to their mutual inhibition: the responses of each cell become smaller than with a single stimulation. This effect is based on lateral, or lateral, inhibition. The receptive fields of neighboring ganglion cells partially overlap, so that the same receptors can be involved in generating the responses of several neurons. Due to their circular shape, the receptive fields of the retinal ganglion cells produce a so-called point-by-point description of the retinal image: it is displayed as a very fine mosaic consisting of excited neurons

^ Electrical phenomena in the subcortical visual center and visual cortex. The pattern of excitation in the neural layers of the subcortical visual center - the external or lateral geniculate body (NCT), where the fibers of the optic nerve arrive, is in many ways similar to that observed in the retina. The receptive fields of these neurons are also round, but smaller than those in the retina. The neuronal responses generated in response to a flash of light are shorter here than in the retina. At the level of the external geniculate bodies, the interaction of afferent signals coming from the retina occurs with efferent signals from the visual area of ​​the cortex, as well as through the reticular formation from the auditory and other sensory systems. These interactions ensure the selection of the most essential components of the sensory signal and the processes of selective visual attention.

The impulse discharges of the neurons of the lateral geniculate body travel along their axons to the occipital part of the cerebral hemispheres, where the primary projection area of ​​the visual cortex (striate cortex, or field 17) is located. Here, much more specialized and complex information processing occurs than in the retina and the external geniculate bodies. Neurons of the visual cortex have not round, but elongated (horizontally, vertically, or in one of the oblique directions) receptive fields of small size. Thanks to this, they are able to select from a whole image individual fragments of lines with one or another orientation and location (orientation detectors) and selectively respond to them.

The brain receives more than 90% of sensory information through the organ of vision. From the entire spectrum of electromagnetic radiation, the photoreceptors of the retina register only waves with a length from 400 to 800 nm. The physiological role of the eye as an organ of vision is twofold. First, it is an optical instrument that collects light from environmental objects and projects their images onto the retina. Second, photoreceptors in the retina convert optical images into neural signals that are transmitted to the visual cortex.

Organ of vision(Figure 10-1) includes eyeball, connected through the optic nerve to the brain, protective apparatus(including eyelids and lacrimal glands) and motion apparatus(striated oculomotor muscles). Eyeball. The wall of the eyeball is formed by membranes: in the anterior part there are conjunctiva And cornea, in the back - retina, choroid And sclera. The cavity of the eyeball occupies vitreous body. Anterior to the vitreous body is a biconvex lens Between the cornea and the lens there are

Fig.10-1. Eyeball.Inset: pupillary reflex

aqueous humor front camera(between the posterior surface of the cornea and the iris with the pupil) and rear camera eyes (between the iris and lens).

Protective apparatus of the eye. Long eyelashes the upper eyelid protects the eye from dust; The blink reflex (blinking) occurs automatically. Eyelids contain meibomian glands, thanks to which the edges of the eyelids are always moisturized. Conjunctiva- thin mucous membrane - lines both the inner surface of the eyelids and the outer surface of the eyeball. Lacrimal gland secretes tear fluid that irrigates the conjunctiva.

Retina

A diagram of the visual part of the retina is shown in Fig. 10-2. At the posterior edge of the optical axis of the eye, the retina has a rounded yellow spot about 2 mm in diameter (Fig. 10-2, inset). Fossa fovea- the depression in the middle part of the macula is the place of best perception. Optic nerve exits the retina medial to the macula. Here it is formed optic disc (blind spot), not perceiving light. In the center of the disk there is a depression in which the vessels supplying the retina are visible. In the visual retina, starting from the outermost - pigment (prevents the reflection and scattering of light passing through the entire thickness of the retina, see arrow in Fig. 10-2) and to the innermost - layer of nerve fibers (axons of ganglion neurons) of the optic nerve, the following are distinguished: layers.

External nuclear The layer contains the nucleated parts of photoreceptor cells - cones and rods. Cones concentrated in the macula area. The eyeball is organized in such a way that the central part of the light spot from the visualized object falls on the cones. Along the periphery of the macula are located sticks.

Outer mesh. Here contacts are made between the internal segments of rods and cones with the dendrites of bipolar cells.

Internal nuclear. Here are located bipolar cells, connecting rods and cones with ganglion cells, as well as horizontal and amacrine cells.

Inner mesh. In it, bipolar cells contact ganglion cells, and amacrine cells act as interneurons.

Ganglion layer contains cell bodies of ganglion neurons.

Rice. 10-2. Retina(B - bipolar cells; D - ganglion cells; mountains - horizontal cells; A - amacrine cells). Inset- ocular fundus

The general scheme of information transmission in the retina is as follows: receptor cell, bipolar cell, ganglion cell, and at the same time, amacrine cell - ganglion cell, axons of ganglion cells. The optic nerve exits the eye in an area visible through an ophthalmoscope as optic disc(Figure 10-2, inset). Photoreceptor cells(Fig. 10-3 and 10-5B) - rods and cones. The peripheral processes of photoreceptor cells consist of outer and inner segments connected by a cilium.

Outer segment has many flattened closed disks (duplicates of cell membranes) containing visual pigments: rhodopsin(absorption maximum - 505 nm) - in sticks: red(570 nm), green(535 nm) and blue(445 nm) pigments - in cones. The outer segment of rods and cones consists of regular membrane formations - disks(Figure 10-3, right). Each photoreceptor contains more than 1000 disks.

Internal segment filled with mitochondria and contains a basal body, from which 9 pairs of microtubules extend into the outer segment.

Central vision and visual acuity realized by cones.

Peripheral vision, and night vision And perception of moving objects- functions of sticks.

OPTICS OF THE EYE

The eye has a system of lenses with different curvatures and different refractive indices of light rays (Fig. 10-4.1), including

Fig.10-3. Retinal photoreceptors.The outer segments are enclosed in a rectangle

There are four refractive media between: O air and the anterior surface of the cornea; About the posterior surface of the cornea and the aqueous humor of the anterior chamber; About the aqueous humor of the anterior chamber and the lens; About the posterior surface of the lens and the vitreous body.

Refractive power. For practical calculations of the refractive power of the eye, the concept of the so-called “reduced eye” is used, when all refractive surfaces are algebraically added and considered as one lens. In such a reduced eye with a single refractive surface, the central point of which is located 17 mm anterior to the retina, the total refractive power is 59 diopters when the lens is adapted for viewing distant objects. The refractive power of any optical system is expressed in diopters (D): 1 diopter is equal to the refractive power of a lens with a focal length of 1 meter.

Accommodation- adaptation of the eye to clearly seeing objects located at different distances. The main role in the process of accommodation belongs to the lens, which can change its curvature. In young people, the refractive power of the lens can increase from 20 to 34 diopters. In this case, the lens changes shape from moderately convex to significantly convex. The mechanism of accommodation is illustrated in Fig. 10-4, II.

Fig.10-4. OPTICS OF THE EYE. I The eye as an optical system. II Accommodation mechanism. A is a distant object. B - nearby object. III Refraction. IV Visual fields. The broken line outlines the visual field of the left eye, the solid line outlines the visual field of the right eye. The light (heart-shaped) area in the center is the binocular vision zone. The colored areas on the left and right are monocular vision fields)

When looking at distant objects (A), the ciliary muscles relax, the suspensory ligament stretches and flattens the lens, giving it a disc-shaped shape. When looking at close objects (B), a more significant curvature of the lens is required for full focusing, so the SMCs of the ciliary body contract, the ligaments relax, and the lens, due to its elasticity, becomes more convex. Visual acuity- the accuracy with which the object is visible; theoretically, the object should be of such a size that it could stimulate one rod or cone. Both eyes work together (binocular vision) to transmit visual information to the visual centers of the cerebral cortex, where the visual image is evaluated in three dimensions.

Pupillary reflex. The pupil, a round hole in the iris, changes in size very quickly depending on the amount of light falling on the retina. The pupil lumen can vary from 1 mm to 8 mm. This gives the pupil the properties of a diaphragm. The retina is very sensitive to light (Figure 10-1, inset), and too much light (A) distorts colors and irritates the eye. By changing the lumen, the pupil regulates the amount of light entering the eye. Bright light causes an unconditional reflex autonomic reaction that closes in the midbrain: the sphincter of the pupil (1) in the iris of both eyes contracts, and the dilator of the pupil (2) relaxes, as a result the diameter of the pupil decreases. Poor lighting (B) causes both pupils to dilate so that enough light can reach the retina and excite the photoreceptors.

Friendly pupil reaction. In healthy people, the pupils of both eyes are the same size. Lighting one eye causes the pupil of the other eye to constrict. This reaction is called a friendly pupil reaction. In some diseases, the pupil sizes of both eyes are different (anisocoria).

Depth of focus. The pupil enhances the clarity of the image on the retina by increasing the depth of field. In bright light, the pupil has a diameter of 1.8 mm, in average daylight illumination - 2.4 mm, in the dark the pupil dilation is maximum - 7.5 mm. Pupil dilation in the dark degrades the quality of the retinal image. There is a logarithmic relationship between the pupil diameter and lighting intensity. The maximum increase in pupil diameter increases its area by 17 times. The light flux entering the retina increases by the same amount.

Focus control. Lens accommodation is regulated by a negative feedback mechanism, automatically adjusting the focal power of the lens for the highest visual acuity. When the eyes are fixed on a distant object and must immediately change their fixation to a near object, accommodation of the lens occurs within a fraction of a second, providing better visual acuity. If the point of fixation unexpectedly changes, the lens always changes its refractive power in the desired direction. In addition to the autonomic innervation of the iris (pupillary reflex), the following points are important for focusing control.

❖ Chromatic aberration. Red rays focus later than blue rays because the lens refracts blue rays

stronger than red ones. The eyes are able to determine which of these two types of rays is in better focus and send information to the accommodative mechanism with instructions to make the lens stronger or weaker.

❖ Spherical aberration. By transmitting only the central rays, the pupil eliminates spherical aberration.

❖ Convergence of the eyes when fixating on a close object. The neural mechanism that causes convergence simultaneously signals an increase in the refractive power of the lens.

❖ Degree of lens accommodation oscillates constantly but slightly twice per second, allowing the lens to respond more quickly to establish focus. The visual image becomes clearer when the oscillations of the lens enhance changes in the desired direction; clarity decreases when the power of the lens changes in the wrong direction.

❖ Areas of the cerebral cortex those that control accommodation interact with the neural structures that control the fixation of the eyes on a moving object. The final integration of visual signals occurs in Brodmann's areas 18 and 19, then motor signals are transmitted to the ciliary muscle through the brain stem and Edinger-Westphal nuclei.

❖ Point of closest vision- the ability to clearly see a nearby object in focus - becomes distant during life. At the age of ten, it is approximately 9-10 cm and moves away to 83 cm at the age of 60 years. This regression of the point of closest vision occurs as a result of decreased elasticity of the lens and loss of accommodation.

Presbyopia. As a person gets older, the lens grows, becomes thicker and less elastic. The ability of the lens to change its shape also decreases. The power of accommodation drops from 14 diopters in a child to less than 2 diopters in a person aged 45 to 50 years and to 0 at age 70 years. Thus, the lens loses its ability to accommodate, and this condition is called presbyopia (senile farsightedness). When a person reaches a state of presbyopia, each eye remains at a constant focal length; this distance depends on the physical characteristics of each individual's eyes. Therefore, older people are forced to use glasses with biconvex lenses.

Refractive errors. Emmetropia(normal vision, Fig. 10-4,III) corresponds to a normal eye if parallel rays from distant objects are focused on the retina when the ciliary

the muscle is completely relaxed. This means that the emmetropic eye can see all distant objects very clearly and easily transition (through accommodation) to clear vision of nearby objects.

❖ Hypermetropia(farsightedness) may be caused by an eyeball that is too short or, in more rare cases, by the fact that the eye has a lens that is too inelastic. In the farsighted eye, the longitudinal axis of the eye is shorter, and the beam from distant objects is focused behind the retina (Fig. 10-4, III). This lack of refraction is compensated by a farsighted person by accommodative effort. A farsighted person strains the accommodative muscle when looking at distant objects. Attempts to look at nearby objects cause excessive strain on accommodation. To work with close objects and read, farsighted people should use glasses with biconvex lenses.

❖ Myopia(myopia) represents the case when the ciliary muscle is completely relaxed, and light rays from a distant object are focused in front of the retina (Fig. 10-4,III). Myopia occurs either as a result of the eyeball being too long, or as a result of the high refractive power of the eye's lens. There is no mechanism by which the eye could reduce the refractive power of the lens when the ciliary muscle is completely relaxed. However, if an object is close to the eyes, a nearsighted person can use the mechanism of accommodation to focus the object clearly on the retina. Therefore, a nearsighted person is limited only to the clear point of “far vision.” For clear distance vision, a nearsighted person needs to use glasses with biconcave lenses.

❖ Astigmatism- unequal refraction of rays in different directions, caused by different curvature of the spherical surface of the cornea. Accommodation of the eye is unable to overcome astigmatism, because the curvature of the lens changes equally during accommodation. To compensate for deficiencies in corneal refraction, special cylindrical lenses are used.

Visual field and binocular vision

❖ Visual field each eye is part of the external space visible to the eye. In theory it should be round, but in reality it is cut medially by the nose and the upper edge of the eye socket! (Fig. 10-4,IV). Mapping

visual field is important for neurological and ophthalmological diagnostics. The circumference of the visual field is determined using the perimeter. One eye closes and the other fixates on the central point. By moving a small target along the meridians towards the center, the points are marked when the target becomes visible, thus describing the visual field. In Fig. 10-4,IV, the central visual fields are outlined along a tangent line with solid and dotted lines. White areas outside the lines are a blind spot (physiological scotoma).

❖ Binocular vision. The central part of the visual fields of the two eyes completely coincides; therefore, any area in this visual field is covered by binocular vision. Impulses coming from two retinas, excited by light rays from an object, merge into one image at the level of the visual cortex. The points on the retina of both eyes where the image must fall in order for it to be perceived binocularly as a single object are called corresponding points. Light pressure on one eye causes double vision due to misalignment of the retinas.

❖ Depth of vision. Binocular vision plays an important role in determining the depth of vision based on the relative sizes of objects, their reflections, and their movement relative to each other. In fact, depth perception is also a component of monocular vision, but binocular vision adds clarity and proportionality to depth perception.

FUNCTIONS OF THE RETINA

Photoreception

The discs of photoreceptor cells contain visual pigments, including rod rhodopsin. Rhodopsin (Fig. 10-5A) consists of a protein part (opsin) and a chromophore - 11-cis-retinal, which under the influence of photons turns into trance-retinal (photoisomerization). When light quanta hit the outer segments in photoreceptor cells, the following events occur sequentially (Fig. 10-5B): activation of rhodopsin as a result of photoisomerization - catalytic activation of G protein (G t, transducin) by rhodopsin - activation of phosphodiesterase upon binding to G t a - hydrolysis cGMP by cGMP phosphodiesterase - transition of cGMP-dependent Na+ channels from an open to a closed state - hyperpolarization of the plasma membrane of a photoreceptor cell - signal transmission to bipolar cells.

Rice. 10-5. RHODOPSIN AND ACTIVATION OF ION CHANNELS. A. Opsin molecule contains 7 transmembrane alpha-helical regions. The filled circles correspond to the localization of the most common molecular defects. Thus, in one of the mutations, glycine in the second transmembrane region at position 90 is replaced by asparagine, which leads to congenital night blindness. B. Transmembrane protein rhodopsin and its connection with G-protein (transducin) in the plasmalemma of the photoreceptor cell. Rhodopsin, excited by photons, activates the G protein. In this case, guanosine diphosphate bound to the α-CE of the G protein is replaced by GTP. The cleaved α-CE and β-CE act on phosphodiesterase and cause it to convert cGMP into guanosine monophosphate. This closes the Na+ channels, and Na+ ions cannot enter the cell, which leads to its hyperpolarization. R - rhodopsin; α, β and γ - G protein CE; A - agonist (in this case light quanta); E - phosphodiesterase effector enzyme. B. Diagram of a stick. In the outer segment there is a stack of discs containing the visual pigment rhodopsin. The disc membrane and the cell membrane are separated. Light (hv) activates rhodopsin (Rh*) in the discs, which closes the β+ channels in the cell membrane and reduces the entry of Na+ into the cell

Ionic basis of photoreceptor potentials

❖ In the dark Na The + channels of the membrane of the outer segments of rods and cones are open, and current flows from the cytoplasm of the inner segments into the membranes of the outer segments (Fig. 10-5B and 10-6,I). The current also flows into the synaptic terminal of the photoreceptor, causing a constant release of the neurotransmitter. Na+,K+-

Figure 10-6. ELECTRICAL REACTIONS OF THE RETINA. I. Photoreceptor response to illumination. II. Ganglion cell responses. Illuminated fields are shown in white. III. Local potentials of retinal cells. P - sticks; GC - horizontal cells; B - bipolar cells; AK - amacrine cells; G - ganglion cells

the pump located in the inner segment maintains ionic equilibrium by compensating the Na+ output with the K+ input. Thus, in the dark, ion channels are kept open and the flows into the cell of Na+ and Ca 2+ through open channels provide the appearance of current (dark current). ABOUT In the light those. when light excites the outer segment, the Na + channels close and a hyperpolarizing receptor potential. This potential, which appears on the membrane of the outer segment, extends to the synaptic ending of the photoreceptor and reduces the release of the synaptic transmitter - glutamate. This immediately leads to the appearance of APs in the axons of ganglion cells. This way

zom, hyperpolarization of the plasmalemma- a consequence of ion channel closure.

ABOUTReturn to original state. Light, which causes a cascade of reactions that lower the concentration of intracellular cGMP and leads to the closure of sodium channels, reduces the content of not only Na+, but also Ca2+ in the photoreceptor. As a result of a decrease in Ca 2 + concentration, the enzyme is activated guanylate cyclase, synthesizing cGMP, and the content of cGMP in the cell increases. This leads to inhibition of the functions of light-activated phosphodiesterase. Both of these processes - an increase in cGMP content and inhibition of phosphodiesterase activity - return the photoreceptor to its original state and open Na+ channels.

Light and dark adaptation

❖ Light adaptation. If a person is exposed to bright lighting for a long time, then a significant portion of the visual pigments are converted into retinal and opsin in the rods and cones. Most of the retinal is converted into vitamin A. All this leads to a corresponding decrease in the sensitivity of the eye, called light adaptation.

❖ Dark adaptation. On the contrary, if a person remains in the dark for a long time, then vitamin A is converted back into retinal, retinal and opsin form visual pigments. All this leads to increased sensitivity of the eye - dark adaptation.

Electrical responses of the retina

Various cells of the retina (photoreceptors, bipolar, horizontal, amacrine, as well as the dendritic zone of ganglion neurons) generate local potentials, but not PD (Fig. 10-6). Of all retinal cells PD arise only in the axons of ganglion cells. Total electrical potentials of the retina - electroretinogram(ERG). ERG is recorded as follows: one electrode is placed on the surface of the cornea, the other on the skin of the face. ERG has several waves associated with the excitation of various retinal structures and collectively reflects the intensity and duration of light exposure. ERG data can be used for diagnostic purposes in retinal diseases

Neurotransmitters. Retinal neurons synthesize acetylcholine, dopamine, Z-glutamic acid, glycine, γ-aminobutyric acid (GABA). Some neurons contain serotonin, its analogues (indolamines) and neuropeptides. Rods and cones in

synapses with bipolar cells secrete glutamate. Various amacrine cells secrete GABA, glycine, dopamine, acetylcholine and indoleamine, which have inhibitory effects. Neurotransmitters for bipolar and horizontal have not been identified.

Local potentials. The responses of rods, cones and horizontal cells are hyperpolarizing (Fig. 10-6, II), the responses of bipolar cells are either hyperpolarizing or depolarizing. Amacrine cells create depolarizing potentials.

Functional features of retinal cells

Visual images. The retina is involved in the formation of three visual images. First image formed under the influence of light at the level of photoreceptors, turns into second image at the level of bipolar cells, in ganglion neurons it is formed third image. Horizontal cells also take part in the formation of the second image, and amacrine cells are involved in the formation of the third.

Lateral inhibition- a way to enhance visual contrast. Lateral inhibition is the most important element of the activity of sensory systems, allowing the enhancement of contrast phenomena in the retina. In the retina, lateral inhibition is observed in all neural layers, but for horizontal cells it is their main function. Horizontal cells laterally synapse with the synaptic sites of rods and cones and with the dendrites of bipolar cells. A mediator is released at the ends of horizontal cells, which always has an inhibitory effect. Thus, lateral contacts of horizontal cells ensure the occurrence of lateral inhibition and the transmission of the correct visual pattern to the brain.

Receptive fields. In the retina, for every 100 million rods and 3 million cones, there are about 1.6 million ganglion cells. On average, 60 rods and 2 cones converge per ganglion cell. There are large differences between the peripheral and central retina in the number of rods and cones converging on ganglion neurons. At the periphery of the retina, photoreceptors associated with one ganglion cell form its receptive field. Overlapping the receptive fields of different ganglion cells allows for increased light sensitivity at low spatial resolution. As you approach the central fossa, the ratio of rods and

The cone ganglion cells become more organized, with only a few rods and cones per nerve fiber. In the area of ​​the fovea, only cones remain (about 35 thousand), and the number of optic nerve fibers emerging from this area is equal to the number of cones. This creates a high degree of visual acuity compared to the relatively poor visual acuity in the periphery of the retina. In Fig. 10-6,II shows: on the left - diagrams of receptive fields illuminated in the center and along the periphery of the circle, on the right - diagrams of the frequency of APs arising in the axons of ganglion nerve cells in response to illumination. Under central illumination, the excited receptive field causes lateral inhibition along the periphery: in the upper figure on the right, the frequency of impulses in the center is much higher than at the edges. When the receptive field is illuminated along the edges of the circle, impulses are present at the periphery and absent in the center. Ganglion cells of different types. Ganglion cells at rest generate spontaneous potentials with a frequency of 5 to 40 Hz, which are superimposed by visual signals. Several types of ganglion neurons are known.

❖ W cells(perikaryon diameter<10 мкм, скорость проведения ПД 8 м/сек) составляют 40% от общего числа всех ганглиозных клеток. W-клетки имеют обширное рецептивное поле, они получают сигналы от палочек, передаваемые биполярными и амакринными клетками, и ответственны за сумеречное зрение.

❖ X cells(diameter 10-15 µm, conduction speed about 14 m/sec, 55%) have a small receptive field with discrete localization. They are responsible for the transmission of the visual image as such and all types of color vision.

❖ Y cells(diameter >35 µm, conduction velocity >50 m/sec, 5%) - the largest ganglion cells - have an extensive dendritic field and receive signals from various areas of the retina. Y cells respond to rapid changes in visual images, rapid movements in front of the eyes, and rapid changes in light intensity. These cells instantly signal to the central nervous system when a new visual image suddenly appears in any part of the visual field.

❖ on- and off-responses. Many ganglion neurons are excited by changes in light intensity. There are two types of responses: an on-response to turning on the light and an off-response to turning off the light. These different types of responses appear accordingly.

specifically from depolarized or hyperpolarized bipolars.

Color vision

Characteristics of color. Color has three main indicators: tone(shade), intensity And saturation. For each color there is additional(complementary) color which, when properly mixed with the original color, gives the appearance of white. Black color is the sensation created by the absence of light. The perception of white, any color of the spectrum, and even additional colors of the spectrum can be achieved by mixing red (570 nm), green (535 nm) and blue (445 nm) colors in various proportions. Therefore, red, green and blue - primary (primary) colors. The perception of color depends to some extent on the color of other objects in the visual field. For example, a red object will appear red if the field is illuminated with green or blue, and the same red object will appear pale pink or white if the field is illuminated with red.

Color perception- function of cones. There are three types of cones, each containing only one of three different (red, green and blue) visual pigments.

Trichromasia- the ability to distinguish any colors - is determined by the presence in the retina of all three visual pigments (for red, green and blue - primary colors). These fundamentals of the theory of color vision were proposed by Thomas Young (1802) and developed by Hermann Helmholtz.

NERVE PATHWAYS AND CENTERS

Visual pathways

The visual pathways are divided into old system where the midbrain and the base of the forebrain belong, and new system(to transmit visual signals directly to the visual cortex located in the occipital lobes). The new system is actually responsible for the perception of all visual images, color and all forms of conscious vision.

Main pathway to visual cortex(new system). Axons of ganglion cells in the optic nerves and (after the chiasm) in the optic tracts reach the lateral geniculate body (LCT, Fig. 10-7A). In this case, the fibers from the nasal half of the retina in the optic chiasm do not pass to the other side.

Figure 10-7. Visual pathways (A) and cortical centers (B). A. The areas of transection of the visual pathways are indicated by capital letters, and the visual defects that occur after transection are shown on the right. PP - optic chiasm. LCT - lateral geniculate body. KSHV - geniculate-spur fibers. B. The medial surface of the right hemisphere with the projection of the retina in the area of ​​the calcarine sulcus

Well. In the left LCT (ipsilateral eye), fibers from the nasal half of the retina of the left eye and fibers from the temporal half of the retina of the right eye synaptically contact LCT neurons, the axons of which form the geniculate calcarine tract (optic radiance). The geniculate calcarine fibers pass to the primary visual cortex of the same side. The paths from the right eye are organized similarly.

Other ways(old system). Axons of retinal ganglion neurons also pass to some ancient areas of the brain: ❖ to the supracrossus nuclei of the hypothalamus (control and synchronization of circadian rhythms); ❖ in the tegmental nuclei (reflexive eye movements when focusing an object, activation of the pupillary reflex); ❖ in the superior colliculus (control of rapid directed movements of both eyes); ❖ in the LCT and surrounding areas (control of behavioral reactions).

Lateral geniculate body(LCT) is part of the new visual system, where all the fibers passing through the optic tract end. LCT performs the function of transmitting information

from the optic tract to the visual cortex, precisely preserving the topology (spatial location) of different levels of paths from the retina (Fig. 10-7B). Another function of the LCT is to control the amount of information entering the cortex. Signals for the implementation of LCT input control enter the LCT in the form of feedback impulses from the primary visual cortex and from the reticular area of ​​the midbrain.

Visual cortex

The primary visual receptive area is located on the corresponding side of the calcarine sulcus (Fig. 10-7B). Like other parts of the neocortex, the visual cortex consists of six layers, the fibers of the geniculate calcarine tract ending predominantly in layer IV neurons. This layer is divided into sublayers that receive fibers from ganglion cells of type Y and X. In the primary visual cortex (Brodmann area 17) and visual area II (area 18), the three-dimensional arrangement of objects, the size of objects, the detail of objects and their color, and movement are analyzed objects, etc.

Columns and stripes. The visual cortex contains several million vertical primary columns, each column has a diameter of 30 to 50 μm and contains about 1000 neurons. Neuronal columns form intertwined strips 0.5 mm wide.

Color columnar structures. Among the primary visual columns, secondary areas are distributed - column-like formations (“color clots”). “Color clumps” receive signals from adjacent columns and are specifically activated by color signals.

Interaction of visual signals from the two eyes. Visual signals entering the brain remain separate until they enter layer IV of the primary visual cortex. Signals from one eye enter the columns of each strip, and the same happens with signals from the other eye. During the interaction of visual signals, the visual cortex deciphers the location of two visual images, finds their corresponding points (points in the same areas of the retina of both eyes) and adapts the decoded information to determine the distance to objects.

Specialization of neurons. In the columns of the visual cortex there are neurons that perform very specific functions (for example, analysis of contrast (including color), boundaries and directions of lines of the visual image, etc.).

PROPERTIES OF THE VISUAL SYSTEM Eye movements

External muscles of the eyeball. Eye movements are carried out by six pairs of striated muscles (Fig. 10-8A), coordinated by the brain through the III, IV, VI pairs of cranial nerves. If the rectus lateralis muscle of one eye contracts, the rectus medialis muscle of the other eye contracts by the same amount. The rectus superioris muscles work together to move the eyes back so that you can look up. The rectus inferior muscles enable you to look down. The superior oblique muscle rotates the eye downward and outward, and the inferior oblique muscle rotates the eye upward and outward.

ABOUT Convergence. The simultaneous and conjugal movement of both eyes allows, when looking at close objects, to bring them together (convergence).

ABOUT Divergence. Looking at distant objects leads to the separation of the visual axes of both eyes (divergence).

ABOUT Diplopia. Since the bulk of the visual field is binocular, it is clear that a high degree of coordination of movements of both eyes is necessary to maintain the visual image on the core.

Figure 10-8. External eye muscles. A. Ocular muscles of the left eye. B. Types of eye movements

responding points of both retinas and thereby avoid double vision (diplopia).

Types of movements. There are 4 types of eye movements (Fig. 10-8B).

ABOUT Saccades- imperceptible rapid jumps (in hundredths of a second) of the eye, tracing the contours of the image. Saccadic movements maintain the retention of the image on the retina, which is achieved by periodically shifting the image across the retina, resulting in the activation of new photoreceptors and new ganglion cells.

ABOUT Smooth Followers eye movements following a moving object.

ABOUT Converging movement - bringing the visual axes towards each other when viewing an object close to the observer. Each type of movement is controlled separately by the nervous apparatus, but ultimately all influences end on the motor neurons that innervate the external muscles of the eye.

ABOUT Vestibular eye movements are a regulatory mechanism that appears when the receptors of the semicircular canals are excited and maintains gaze fixation during head movements.

Physiological nystagmus. Even in conditions when the subject tries to fix a stationary object with his gaze, the eyeball continues to perform spasmodic and other movements (physiological nystagmus). In other words, the neuromuscular apparatus of the eye takes on the function of holding the visual image on the retina, since an attempt to hold the visual image motionless on the retina leads to its disappearance from the field of vision. That is why the need to constantly keep an object in the field of view requires a constant and rapid shift of the visual image across the retina.

CRITICAL FLICKING FREQUENCY. The eye retains traces of light stimulation for some time (150-250 ms) after the light is turned off. In other words, the eye perceives intermittent light as continuous at certain intervals between flashes. The minimum repetition rate of light stimuli at which individual flickering sensations merge into a sensation of continuous light is the critical flickering fusion frequency (24 frames per second). Television and cinema are based on this phenomenon: a person does not notice the gaps between individual frames, since the visual sensation from one frame continues until the appearance of another. This creates the illusion of image continuity and movement.

Aqueous moisture

Aqueous humor is continuously produced and reabsorbed. The balance between the formation and reabsorption of aqueous humor regulates the volume and pressure of intraocular fluid. Every minute, 2 to 3 µl of aqueous humor is formed. This fluid flows between the ligaments of the lens and then through the pupil into the anterior chamber of the eye. From here, the fluid enters the angle between the cornea and the iris, penetrates between the network of trabeculae into Schlemm's canal and pours into the external veins of the eyeball. Normal intraocular pressure the average is 15 mm Hg. with fluctuations between 12 and 20 mm Hg. The level of intraocular pressure is maintained constant with fluctuations of ±2 mm and is determined by the resistance to outflow from the anterior chamber into Schlemm's canal when fluid moves between the trabeculae, in which there are passages of 1-2 μm.

When exposed to light, electrical potentials are generated in the receptors, and then in the neurons of the retina [?], reflecting the parameters of the current stimulus. The total electrical response of the retina to light is called an electroretinogram (ERG). It can be recorded from the whole eye or directly from the retina. To do this, one electrode is placed on the surface of the cornea, and the other on the skin of the face near the eye or on the earlobe. On the electroretinogram, several characteristic waves are distinguished (Fig. 13.4).

Rice. 13.4. Electroretinogram (according to Gravit).

a, b, c, d - ERG waves; The arrows indicate the moments when the light flash turns on and off.

Wave a reflects the excitation of the internal segments of photoreceptors (late receptor potential) and horizontal cells. Wave b occurs as a result of activation of glial (Müller) cells of the retina by potassium ions released during excitation of bipolar and amacrine neurons. Wave With reflects the activation of pigment epithelial cells, and the wave d- horizontal cells.

The ERG clearly reflects the intensity, color, size and duration of action of the light stimulus. The amplitude of all ERG waves increases in proportion to the logarithm of the light intensity and the time during which the eye was in the dark. Wave d(response to switching off) is greater the longer the light is on. Since the ERG reflects the activity of almost all retinal cells (except ganglion cells), this indicator is widely used in the clinic of eye diseases for diagnosis and treatment monitoring for various retinal diseases.

Excitation of retinal ganglion cells leads to impulses being sent along their axons (optic nerve fibers) to the brain. The retinal ganglion cell is the first neuron of the “classical” type in the photoreceptor-brain circuit. Three main types of ganglion cells have been described: those that respond to turning the light on (on-reaction) and turning off the light (off-reaction), as well as to both (on-off-reaction) (Fig. 13.5). [!]

Rns. 13.5. [!] Impulse of two retinal ganglion cells and their concentric receptive fields. Inhibitory areas of receptive fields are shaded. Reactions to turning on and off the light when stimulated by a light spot of the center of the receptive field and its periphery are shown.

The diameter of the receptive fields of ganglion cells in the center of the retina is much smaller than in the periphery. These receptive fields are circular in shape and concentrically constructed: a round excitatory center and a circular inhibitory peripheral zone, or vice versa. As the size of the light spot flashing in the center of the receptive field increases, the response of the ganglion cell increases (spatial summation).

Simultaneous excitation of closely located ganglion cells leads to their mutual inhibition: the responses of each cell become smaller than with a single stimulation. This effect is based on lateral, or lateral, inhibition. Due to their circular shape, the receptive fields of retinal ganglion cells produce what is called a point-by-point description of the retinal image: it is displayed as a very fine mosaic of excited neurons.

Since 1945, electroretinography (ERG) has occupied a special place among functional research methods in the clinic of eye diseases. Along with well-known physiological and psychophysical methods, which provide data on the function of the visual analyzer along the entire visual path from the retina to the central parts, ERG is used to quantitatively assess the functional state of retinal neurons and more accurately determine the localization of the pathological process.

ERG is a graphical display of changes in the bioelectrical activity of the cellular elements of the retina in response to light stimulation. Photoreceptors transform light energy into nervous stimulation. Electrical potentials are generated in the receptors and then in the neurons of the retina, which occur when the amount of light increases or decreases.

The total electrical response of the retina to light is called electroretinograms. He may be recorded from the whole eye or directly from the retina. To record an electroretinogram one electrode is placed on the surface of the cornea, and the other is applied to the skin of the face near the eye or on the lobe (Fig. 27).

Fig.27. Bioelectric phenomena in the retina. A-scheme for recording an electroretinogram (ERG). 1-indifferent electrode (applied to the skin of the face near the eye or on the lobe), 2-active electrode. B-electroretinogram. P 1 – rod-dependent component; P 2 – reaction of bipolar cells; P 3 – inhibitory process in receptor cells.

In the total electroretinogram, several types of waves are distinguished: ( a, b, c, d) - rice. 28.

Figure 28. Electroretinogram ( according to Granite)

α - electronegative vibrations reflect the summation of potentials arising in photoreceptors and horizontal cells.

b- reflects changes in the membrane potentials of glial cells (Müller cells) of the retina by potassium ions upon excitation of bipolar and amacrine neurons.

With - reflects the biopotentials of pigment cells when the light is “turned on” (on-effect).

d- horizontal photoreceptor cells (and biopolar cells) when “turning off the light” (off-effect) (the longer the light is on, the greater it is .

General ERG reflects the electrical activity of most cellular elements of the retina and the dependence on the number of healthy functioning cells. Each ERG component is generated by different retinal structures. The result of the interaction of electrical activity of several processes is a-, b-, c-waves.

The ERG of the human eye contains negative a-wave, reflecting the function of photoreceptors as the initial part of the late receptor potential. On the descending part a-waves you can see two waves of very short latency - early receptor potentials (ERP), reflecting the cycle of biochemical transformations of rhodopsin. Wave A has a dual origin, corresponding to two types of photoreceptors. Earlier and 1 - the wave is associated with the activity of the photopic system of the retina, a 2-wave – with a scotopic system. Wave A turns positive b-wave, reflecting the electrical activity of bipolars and Müller cells with the possible contribution of horizontal and amacrine cells.

Wave b, or on-effect, reflects bioelectrical activity depending on the conditions of adaptation, the functions of the photopic and scotopic systems of the retina, which are represented in the positive component by waves b 1 and b 2. Most researchers linking the origin of the b-wave with the activity of bipolar cells and Müller cells, do not exclude the contribution of retinal ganglion cells. On the ascending part of the b-wave, there are 5-7 waves, called oscillatory potentials (OP), which reflect the interaction of cellular elements in the inner layers of the retina, including amacrine cells.

When the stimulus ceases (lights are turned off), it is recorded d-wave (off-effect). This wave, the last phase of the ERG, is the result of the interaction of the a-wave and the DC component of the b-wave. This wave, a mirror reflection of the a-wave, has photopic and scotopic phases. It is better recorded in the case of a predominance of cone elements in the retina. Thus, the main source of the α wave in the vertebrate ERG is thought to be photoreceptors, both cones and rods.

The following slow positive deviation with fast (45 sec) and slow (12 min) oscillation peaks is called c-wave, which can be isolated only when using stimuli that are continuously presented, high intensity and long duration in a dark-adapted eye. This is the transpigment potential of the epithelium, a slow positive potential of the extracellular current formed in connection with a change in the concentration of potassium, which is released when a microelectrode is inserted into the subretinal space. This slow potential is recorded indirectly using electrooculography. Currently, there is an opinion that the positive component With- The wave generated in the pigment epithelium layer represents the difference in hyperpolarization between the apical and basement membranes that occurs during light stimulation, and the negative component is recorded from Müller cells. Because With- the ERG wave persists in the absence of pigment epithelium, its origin is associated with the activity of photoreceptor cells, substances responsible for the light peak (EOG), transmitters (melatonin, dopamine) of photoreceptors. However With- the ERG wave cannot be recorded without normal physical and biochemical connections between the pigment epithelium and the outer segments of photoreceptors, renewal of discs, photochemical transformations of visual pigments and normal nutrition of the retina. Separation of the pigment epithelium from the outer segment of the photoreceptors, retinal detachment, leads to functional failure of the retina, accompanied by unrecordable ERG.

There are a number of criteria that determine the need for electrophysiological studies in the clinic of eye diseases:

1. The need to assess the functional state of the retina in cases where it is impossible to determine visual functions using the usual method, and the fundus of the eye is not ophthalmoscopically, in case of clouding of the media of the eye, hemophthalmia. Electroretinographic studies are especially valuable for deciding the advisability of surgical treatment of the disease.

2. Diagnosis of retinal diseases, since in some cases ERG measurements are pathognomonic symptoms of the disease.

3. Assessment of the depth, extent, extent of retinal damage and its location.

4. Study of the links in the pathogenesis of diseases of the retina and optic nerve.

5. Differential diagnosis of diseases of the retina and optic nerve of various origins.

6. Diagnosis of initial functional changes in the retina that precede clinical manifestations of the disease (drug intoxication, diabetic retinopathy, vascular disorders, etc.)

7. the need to determine the prognosis of the course of the pathological process, control over its evolution.