The central department of the visual analyzer structure and functions. Visual analyzer

visual analyzer. It is represented by the perceiving department - the receptors of the retina, the optic nerves, the conduction system and the corresponding areas of the cortex in the occipital lobes of the brain.

Eyeball(see figure) has spherical shape, enclosed in the eye socket. The auxiliary apparatus of the eye is represented by eye muscles, fatty tissue, eyelids, eyelashes, eyebrows, lacrimal glands. The mobility of the eye is provided by striated muscles, which at one end are attached to the bones of the orbital cavity, the other - to the outer surface of the eyeball - the albuginea. Two folds of skin surround the front of the eyes - eyelids. Their inner surfaces are covered with a mucous membrane - conjunctiva. The lacrimal apparatus consists of lacrimal glands and outflow tracts. A tear protects the cornea from hypothermia, drying out and washes away settled dust particles.

The eyeball has three shells: outer - fibrous, middle - vascular, inner - mesh. fibrous sheath opaque and is called protein or sclera. In front of the eyeball, it passes into a convex transparent cornea. Middle shell supplied with blood vessels and pigment cells. In front of the eye, it thickens, forming ciliary body, in the thickness of which there is a ciliary muscle, which changes the curvature of the lens with its contraction. The ciliary body passes into the iris, consisting of several layers. Pigment cells lie in a deeper layer. Eye color depends on the amount of pigment. There is a hole in the center of the iris - pupil, around which the circular muscles are located. When they contract, the pupil narrows. The radial muscles in the iris dilate the pupil. The innermost layer of the eye retina, containing rods and cones photosensitive receptors, representing the peripheral part of the visual analyzer. There are about 130 million rods and 7 million cones in the human eye. More cones are concentrated in the center of the retina, and rods are located around them and on the periphery. From photosensitive elements eyes (rods and cones), nerve fibers depart, which, connecting through intermediate neurons, form optic nerve. There are no receptors at the site of its exit from the eye, this area is not sensitive to light and is called blind spot. Outside of the blind spot, only cones are concentrated on the retina. This area is called yellow spot, it has the largest number of cones. The posterior retina is the bottom of the eyeball.

Behind the iris is a transparent body that has the shape of a biconvex lens - lens, able to refract light rays. The lens is enclosed in a capsule from which the ligaments of zinn extend and attach to the ciliary muscle. When the muscles contract, the ligaments relax and the curvature of the lens increases, it becomes more convex. The cavity of the eye behind the lens is filled with a viscous substance - vitreous body.

The emergence of visual sensations. Light stimuli are perceived by the rods and cones of the retina. Before reaching the retina, light rays pass through the refractive media of the eye. In this case, a real inverse reduced image is obtained on the retina. Despite the inverted image of objects on the retina, due to the processing of information in the cerebral cortex, a person perceives them in their natural position, moreover visual sensations are always supplemented and consistent with the readings of other analyzers.

The ability of the lens to change its curvature depending on the distance of the object is called accommodation. It increases when viewing objects at a close distance and decreases when the object is removed.

Eye dysfunctions include farsightedness And myopia. With age, the elasticity of the lens decreases, it becomes more flattened and accommodation weakens. At this time, a person sees well only distant objects: the so-called senile farsightedness develops. Congenital farsightedness is associated with a reduced size of the eyeball or a weak refractive power of the cornea or lens. In this case, the image from distant objects is focused behind the retina. When wearing glasses with convex lenses, the image moves to the retina. Unlike senile, with congenital farsightedness, the accommodation of the lens can be normal.

With myopia, the eyeball is enlarged in size, the image of distant objects, even in the absence of accommodation of the lens, is obtained in front of the retina. Such an eye clearly sees only close objects and is therefore called myopic. Glasses with concave glasses, moving the image to the retina, correct myopia.

receptors in the retina sticks and cones - differ in both structure and function. Cones are associated with daytime vision, they are excited in bright light, and twilight vision is associated with rods, since they are excited in low light. The sticks contain a red substance - visual Purple, or rhodopsin; in the light, as a result of a photochemical reaction, it decomposes, and in the dark it is restored within 30 minutes from the products of its own cleavage. That is why a person entering dark room, at first does not see anything, and after a while begins to gradually distinguish objects (by the time the synthesis of rhodopsin is completed). Vitamin A is involved in the formation of rhodopsin, with its deficiency, this process is disrupted and develops. "night blindness". The ability of the eye to see objects in different light levels is called adaptation. It is disturbed with a lack of vitamin A and oxygen, as well as with fatigue.

Cones contain another light-sensitive substance - iodopsin. It disintegrates in the dark and is restored in the light within 3-5 minutes. The breakdown of iodopsin in the presence of light gives color sensation. Of the two retinal receptors, only cones are sensitive to color, of which there are three types in the retina: some perceive red, others green, and others blue. Depending on the degree of excitation of the cones and the combination of stimuli, various other colors and their shades are perceived.

The eye should be protected from various mechanical influences, read in a well-lit room, holding the book at a certain distance (up to 33-35 cm from the eye). The light should fall on the left. You can not lean close to the book, since the lens in this position is in a convex state for a long time, which can lead to the development of myopia. Too bright lighting harms vision, destroys light-perceiving cells. Therefore, steelworkers, welders and other similar professions are advised to wear dark safety goggles while working. You can not read in a moving vehicle. Due to the instability of the position of the book, it changes all the time focal length. This leads to a change in the curvature of the lens, a decrease in its elasticity, as a result of which the ciliary muscle weakens. Visual impairment can also occur due to a lack of vitamin A.

Briefly:

The main part of the eye is the eyeball. It consists of the lens, vitreous body and aqueous humor. The lens has the appearance of a biconcave lens. It has the ability to change its curvature depending on the distance of the object. Its curvature is changed by the ciliary muscle. The function of the vitreous body is to maintain the shape of the eye. Also available aqueous humor two types: front and back. The anterior is between the cornea and the iris, and the posterior is between the iris and the lens. The function of the lacrimal apparatus is to moisten the eye. Myopia is a vision disorder in which an image forms in front of the retina. Farsightedness is a pathology in which the image is formed behind the retina. The image is formed inverted, reduced.

General structure of the visual analyzer

The visual analyzer consists of peripheral part , represented by the eyeball and auxiliary. part of the eye (eyelids, lacrimal apparatus, muscles) - for the perception of light and its transformation from a light impulse into an electrical one. pulse; pathways , including the optic nerve, optic tract, Graziola irradiance (to combine 2 images into one and conduct an impulse to the cortical zone), and central department analyzer. The central section consists of the subcortical center (external geniculate bodies) and the cortical visual center of the occipital lobe of the brain (for image analysis based on existing data).

The shape of the eyeball approaches spherical, which is optimal for the operation of the eye as an optical device, and ensures high mobility of the eyeball. This form is the most resistant to mechanical influences and is maintained by a fairly high intraocular pressure and the strength of the outer shell of the eye. Anatomically, two poles are distinguished - anterior and posterior. The straight line connecting both poles of the eyeball is called the anatomical or optical axis of the eye. The plane perpendicular to the anatomical axis and equidistant from the poles is the equator. Lines drawn through the poles around the eye are called meridians.

The eyeball has 3 membranes surrounding its internal environments - fibrous, vascular and reticular.

The structure of the outer shell. Functions

outer shell, or fibrous, represented by two departments: the cornea and sclera.

Cornea, is the anterior part of the fibrous membrane, occupying 1/6 of its length. The main properties of the cornea: transparency, specularity, avascularity, high sensitivity, sphericity. The horizontal diameter of the cornea is »11 mm, the vertical diameter is 1 mm shorter. Thickness in the central part 0.4-0.6 mm, on the periphery 0.8-1 mm. The cornea has five layers:

Anterior epithelium;

Anterior border plate, or Bowman's membrane;

Stroma, or own substance of the cornea;

Posterior border plate, or Descemet's membrane;

Posterior corneal epithelium.

Rice. 7. Scheme of the structure of the eyeball

Fibrous membrane: 1- cornea; 2 - limbus; 3-sclera. Vascular membrane:

4 - iris; 5 - pupil lumen; 6 - ciliary body (6a - flat part of the ciliary body; 6b - ciliary muscle); 7 - choroid. Inner shell: 8 - retina;

9 - dentate line; 10 - area yellow spot; 11 - optic disc.

12 - orbital part of the optic nerve; 13 - sheaths of the optic nerve. The contents of the eyeball: 14 - anterior chamber; 15 - rear camera;

16 - lens; 17- vitreous body. 18 - conjunctiva: 19 - extrinsic muscle

The cornea performs the following functions: protective, optical (>43.0 diopters), shaping, maintaining IOP.

The border of the transition of the cornea to the sclera is called limbus. This is a translucent zone with a width of »1mm.

Sclera occupies the remaining 5/6 of the length of the fibrous membrane. It is characterized by opacity and elasticity. The thickness of the sclera in the region of the posterior pole is up to 1.0 mm, near the cornea 0.6-0.8 mm. The thinnest place of the sclera is located in the area of ​​the passage of the optic nerve - the cribriform plate. The functions of the sclera include: protective (from exposure to damaging factors, lateral light of the retina), frame (skeleton of the eyeball). The sclera also serves as an attachment site for the oculomotor muscles.

Vascular tract of the eye, its features. Functions

Middle shell is called the vascular or uveal tract. It is divided into three sections: the iris, the ciliary body and the choroid.

Iris represents the anterior choroid. It has the appearance of a rounded plate, in the center of which there is a hole - the pupil. Its horizontal size is 12.5 mm, vertical 12 mm. The color of the iris depends on the pigment layer. The iris has two muscles: the sphincter, which constricts the pupil, and the dilator, which dilates the pupil.

Functions of the iris: shields light rays, is a diaphragm for the rays and is involved in the regulation of IOP.

ciliary, or ciliary body (corpus ciliare), has the form of a closed ring about 5-6 mm wide. On the inner surface of the anterior part of the ciliary body there are processes that produce intraocular fluid, the back part is flat. muscle layer represented by the ciliary muscle.

From the ciliary body stretches the ligament of cinnamon, or ciliary band, which supports the lens. Together they make up the accommodative apparatus of the eye. The border of the ciliary body with the choroid passes at the level of the dentate line, which corresponds on the sclera to the places of attachment of the rectus muscles of the eye.

Functions of the ciliary body: participation in accommodation (the muscular part with the ciliary girdle and lens) and the production of intraocular fluid (ciliary processes). Choroid, or the choroid itself, is back vascular tract. The choroid consists of layers of large, medium and small vessels. It is devoid of sensitive nerve endings, so the pathological processes developing in it do not cause pain.

Its function is trophic (or nutritional), i.e. it is the energy base that ensures the restoration of the continuously decaying visual pigment necessary for vision.

The structure of the lens.

lens is a transparent biconvex lens with a refractive power of 18.0 diopters. The lens diameter is 9-10 mm, thickness is 3.5 mm. It is isolated from the rest of the membranes of the eye by a capsule and does not contain nerves and blood vessels. It consists of lens fibers that make up the substance of the lens, and a bag-capsule and capsular epithelium. Fiber formation occurs throughout life, which leads to an increase in the volume of the lens. But there is no excessive increase, because. old fibers lose water, condense, and a compact core forms in the center. Therefore, it is customary to distinguish the nucleus (consisting of old fibers) and the cortex in the lens. Functions of the lens: refractive and accommodative.

drainage system

The drainage system is the main way of outflow of intraocular fluid.

Intraocular fluid is produced by processes of the ciliary body.

Hydrodynamics of the eye - The transition of intraocular fluid from the posterior chamber, where it first enters, to the anterior one, normally does not encounter resistance. Of particular importance is the outflow of moisture through

the drainage system of the eye, located in the corner of the anterior chamber (the place where the cornea passes into the sclera, and the iris into the ciliary body) and consisting of the trabecular apparatus, Schlemm's canal, collector-

channels, systems of intra- and episcleral venous vessels.

The trabecula has a complex structure and consists of the uveal trabecula, the corneoscleral trabecula, and the juxtacanalicular layer.

The outermost, juxtacanalicular layer differs significantly from the others. It is a thin diaphragm epithelial cells and a loose system of collagen fibers impregnated with muco-

lisaccharides. That part of the resistance to the outflow of intraocular fluid, which falls on the trabeculae, is located in this layer.

Schlemm's canal is a circular slit located in the limbus zone.

The function of the trabeculae and Schlemm's canal is to maintain a constant intraocular pressure. Violation of the outflow of intraocular fluid through the trabeculae is one of the main causes of primary

glaucoma.

visual path

Topographically, the optic nerve can be divided into 4 sections: intraocular, intraorbital, intraosseous (intracanal) and intracranial (intracerebral).

The intraocular part is represented by a disk with a diameter of 0.8 mm in newborns and 2 mm in adults. The color of the disc is yellowish-pink (grayish in young children), its contours are clear, in the center there is a funnel-shaped depression of a whitish color (excavation). In the excavation area, the central retinal artery enters and the central retinal vein exits.

The intraorbital part of the optic nerve, or its initial pulpy section, begins immediately after exiting the lamina cribrosa. It immediately acquires a connective tissue (soft shell, delicate arachnoid sheath and outer (hard) shell. The optic nerve (n. opticus), covered with

locks. The intraorbital part has a length of 3 cm and an S-shaped bend. Such

size and shape contribute to good eye mobility without tension on the optic nerve fibers.

The intraosseous (intratubular) part of the optic nerve starts from the visual opening of the sphenoid bone (between the body and the roots of its small

wing), passes through the canal and ends at the intracranial opening of the canal. The length of this segment is about 1 cm. It loses in the bone canal hard shell

and is covered only with soft and arachnoid shells.

The intracranial section has a length of up to 1.5 cm. In the region of the diaphragm of the Turkish saddle, the optic nerves merge, forming a cross - the so-called

chiasma. The fibers of the optic nerve from the outer (temporal) parts of the retina of both eyes do not cross and go along the outer sections of the chiasm posteriorly, but

curls from the internal (nasal) parts of the retina are completely crossed.

After a partial intersection of the optic nerves in the region of the chiasm, the right and left optic tracts are formed. Both optic tracts, diverging, onto

head to the subcortical visual centers - the lateral geniculate bodies. In the subcortical centers, the third neuron closes, starting in the multipolar cells of the retina, and the so-called peripheral part of the visual pathway ends.

Thus, the optic pathway connects the retina with the brain and is formed from the axons of ganglion cells, which, without interruption, reach the lateral geniculate body, the posterior part of the optic tubercle and the anterior quadrigemina, as well as from centrifugal fibers, which are elements feedback. The subcortical center is the external geniculate body. In the lower temporal part of the optic disc, the fibers of the papillomacular bundle are concentrated.

The central part of the visual analyzer starts from large long-axon cells of the subcortical visual centers. These centers are connected by visual radiation with the cortex of the spur groove on

medial surface of the occipital lobe of the brain, while passing the posterior leg of the internal capsule, which corresponds mainly to field 17 according to Brodmann of the cortex

brain. This zone is the central part of the core of the visual analyzer. If fields 18 and 19 are damaged, spatial orientation is disturbed or “spiritual” (mental) blindness occurs.

Blood supply to the optic nerve to the chiasm carried out by branches of the internal carotid artery. The blood supply to the intraocular part of the visual

th nerve is carried out from 4 arterial systems: retinal, choroidal, scleral and meningeal. The main sources of blood supply are the branches of the ophthalmic artery (central ar-

teria of the retina, posterior short ciliary arteries), branches of the plexus of the pia mater. Prelaminar and laminar sections of the visual disk

The corpus nerve is fed from the system of the posterior ciliary arteries.

Although these arteries are not of the terminal type, the anastomoses between them are insufficient and the blood supply to the choroid and disc is segmental. Consequently, when one of the arteries is occluded, the nutrition of the corresponding segment of the choroid and the optic nerve head is disrupted.

Thus, turning off one of the posterior ciliary arteries or its small branches will turn off the sector of the cribriform plate and prelaminar

part of the disk, which will manifest itself as a kind of loss of visual fields. This phenomenon is observed with anterior ischemic opticopathy.

The main sources of blood supply to the cribriform plate are the posterior short ciliary

arteries. The vessels that feed the optic nerve belong to the system of the internal carotid artery. Branches of the external carotid artery have numerous anastomoses with branches of the internal carotid artery. Almost the entire outflow of blood, both from the vessels of the optic nerve head and from the retrolaminar region, is carried out into the system of the central retinal vein.

Conjunctivitis

Inflammatory diseases of the conjunctiva.

Bacterial to-t. Complaints: photophobia, lacrimation, burning sensation and heaviness in the eyes.

Wedge. Manifestations: pronounced conjunctiva. Injection (red eye), profuse mucopurulent discharge, edema. The disease starts in one eye and moves to the other eye.

Complications: punctate gray corneal infiltrates, cat. rasp. chain around the limbus.

Treatment: frequent washing of eyes des. solutions, frequent instillation of drops, ointments for complications. After the subsidence of resp. Hormones and NSAIDs.

Viral to-t. Complaints: Air-cap. transmission path. O. beginning, often preceded by catarrhal manifestations of the upper respiratory tract. Raise pace. body, runny nose, goal. Pain, stole l / nodes, photophobia, lacrimation, little or no discharge, hyperemia.

Complications: punctate epithelial keratitis, favorable outcome.

Treatment: Antivirus. drugs, ointments.

Building of the century. Functions

Eyelids (palpebrae) are mobile external formations that protect the eye from external influences during sleep and wakefulness (Fig. 2.3).

Rice. 2. Scheme of the sagittal section through the eyelids and

anterior eyeball

1 and 5 - upper and lower conjunctival arches; 2 - conjunctiva of the eyelid;

3 - cartilage of the upper eyelid with meibomian glands; 4 - skin of the lower eyelid;

6 - cornea; 7 - anterior chamber of the eye; 8 - iris; 9 - lens;

10 - zinn ligament; 11 - ciliary body

Rice. 3. Sagittal section of the upper eyelid

1,2,3,4 - eyelid muscle bundles; 5.7 - additional lacrimal glands;

9 - rear edge of the eyelid; 10 - excretory duct of the meibomian gland;

11 - eyelashes; 12 - tarsoorbital fascia (behind it adipose tissue)

Outside they are covered with skin. The subcutaneous tissue is loose and devoid of fat, which explains the ease of edema. Under the skin is the circular muscle of the eyelids, due to which the palpebral fissure closes and the eyelids close.

Behind the muscle is cartilage of the eyelid (tarsus), in the thickness of which there are meibomian glands that produce a fatty secret. Their excretory ducts exit as pinpoint openings into the intermarginal space - a strip of a flat surface between the anterior and posterior ribs of the eyelids.

Eyelashes grow in 2-3 rows on the front rib. The eyelids are connected by external and internal adhesions, forming the palpebral fissure. The inner corner is blunted by a horseshoe-shaped bend that limits the lacrimal lake, which contains the lacrimal caruncle and the lunate fold. The length of the palpebral fissure is about 30 mm, the width is 8-15 mm. The back surface of the eyelids is covered with a mucous membrane - the conjunctiva. In front, it passes into the corneal epithelium. The place of transition of the conjunctiva of the eyelid into the conjunctiva of Ch. apples - vault.

Functions: 1. Protection against mechanical damage

2. moisturizing

3. participates in the process of tear formation and tear film formation

Barley

Barley- acute purulent inflammation of the hair follicle. It is characterized by the appearance of painful redness and swelling on a limited area of ​​​​the edge of the eyelid. After 2-3 days, a purulent point appears in the center of inflammation, a purulent pustule is formed. On the 3-4th day, it opens, and purulent contents come out of it.

At the very beginning of the disease, the painful point should be smeared with alcohol or 1% solution of brilliant green. With the development of the disease - antibacterial drops and ointments, FTL, dry heat.

Blepharitis

Blepharitis- inflammation of the edges of the eyelids. The most common and persistent disease. The occurrence of blepharitis is promoted by unfavorable sanitary and hygienic conditions, allergic condition organism, uncorrected refractive errors, the introduction of Demodex mite into the hair follicle, increased secretion of the meibomian glands, gastrointestinal diseases.

Blepharitis begins with reddening of the edges of the eyelids, itching and foamy discharge in the corners of the eyes, especially in the evening. Gradually, the edges of the eyelids thicken, covered with scales and crusts. Itching and feeling of clogging of the eyes are intensified. If left untreated, bleeding ulcers form at the root of the eyelashes, the nutrition of the eyelashes is disrupted, and they fall out.

Treatment of blepharitis includes the elimination of factors contributing to its development, the toilet of the eyelids, massage, the application of anti-inflammatory and vitamin ointments.

Iridocyclitis

Iridocyclitis begin with irita- inflammation of the iris.

Clinical picture iridocyclitis manifests itself primarily sharp pain in the eye and corresponding half of the head, worse at night. By-

the phenomenon of pain is associated with irritation of the ciliary nerves. Irritation of the ciliary nerves in a reflex way causes the appearance photophobia(blepharospasm and lacrimation). Maybe visual impairment, although vision may be normal early in the disease.

With developed iridocyclitis the color of the iris changes

due to an increase in the permeability of the dilated vessels of the iris and the entry of erythrocytes into the tissue, which are destroyed. This, as well as infiltration of the iris, explains two other symptoms - shading of the picture irises and miosis - pupil constriction.

With iridocyclitis appears pericorneal injection. The pain reaction to light intensifies at the moment of accommodation and convergence. To determine this symptom, the patient should look into the distance, and then quickly at the tip of his nose; this causes severe pain. In unclear cases, this factor, among other signs, contributes to the differential diagnosis with conjunctivitis.

Almost always with iridocyclitis are determined precipitates, settling on the posterior surface of the cornea in the lower half in the form of a triangle apex

noah up. They are lumps of exudate containing lymphocytes, plasma cells, macrophages.

The next important symptom of iridocyclitis is the formation posterior synechia- adhesions of the iris and the anterior lens capsule. Swell-

neck, the inactive iris is in close contact with the anterior surface of the lens capsule, therefore, a small amount of exudate, especially fibrinous, is sufficient for fusion.

When measuring intraocular pressure, normo- or hypotension is ascertained (in the absence of secondary glaucoma). Perhaps a reactive increase in

eye pressure.

Last constant symptom iridocyclitis is the appearance exudate in the vitreous body causing diffuse or flaky floaters.

Choroiditis

Choroiditis characterized by the absence of pain. There are complaints characteristic of the defeat back section eyes: flashes and flickering before the eye (photopsia), distortion of the objects in question (metamorphopsia), deterioration of twilight vision (hemeralopia).

For diagnosis, an examination of the fundus is necessary. With ophthalmoscopy, foci of a yellowish-gray color, of various shapes and sizes, are visible. There may be hemorrhages.

Treatment includes general therapy (aimed at the underlying disease), injections of corticosteroids, antibiotics, PTL.

Keratitis

Keratitis- inflammation of the cornea. Depending on the origin, they are divided into traumatic, bacterial, viral, keratitis with infectious diseases and avitaminosis. Viral herpetic keratitis is the most severe.

Despite the diversity clinical forms, keratitis has a number common symptoms. Among the complaints are pain in the eye, photophobia, lacrimation, decreased visual acuity. Examination reveals blepharospasm, or eyelid contraction, pericorneal injection (most pronounced around the cornea). There is a decrease in the sensitivity of the cornea up to its complete loss - with herpetic. Keratitis is characterized by the appearance of opacities on the cornea, or infiltrates, which ulcerate, forming ulcers. Against the background of treatment, ulcers are performed with opaque connective tissue. Therefore, after deep keratitis, persistent opacities are formed. different intensity. And only superficial infiltrates completely resolve.

1. Bacterial keratitis.

Complaints: pain, photophobia, lacrimation, red eye, corneal infiltrates with progrowth. vessels, purulent ulcer with undermined edge, hypopion (pus in the anterior chamber).

Outcome: perforation outward or inward, clouding of the cornea, panophthalmitis.

Treatment: Hospital quickly!, A / b, GCC, NSAIDs, DTC, keratoplasty, etc.

2 viral keratitis

Complaints: lower feelings of the cornea, corneal s-m expressed insignificantly, in the beginning. stage discharge scanty, relapse. flow x-r, preceding herpes. Rashes, rarely vascularization of infiltrates.

Outcome: recovery; cloudy-thin translucent limited opacity of a grayish color, invisible to the naked eye; spot - a denser limited whitish clouding; thorn is a dense thick opaque scar of the cornea of ​​​​white color. Spots and clouds can be removed with a laser. Belmo – keratoplasty, keratoprosthetics.

Treatment: stat. or amb., p / viral, NSAIDs, a / b, mydriatics, cryo-, laser-, keratoplasty, etc.

Cataract

Cataract- any clouding of the lens (partial or complete), occurs as a result of a violation of metabolic processes in it during age-related changes or diseases.

According to localization, cataracts are anterior and posterior polar, fusiform, zonular, bowl-shaped, nuclear, cortical and total.

Classification:

1. By origin - congenital (limited and does not progress) and acquired (senile, traumatic, complicated, radiation, toxic, against the background of general diseases)

2. By localization - nuclear, capsular, total)

3. According to the degree of maturity (initial, immature, mature, overripe)

Causes: metabolic disorders, intoxication, irradiation, concussions, penetrating wounds, eye diseases.

age cataract develops as a result of dystrophic processes in the lens and localization can be cortical (most often), nuclear or mixed.

With cortical cataract, the first signs appear in the cortex of the lens near the equator, and the central part remains transparent for a long time. This helps to maintain a relatively high visual acuity for a long time. IN clinical course four stages are distinguished: initial, immature, mature and overripe.

With the initial cataract, patients are concerned about complaints of decreased vision, "flying flies", "fog" before the eyes. Visual acuity is in the range of 0.1-1.0. In the study in transmitted light, the cataract is visible in the form of black "spokes" from the equator to the center against the background of the red glow of the pupil. The fundus of the eye is available for ophthalmoscopy. This stage can last from 2-3 years to several decades.

At the stage of immature, or swelling, cataract, the patient's visual acuity sharply decreases, since the process captures the entire cortex (0.09-0.005). As a result of hydration of the lens, its volume increases, which leads to myopization of the eye. In lateral illumination, the lens has a gray-white color and a "lunar" shadow is noted. In transmitted light, the fundus reflex is unevenly dim. Swelling of the lens leads to a decrease in the depth of the anterior chamber. If the angle of the anterior chamber is blocked, then IOP rises, an attack of secondary glaucoma develops. The fundus of the eye is not ophthalmoscoped. This stage can last indefinitely.

With a mature cataract, objective vision completely disappears, only light perception with the correct projection is determined (VIS=1/¥Pr.certa.). The fundus reflex is grey. In side illumination, the entire lens is white-gray.

The stage of overmature cataract is divided into several stages: the phase of the milk cataract, the phase of the morganian cataract and complete resorption, as a result of which only one capsule remains from the lens. The fourth stage practically does not occur.

In the process of cataract maturation, the following complications may occur:

Secondary glaucoma (phacogenous) - due to the pathological condition of the lens in the stage of immature and overripe cataracts;

Phacotoxic iridocyclitis - due to the toxic-allergic effect of the decay products of the lens.

Treatment of cataracts is divided into conservative and surgical.

A conservative one is prescribed to prevent the progression of cataracts, which is advisable at the first stage. It includes vitamins in drops (complex B, C, P, etc.), combined preparations(sencatalin, catachrom, quinax, withiodurol, etc.) and drugs that affect metabolic processes in the eye (4% solution of taufon).

Surgical treatment consists in surgical removal of the cloudy lens (cataract extraction) and phacoemulsification. Cataract extraction can be carried out in two ways: intracapsular - extraction of the lens in the capsule and extracapsular - removal of the anterior capsule, nucleus and lens masses while maintaining the posterior capsule.

Usually surgical treatment carried out at the stage of immature, mature or overripe cataracts and with complications. An initial cataract is sometimes operated on for social reasons (for example, professional mismatch).

Glaucoma

Glaucoma is an eye disease characterized by:

Constant or periodic increase in IOP;

The development of atrophy of the optic nerve (glaucomatous excavation of the optic disc);

Occurrence of typical visual field defects.

With an increase in IOP, the blood supply to the membranes of the eye suffers, especially sharply to the intraocular part of the optic nerve. As a result, atrophy of its nerve fibers develops. This, in turn, leads to the appearance of typical visual defects: a decrease in visual acuity, the appearance of paracentral scotomas, an increase in the blind spot, and a narrowing of the visual field (especially from the nasal side).

There are three main types of glaucoma:

Congenital - due to anomalies in the development of the drainage system,

Primary, as a result of a change in the angle of the anterior chamber (ACC),

Secondary, as a symptom of eye diseases.

Primary glaucoma is the most common. Depending on the state of the CPC, it is divided into open-angle, closed-angle and mixed.

Open angle glaucoma is a consequence dystrophic changes in the drainage system of the eye, which leads to a violation of the outflow of intraocular fluid through the APC. It is characterized by an imperceptible chronic course against the background of moderately elevated IOP. Therefore, it is often detected by chance during examinations. On gonioscopy, the APC is open.

Angle-closure glaucoma occurs as a result of blockade of the APC by the root of the iris, due to the functional block of the pupil. This is due to the tight fit of the lens to the iris as a result of the anatomical features of the eye: a large lens, a small anterior chamber, a narrow pupil in the elderly. This form of glaucoma is characterized by a paroxysmal course and begins with an acute or subacute attack.

Mixed glaucoma is a combination of features typical of the two previous forms.

There are four stages in the development of glaucoma: initial, advanced, advanced and terminal. The stage depends on the state of visual functions and ONH.

The initial, or stage I, is characterized by an expansion of the disc excavation up to 0.8, an increase in the blind spot and paracentral scotomas, and a slight narrowing of the visual field from the nasal side.

In advanced, or stage II, there is marginal excavation of the ONH and a persistent narrowing of the visual field from the nasal side to 15° from the point of fixation.

Far advanced, or stage III, is characterized by a persistent concentric narrowing of the field of view less than 15 0 from the point of fixation or preservation individual sections fields of view.

At the terminal, or IV stage, there is a loss of object vision - the presence of light perception with an incorrect projection (VIS=1/¥ pr/incerta) or complete blindness (VIS=0).

Acute attack of glaucoma

An acute attack occurs with angle-closure glaucoma as a result of blocking the lens of the pupil. This disrupts the outflow of intraocular fluid from the posterior chamber to the anterior chamber, which leads to an increase in IOP in the posterior chamber. The consequence of this is the extrusion of the iris anteriorly (“bombing”) and the closure of the iris by the root of the APC. Outflow through the drainage system of the eye becomes impossible, and IOP rises.

Acute attacks of glaucoma usually occur under the influence of stressful conditions, physical overstrain, with medical dilation of the pupil.

During an attack, the patient complains of sharp pains in the eye, radiating to the temple and the corresponding half of the head, blurred vision and the appearance of iridescent circles when looking at the light source.

On examination, there is a congestive injection of the vessels of the eyeball, corneal edema, a shallow anterior chamber, and a wide oval pupil. The rise in IOP can be up to 50-60 mm Hg and above. On gonioscopy, the APC is closed.

Treatment should be carried out as soon as the diagnosis is established. Local instillations of miotics are carried out (1% solution of pilocarpine during the first hour - every 15 minutes, II-III hour - every 30 minutes, IV-V hour - 1 time per hour). Inside - diuretics (diacarb, lasix), analgesics. Distraction therapy includes hot foot baths. In all cases, hospitalization is required for surgical or laser treatment.

Glaucoma treatment

Conservative treatment of glaucoma consists of antihypertensive therapy, that is, a decrease in IOP (1% solution of pilocarpine, timolol.) And drug treatment aimed at improving blood circulation and metabolic processes in the tissues of the eye (vasodilator drugs, angioprotectors, vitamins).

Surgical and laser treatment subdivided into several methods.

Iridectomy - excision of a section of the iris, as a result of which the consequences of the pupillary block are eliminated.

Operations on the scleral sinus and trabeculae: sinusotomy - opening the outer wall of the Schlemm's canal, trabeculotomy - an incision in the inner wall of the Schlemm's canal, sinus trabeculoectomy - excision of the trabecula and sinus.

Fistulizing operations - the creation of new outflow tracts from the anterior chamber of the eye to the subconjunctival space.

Clinical refraction

physical refraction- the refractive power of any optical system. To obtain a clear image, it is not the refractive power of the eye that is important, but its ability to focus the rays exactly on the retina. Clinical refraction is the ratio of the main focus to the center. retinal fossa.

Depending on this ratio, refraction is divided into:

Proportionate - emmetropia;

Disproportionate - ametropia

Every kind clinical refraction characterized by the position of the further point of clear vision.

Further point of clear vision (Rp) is a point in space, the image of which is focused on the retina at rest of accommodation.

emmetropia- a type of clinical refraction in which the rear main focus of parallel rays is on the retina, i.e. refractive power is proportional to the length of the eye. The next point of clear vision is at infinity. Therefore, the image of distant objects is clear, and visual acuity is high. Ametropia- clinical refraction, in which the back main focus of parallel rays does not coincide with the retina. Depending on its location, ametropia is divided into myopia and hypermetropia.

Classification of ametropia (according to Throne):

Axial - the refractive power of the eye is within the normal range, and the length of the axis is greater or less than with emmetropia;

Refractive - the length of the axis is within the normal range, the refractive power of the eye is greater or less than with emmetropia;

Mixed origin - the length of the axis and the refractive power of the eye does not correspond to the norm;

Combination - the length of the axis and the refractive power of the eye are normal, but their combination is unsuccessful.

Myopia- a type of clinical refraction in which the back main focus is in front of the retina, therefore, the refractive power is too high and does not correspond to the length of the eye. Therefore, in order for the rays to be collected on the retina, they must have a divergent direction, that is, a further point of clear vision is located in front of the eye at a finite distance. Visual acuity in myopes is reduced. The closer Rp lies to the eye, the stronger the refraction and the higher the degree of myopia.

Degrees of myopia: weak - up to 3.0 diopters, medium - 3.25-6.0 diopters, high - above 6.0 diopters.

Hypermetropia- a type of ametropia, in which the back main focus is behind the retina, that is, the refractive power is too small.

In order for the rays to be collected on the retina, they must have a converging direction, that is, a further point of clear vision is located behind the eye, which is only theoretically possible. The farther behind the eye is Rp, the weaker the refraction and the higher the degree of hypermetropia. The degrees of hypermetropia are the same as in myopia.

Myopia

The reasons for the development of myopia include: heredity, elongation of the lateral eye of the eye, primary weakness of accommodation, weakening of the sclera, prolonged work at close range, and the natural and geographical factor.

Scheme of pathogenesis: -weakening of accommodation

Spasm of accommodation

False M

Development of true M or progression of existing M

The emmetropic eye becomes myopic, not because it accommodates, but because it is difficult for it to accommodate for a long time.

With weakened accommodation, the eye can lengthen to such an extent that, under conditions of intense visual work at close range, the ciliary muscle is generally relieved of excessive activity. With an increase in the degree of myopia, an even greater weakening of accommodation is observed.

The weakness of the ciliary muscle is due to the lack of its blood circulation. And the increase in the eye's PZO is accompanied by an even greater deterioration in local hemodynamics, which leads to an even greater weakening of accommodation.

The percentage of myopes in the regions of the Arctic is higher than in the middle lane. Myopia is more common among urban schoolchildren than among rural schoolchildren.

Distinguish between true myopia and false.

true myopia

Classification:

1. According to the age period of occurrence:

congenital,

Acquired.

2. Downstream:

Stationary,

Slowly progressing (less than 1.0 diopters per year),

Rapidly progressing (more than 1.0 diopters per year).

3. According to the presence of complications:

uncomplicated,

Complicated.

Acquired myopia is a variant of clinical refraction, which, as a rule, increases slightly with age and is not accompanied by noticeable morphological changes. It is well corrected and does not require treatment. An unfavorable prognosis is usually noted only with myopia acquired at preschool age, since the scleral factor plays a role.

For most people, the concept of "vision" is associated with the eyes. In fact, the eyes are only part of complex organ, called in medicine a visual analyzer. The eyes are only a conductor of information from the outside to the nerve endings. And the very ability to see, to distinguish colors, sizes, shapes, distance and movement is provided precisely by the visual analyzer - a system of complex structure, which includes several departments that are interconnected.

Knowledge of the anatomy of the human visual analyzer allows you to correctly diagnose various diseases, determine their cause, choose the right treatment tactics, and carry out complex surgical operations. Each of the departments of the visual analyzer has its own functions, but they are closely interconnected with each other. If at least one of the functions of the organ of vision is disturbed, this invariably affects the quality of perception of reality. You can restore it only by knowing where the problem is hidden. That is why knowledge and understanding of the physiology of the human eye is so important.

Structure and departments

The structure of the visual analyzer is complex, but it is thanks to this that we can perceive the world so bright and full. It consists of the following parts:

• Peripheral - here are the receptors of the retina.
• The conductive part is the optic nerve.
• The central section - the center of the visual analyzer is localized in the occipital part of the human head.

The work of the visual analyzer can in essence be compared with a television system: an antenna, wires and a TV

The main functions of the visual analyzer are the perception, conduction and processing of visual information. The eye analyzer does not work primarily without the eyeball - this is its peripheral part, which accounts for the main visual functions.

The scheme of the structure of the immediate eyeball includes 10 elements:

• the sclera is the outer shell of the eyeball, relatively dense and opaque, it has blood vessels and nerve endings, it connects in front to the cornea, and in the back to the retina;
• choroid - provides a conductor of nutrients along with blood to the retina of the eye;
• retina - this element, consisting of photoreceptor cells, ensures the sensitivity of the eyeball to light. There are two types of photoreceptors - rods and cones. Rods are responsible for peripheral vision, they are highly photosensitivity. Thanks to rod cells, a person is able to see at dusk. The functional feature of cones is completely different. They allow the eye to perceive different colors and fine details. The cones are responsible for central vision. Both types of cells produce rhodopsin, a substance that converts light energy into electrical energy. It is she who is able to perceive and decipher the cortical part of the brain;
• The cornea is the transparent part of the anterior part of the eyeball where light is refracted. The peculiarity of the cornea is that there are no blood vessels in it at all;
• The iris is optically the brightest part of the eyeball, the pigment responsible for the color of the human eye is concentrated here. The more it is and the closer it is to the surface of the iris, the darker the eye color will be. Structurally, the iris is a muscle fiber that is responsible for the contraction of the pupil, which in turn regulates the amount of light transmitted to the retina;
• ciliary muscle - sometimes called the ciliary girdle, main characteristic this element is the adjustment of the lens, so that a person’s gaze can quickly focus on one object;
• The lens is a transparent lens of the eye, its main task is to focus on one object. The lens is elastic, this property is enhanced by the muscles surrounding it, due to which a person can clearly see both near and far;
• The vitreous body is a transparent gel-like substance that fills the eyeball. It is it that forms its rounded, stable shape, and also transmits light from the lens to the retina;
• the optic nerve is the main part of the information pathway from the eyeball to the area of ​​the cerebral cortex that processes it;
• the yellow spot is the area of ​​maximum visual acuity, it is located opposite the pupil above the entry point of the optic nerve. The spot got its name for the high content of yellow pigment. It is noteworthy that some birds of prey, differing sharp eyesight, have as many as three yellow spots on the eyeball.

The periphery collects the maximum of visual information, which is then transmitted through the conductive section of the visual analyzer to the cells of the cerebral cortex for further processing.

This is how the structure of the eyeball looks schematically in section

Auxiliary elements of the eyeball

The human eye is mobile, which allows you to capture a large amount of information from all directions and quickly respond to stimuli. Mobility is provided by the muscles covering the eyeball. There are three pairs in total:

• A pair that moves the eye up and down.
• A pair responsible for moving left and right.
• A pair due to which the eyeball can rotate about the optical axis.

This is enough for a person to be able to look in a variety of directions without turning his head, and quickly respond to visual stimuli. Muscle movement is provided by the oculomotor nerves.

Also auxiliary elements of the visual apparatus include:

• eyelids and eyelashes;
• conjunctiva;
• lacrimal apparatus.

Eyelids and eyelashes perform protective function, forming a physical barrier to the penetration of foreign bodies and substances, exposure to too bright light. The eyelids are elastic plates of connective tissue, covered on the outside with skin, and on the inside with conjunctiva. The conjunctiva is the mucous membrane that lines the inside of the eye and eyelid. Its function is also protective, but it is provided by the development of a special secret that moisturizes the eyeball and forms an invisible natural film.

The human visual system is complex, but quite logical, each element has a specific function and is closely related to others.

The lacrimal apparatus is the lacrimal glands, from which the lacrimal fluid is excreted through the ducts into the conjunctival sac. The glands are paired, they are located in the corners of the eyes. Also in the inner corner of the eye is a lacrimal lake, where a tear flows after it has washed the outer part of the eyeball. From there, the tear fluid passes into the nasolacrimal duct and drains into the lower parts of the nasal passages.

It's natural and ongoing process, not perceptible by humans. But when too much tear fluid is produced, the tear-nasal duct is not able to receive it and move it all at the same time. The liquid overflows over the edge of the lacrimal lake - tears are formed. If, on the contrary, for some reason, the tear fluid is produced too little or it cannot move through tear ducts due to their blockage, dry eyes occur. A person feels severe discomfort, pain and pain in the eyes.

How is the perception and transmission of visual information

To understand how the visual analyzer works, it is worth imagining a TV and an antenna. The antenna is the eyeball. It reacts to the stimulus, perceives it, converts it into an electrical wave and transmits it to the brain. This is done through the conductive section of the visual analyzer, which consists of nerve fibers. They can be compared to a television cable. The cortical region is a TV, it processes the wave and decodes it. The result is a visual image familiar to our perception.

Human vision is much more complex and more than just eyes. This is a complex multi-stage process, carried out thanks to the coordinated work of the group. various bodies and elements

It is worth considering the conduction department in more detail. It consists of crossed nerve endings, that is, information from the right eye goes to the left hemisphere, and from the left to the right. Why exactly? Everything is simple and logical. The fact is that for optimal decoding of the signal from the eyeball to the cortical section, its path should be as short as possible. The area in the right hemisphere of the brain responsible for decoding the signal is located closer to the left eye than to the right. And vice versa. This is why signals are transmitted over criss-cross paths.

Crossed nerves further form the so-called optic tract. Here, information from different parts of the eye is transmitted for decoding to different parts of the brain, so that a clear visual picture is formed. The brain can already determine the brightness, degree of illumination, color gamut.

What happens next? The almost completely processed visual signal enters the cortical region, it remains only to extract information from it. This is the main function of the visual analyzer. Here are carried out:

• perception of complex visual objects, for example, printed text in a book;
• assessment of the size, shape, remoteness of objects;
• formation of perspective perception;
• the difference between flat and voluminous objects;
• combining all the information received into a coherent picture.

So, thanks to the coordinated work of all departments and elements of the visual analyzer, a person is able not only to see, but also to understand what he sees. Those 90% of the information that we receive from the outside world through the eyes comes to us in just such a multi-stage way.

How does the visual analyzer change with age

The age features of the visual analyzer are not the same: in a newborn it is not yet fully formed, babies cannot focus their eyes, quickly respond to stimuli, fully process the information received in order to perceive the color, size, shape, distance of objects.

Newborn children perceive the world upside down and in black and white, since the formation of their visual analyzer is not yet fully completed.

By the age of 1, the child's vision becomes almost as sharp as that of an adult, which can be checked using special tables. But the complete completion of the formation of the visual analyzer occurs only by 10-11 years. Up to 60 years on average, subject to the hygiene of the organs of vision and the prevention of pathologies, visual apparatus works properly. Then the weakening of functions begins, which is due to the natural wear and tear of muscle fibers, blood vessels and nerve endings.

We can get a three-dimensional image due to the fact that we have two eyes. It has already been said above that the right eye transmits the wave to the left hemisphere, and the left, on the contrary, to the right. Further, both waves are connected, sent to the necessary departments for decryption. At the same time, each eye sees its own "picture", and only with the right comparison they give a clear and bright image. If at any of the stages there is a failure, there is a violation of binocular vision. A person sees two pictures at once, and they are different.

A failure at any stage of the transmission and processing of information in the visual analyzer leads to various visual impairments.

The visual analyzer is not in vain compared with a TV. The image of objects, after they undergo refraction on the retina, enters the brain in an inverted form. And only in the relevant departments is it transformed into a form more convenient for human perception, that is, it returns “from head to foot”.

There is a version that newborn children see this way - upside down. Unfortunately, they cannot tell about it themselves, and it is still impossible to test the theory with the help of special equipment. Most likely, they perceive visual stimuli in the same way as adults, but since the visual analyzer is not yet fully formed, the information received is not processed and is fully adapted for perception. The kid simply can not cope with such volumetric loads.

Thus, the structure of the eye is complex, but thoughtful and almost perfect. First, light enters the peripheral part of the eyeball, passes through the pupil to the retina, is refracted in the lens, then is converted into an electrical wave and passes through the crossed nerve fibers to the cerebral cortex. Here, the received information is decoded and evaluated, and then it is decoded into a visual picture understandable for our perception. This is really similar to the antenna, cable and TV. But it is much more filigree, more logical and more surprising, because nature itself created it, and this complex process actually means what we call vision.

Visual sensations are obtained by exposing the eye to light rays. Light sensitivity is inherent in all living things. It manifests itself in bacteria and protozoa, reaching perfection in human vision. There is a structural similarity between the outer segment of the photoreceptor, as a complex membrane formation, with chloroplasts or mitochondria, that is, with structures in which complex bioenergetic processes take place. But unlike photosynthesis, where energy is accumulated, in photoreception, a quantum of light is spent only on “pulling the trigger”.

Light- change in the electromagnetic state of the environment. Absorbed by the visual pigment molecule, it triggers an as yet unknown chain of photoenzymochemical processes in the photoreceptor cell, which ultimately leads to the emergence and transmission of a signal to the next retinal neuron. And we know that the retina has three neurons: 1) rods and cones, 2) bipolar and 3) ganglion cells.

There are 7-8 million cones and 130-160 million rods in the retina. Rods and cones are highly differentiated cells. They consist of an outer and an inner segment, which are connected by a stem. The outer segment of the rods contains the visual pigment rhodopsin, and the cones contain iodopsin and represent a pile of superimposed discs surrounded by an outer membrane. Each disk is formed by two membranes, consisting of a biomolecular layer of lipid molecules, "inserted" between layers of protein. Inner segment has densely packed mitochondria. The outer segment and part of the inner are in contact with the digital processes of the pigment epithelium cells. In the outer segment, photophysical, photochemical and enzymatic processes of transformation of light energy into physiological excitation take place.

What scheme of photoreception is currently known? Under the action of light, the photosensitive pigment changes. And the visual pigment is complex colored proteins. The part that absorbs light is called the chromophore, retinal (vitamin A aldehyde). Retinal is bound to a protein called opsin. The retinal molecule has a different configuration, called cis- and trans-isomers. There are 5 isomers in total, but only the 11-cis isomer is involved in photoreception in isolation. As a result of the absorption of a light quantum, the curved chromophore straightens and the connection between it and the opsin is broken (before that, they were firmly connected). At the last stage, the transretinal is completely detached from the opsin. Along with decomposition, synthesis occurs, i.e., free opsin combines with retinal, but with 11-cisretinal. Opsin is formed as a result of fading of the visual pigment. Trans-retinal is reduced by the enzyme retinin reductase to vitamin A, which is converted to the aldehyde form, i.e. into retinal. In the pigment epithelium there is a special enzyme - retinisomerase, which ensures the transition of the chromophore molecule from trans to 11-cis isomeric form. But only the 11-cis isomer is suitable for opsin.

All visual pigments of vertebrates and invertebrates are built according to the general plan: 11 cis-retinal + opsin. But before light can be absorbed by the retina and cause a visual response, it must pass through all the media of the eye, where different absorption depending on the wavelength can distort the spectral composition of the light stimulus. Almost all the energy of light with a wavelength of more than 1400 nm is absorbed by the optical media of the eye, converted into thermal energy and, thus, does not reach the retina. In some cases, it can even cause damage to the cornea and lens. Therefore, persons of certain professions for protection from infrared radiation it is necessary to wear special glasses (for example, foundry workers). At a wavelength of less than 500 nm, electromagnetic energy can freely pass through aqueous media, but absorption will still occur here. The cornea and lens do not allow rays with a wavelength of less than 300 nm to pass into the eye. Therefore, safety goggles should be worn when working with sources of ultraviolet (UV) radiation (eg arc welding).

This allows, mainly for didactic purposes, to distinguish five main visual functions. In the process of phylogeny, visual functions developed in the following order: light perception, peripheral, central vision, color perception, binocular vision.

visual function- is extremely wide in range both in terms of diversity and in terms of the quantitative expression of each of its varieties. Allocate: absolute, distinctive, contrast, light sensitivity; central, peripheral, color, binocular depth, day, twilight and night vision, as well as near and far vision. In addition, vision can be foveal, parafoveal - eccentric and peripheral, depending on which part of the retina is exposed to light irritation. But simple light sensitivity is mandatory component any kind of visual function. Without it, no visual sensation is possible. It is measured by the light threshold, i.e. the minimum strength of the stimulus capable of causing light sensations under a certain state of the visual analyzer.

Light perception(light sensitivity of the eye) is the ability of the eye to perceive light energy and light of different brightness.

Light perception reflects the functional state of the visual analyzer and is characterized by the possibility of orientation in low light conditions.

The light sensitivity of the eye is manifested in the form of: absolute light sensitivity; distinctive light sensitivity.

Absolute Light Sensitivity- this is the absolute threshold of light energy (the threshold of irritation that can cause visual sensations; this threshold is negligible and corresponds to 7-10 quanta of light).

The discriminative light sensitivity of the eye (i.e., the difference in the minimum difference in illumination) is also extremely high. The range of light perception of the eyes surpasses all measuring instruments known in the art.

At various levels illumination, the functional abilities of the retina are not the same, since either cones or rods function, which provides a certain type of vision.

Depending on the illumination, it is customary to distinguish three types of visual function: daytime vision (photopic - at high light intensities); twilight (mesopic - at low and very low illumination); night (scotopic - at minimum illumination).

day vision- characterized by high sharpness and full color perception.

Twilight- low sharpness and color blindness. With night vision, it comes down to light perception.

More than 100 years ago, the anatomist Max Schultz (1866) formulated the dual theory of vision that daytime vision is carried out by cone apparatus, and twilight vision by rods, on the basis that the retina of diurnal animals consists mainly of cones, and nocturnal - of rods.

In the retina of a chicken (day bird) - mainly cones, in the retina of an owl (night bird) - sticks. Deep sea fish lack cones, while pike, perch, and trout have many cones. In fish with water-air vision (jumper fish), the lower part of the retina contains only cones, the upper part contains rods.

Later, Purkinje and Chris, independently of each other, unaware of Schulz's work, came to the same conclusion.

It has now been proven that cones are involved in the act of seeing in low light, and a special kind of rods are involved in the implementation of the perception of blue light. The eye has to constantly adapt to change. external environment, i.e. change your light sensitivity. The device is more sensitive than it reacts to a smaller impact. Light sensitivity is high if the eye sees very weak light, and low if relatively strong. To cause a change in the visual centers, it is necessary that photochemical processes occur in the retina. If the concentration of the photosensitive substance in the retina is greater, then the photochemical processes will be more intense. As the eye is exposed to light, the supply of photosensitive substances decreases. When going into darkness, the reverse process occurs. A change in the sensitivity of the eye during light stimulation is called light adaptation, a change in sensitivity as you stay in the dark is called dark adaptation.

The study of dark adaptation was initiated by Aubert (1865). The study of dark adaptation is carried out by adaptometers based on the Purkinje phenomenon. The Purkinje phenomenon consists in the fact that under conditions of twilight vision, the maximum brightness in the spectrum moves in the direction from red to blue-violet. It is necessary to find the minimum intensity that causes the sensation of light in the person being tested under the given conditions.

Light sensitivity is highly variable. The increase in light sensitivity is continuous, first rapidly (20 minutes), then more slowly and reaches a maximum after 40-45 minutes. Practically after 60-70 minutes of the patient's stay in the dark, the light sensitivity is set at a more or less constant level.

There are two main types of violations of absolute light sensitivity and visual adaptation: hypofunction of the cone apparatus of the retina, or day blindness, and hypofunction of the rod apparatus of the retina, or night blindness - hemeralopia (Shamshinova A.M., Volkov V.V., 1999).

Day blindness is characteristic of cone dysfunction. Its symptoms are an uncorrectable decrease in visual acuity, a decrease in photosensitivity, or a violation of adaptation from darkness to light, that is, light adaptation, a violation of color perception in various variations, improved vision at dusk and at night.

Characteristic symptoms are nystagmus and photophobia, blinding and changes in the cone macular ERG, a higher than normal rate of recovery of light sensitivity in the dark. Among the hereditary forms of cone dysfunction, or dystrophy, there are congenital forms (achromatopsia), blue cone monochromatism. Changes in the macular region are due to atrophic or degenerative changes. A characteristic feature is congenital nystagmus.

Changes in light and color perception are also observed in acquired pathological processes in the macular region, caused by toxic maculopathies caused by prolonged use of chloroquine (hydroxychloroquine, delagil), phenothiazine neuroleptics.

With hypofunction of the rod apparatus (hemeralopia), a progressive form due to a mutation of rhodopsin and a congenital stationary form are distinguished. Progressive forms include retinitis pigmentosa, cone-rod dystrophy, Usher syndrome, M. Bidl, Leber, and others, fundus punctata albescenc.

TO stationary relate:

1) stationary night blindness with normal fundus, in which there are no scotopic ERG, negative ERG and negative ERG complete and incomplete. The form of stationary night blindness, linked to sex (type II), is combined with severe and moderate myopia;

2) stationary night blindness with a normal fundus:

A) disease "Ogushi";

B) the Mizuo phenomenon;

B) plick retina of Kandory.

This classification is based on changes in the ERG, which reflects the function of the cone and rod apparatus of the retina.

Congenital stationary night blindness with pathological changes in the fundus, disease "Ogushi", is characterized by a kind of gray-white discoloration of the retina in the posterior pole and the equatorial zone, while the macular region is dark in contrast with the surrounding background. A variation of this form is the well-known Mizuo phenomenon, which is expressed in the fact that after a long adaptation, the unusual color of the fundus disappears, and the fundus looks normal. After exposure to light, it slowly returns to its original metallic color.

A large group is made up of various kinds non-hereditary hemeralopia, caused by general metabolic disorders (with vitamin A deficiency, with chronic alcoholism, diseases gastrointestinal tract, hypoxia and initial siderosis).

One of the early signs of many acquired diseases of the fundus may be impaired vision in low light conditions. At the same time, light perception is often disturbed by a mixed cone-rod type, as happens with retinal detachment of any genesis.

With any pathology of the visual-nerve pathway, accompanied by a disturbance in the visual field, the probability of a decrease in dark adaptation in its functioning part is the higher, the more distally the main disturbances are localized.

Thus, adaptation is disturbed in myopic disease, glaucoma, and even in tractus hemianopia, while in amblyopia of a central nature and cortical hemianopsia, adaptation disorders are usually not detected. Violations of light perception may not be associated with the pathology of the visual-nerve path. In particular, the photosensitivity threshold increases when light is restricted from entering the eye in cases of severe miosis or clouding of the optical media. A special form of retinal adaptation disorder is erythropsia.

In aphakia, when the retina is exposed to bright light without lens filtering of short-wavelength rays, the pigment of the "blue" and "green" cones fades, the sensitivity of the cones to red increases, and the red-sensitive cones respond with a superreaction. Erythropsia may persist for several hours after high-intensity exposure.

The light-receiving elements of the retina - rods and cones - are distributed in various departments unequally. The fovea centralis contains only cones. In the parafoveal region, a small number of rods join them. IN peripheral departments the retinal neuroepithelium consists almost exclusively of rods, the number of cones is small. The area of ​​the macula, especially the fovea centralis, has the most perfect, so-called central shaped vision. The central fossa is arranged in a peculiar way. There are more direct connections from each cone to the bipolar and ganglion cells than at the periphery. In addition, the cones in this area are much more closely packed, have a more elongated shape, bipolar and ganglion cells are displaced to the edges of the fovea. Ganglion cells that collect information from this area have very small receptive fields. Therefore, the fovea is the region of maximum visual acuity. The vision of the peripheral parts of the retina in relation to distinguish between small objects is significantly inferior to the central one. Already at a distance of 10 degrees from the fovea centralis, visual acuity is 5 times less, and further to the periphery it weakens even more. The main measure of visual function is the central visual acuity.

central vision is the ability of the eye to distinguish the details and shape of objects. It is characterized by visual acuity.

Visual acuity- this is the ability of the eye to perceive separately two bright points on a dark background, located at a minimum distance from each other. For a clear and separate perception of two luminous points, it is necessary that the distance between their images on the retina be no less than a known value. And the size of the image on the retina depends on the angle at which the object is seen.

Visual acuity measured in angular units. The angle of view is measured in minutes. Visual acuity is inversely related to the angle of view. The larger the angle of view, the lower the visual acuity, and vice versa. When examining visual acuity, the minimum angle at which two light stimuli of the retina can be perceived separately is determined. This angle on the retina corresponds to a linear value of 0.004 mm, equal to the diameter of one cone. The visual acuity of an eye that can perceive two points separately at an angle of 1 minute is considered normal visual acuity equal to 1.0. But vision can be higher - this is the norm. And it depends on the anatomical structure of the cones.

The distribution of light energy on the retina is influenced by: diffraction (with a narrow pupil less than 2 mm), aberration - a shift in the foci of rays passing through the peripheral sections of the cornea and lens, due to differences in the refractive power of these sections (relative to the central region) - this is a spherical aberration.

Geometric aberrations(spherical, astigmatism, distortion, coma) are especially noticeable with a pupil of more than 5 mm, since in this case the proportion of rays entering through the periphery of the cornea and lens increases.

Chromatic aberration, due to differences in the strength of refraction and the location of the foci of rays of different wavelengths, depends to a lesser extent on the width of the pupil.

Light scattering- part of the light is scattered in the microstructures of the optical media of the eye. With age, the severity of this phenomenon increases and this can cause glare from bright lights of the eye. Absorption, which has already been mentioned, also matters.

It also contributes to the visual perception of the smallest structure of the surrounding space, the hexagonal structure of the retinal receptive fields, of which many are formed.

For visual recognition, an important role is played by a system of filters of various spatial frequencies, orientations, and shapes. They function at the level of retinal ganglion cells, lateral geniculate bodies, and in the visual cortex. Spatial differentiation is closely dependent on light. Visual acuity, in addition to the function of light perception, is affected by adaptation to a long exposure of the object. For normal visual perception of the surrounding world, not only high visual acuity is necessary, but also full-fledged spatial and frequency channels of contrast sensitivity, which provide filtering of high frequencies that inform about small, low details of an object, without which it is impossible to perceive a holistic image, even with the distinguishability of small details and medium, especially sensitive to contrasts and creating prerequisites for high-quality high-frequency analysis of the contours of objects.

Contrast sensitivity- this is the ability to capture minimal differences in the illumination of two neighboring areas, as well as differentiate them by brightness. Completeness of information in the entire range of spatial frequencies is provided by visocontrastometry (Shamshinova A.M., Volkov V.V., 1999). To test distance visual acuity, Sivtsev and Snellen tables are widely used, which are evenly illuminated from the front (70 watts).

The best test remains the test in the form of Landolt rings. The Snellen tables, which we use, were approved at the second international congress in Paris in 1862. Later, many new tables appeared with various modifications and additions. An undoubted step forward to clarify the study of visual acuity was the Manoyer metric tables published at the turn of the two centuries.

In Russia, the tables of Golovin S.S. are generally recognized. and Sivtseva D.A., built according to the Manoyer system.

Distance visual acuity studies are carried out from a distance of 5 m, abroad more often from a distance of 6 m, with visual acuity that does not allow seeing the largest signs of the tables, they resort to showing single characters or the doctor's fingers on a dark background. If the patient counts fingers from a distance of 0.5 m, then visual acuity is designated as 0.01, if from 1 m - 0.02, etc. These calculations are carried out according to the Snellen formula vis \u003d d / D, where d is the distance from which the patient counts fingers or reads the first row of the table; D is the first row of the table, which the subject should normally see. If the patient cannot count the fingers located near the face itself, then the doctor's hand is moved in front of the eye to find out if the patient can determine the direction of the doctor's hand moving in front of the eye.

If the result is positive, then vision is designated as 0.001.

If the patient, when directing the ophthalmoscope mirror, feels the light from all sides correctly, then vision is designated as the correct projection of light.

If the patient does not feel light, then his vision is 0 (zero). High distance visual acuity can be without high near visual acuity and vice versa. For a more detailed assessment of changes in visual acuity, tables with a reduced “step” between rows are proposed (Rosenblum Yu.Z., 1961).

decline central vision only in the distance, corrected by glasses, it happens with ametropia, and near - due to a violation of accommodation during age-related changes. Decreased central distance vision with simultaneous improvement near it is associated with myopization due to swelling of the lens.

A decrease that cannot be eliminated by optical means, in the presence of hypermetropia, astigmatism, strabismus, on the worse seeing eye, speaks of amblyopia. If pathological processes in the macular region are detected, central vision decreases. In patients complaining of a central scotoma and a violation of color perception, as well as a decrease in contrast sensitivity in one eye, neuritis or retrobulbar neuritis should be excluded, if these changes are detected in both eyes, then it is necessary to exclude optochiasmal arachnoiditis or manifestations of a complicated congestive disc.

A persistent decrease in central and peripheral vision with a weakening of the reflex from the fundus of the eye may be the result of a violation of the transparency of the refractive media of the eye.

With normal visual acuity, a decrease in contrast sensitivity with disturbances in the paracentral region of the visual field is the initial manifestation of glaucoma.

Changes in the spatial contrast sensitivity (SCS) of the visual analyzer, which determines the minimum contrast required to detect an image of various sizes, can be the first sign of a disease in many pathological conditions visual system. To clarify the lesion, the study is supplemented by other methods. Modern computer game programs for the study of PCCh allow you to determine it in children.

Visual acuity is influenced by various side stimuli: auditory, the state of the central nervous system, locomotor apparatus eyes, age, pupil width, fatigue, etc.

peripheral vision If we fix any object, then in addition to a clear vision of this object, the image of which is obtained in the central part of the yellow spot of the retina, we also notice other objects that are at different distances (to the right, left, above or below) from the fixed object. It should be noted that the images of these objects projected onto the periphery of the retina are recognized worse than those of a fixed object, and the worse they are, the farther they are from it.

The acuity of peripheral vision is many times less than the central one. This is due to the fact that the number of cones towards the peripheral parts of the retina is significantly reduced. The optical elements of the retina in its peripheral sections are represented mainly by rods, which are in large numbers (up to 100 rods or more) connected to one bipolar cell, so the excitations coming from them are less differentiated and the images are less clear. However, peripheral vision in the life of the body plays no less a role than the central one. Academician Averbakh M.I. colorfully described the difference between central vision and peripheral vision in his book: “I remember two patients, lawyers by profession. One of them suffered from atrophy of the optic nerve in both eyes, with a central vision of 0.04-0.05, and almost normal visual field boundaries. Another was ill with retinitis pigmentosa, having normal central vision (1.0), and the field of vision was sharply narrowed - almost to the point of fixation. Both of them came to the courthouse, which had a long dark corridor. The first of them, not being able to read a single paper, ran completely freely along the corridor, without bumping into anyone and without needing outside help; the second, helplessly, stopped, waiting until someone took him by the arm and led him through the corridor to the bright meeting room. Misfortune brought them together, and they helped each other. Atrofik saw off his comrade, and he read the newspaper to him.

Peripheral vision is the space that the eye perceives in a stationary (fixed) state.

Peripheral vision expands our horizons, necessary for self-preservation and practical activities, serves to orient ourselves in space, and makes it possible to move freely in it. Peripheral vision, more than central, is susceptible to intermittent stimuli, including impressions of any movement; thanks to this, you can quickly notice people and vehicles moving from the side.

The peripheral parts of the retina, represented by rods, are especially sensitive to weak light, which plays an important role in low light conditions, when the ability to navigate in space, rather than the need for central vision, comes to the fore. The entire retina, which contains photoreceptors (rods and cones), is involved in peripheral vision, which is characterized by a field of vision. The most successful definition of this concept was given by I. A. Bogoslovsky: “The entire field that the eye simultaneously sees, fixing a certain point in space with a fixed gaze and with a fixed position of the head, constitutes its field of vision.” The dimensions of the visual field of a normal eye have certain boundaries and are determined by the boundary of the optically active part of the retina, located before the dentate line.

To study the visual field, there are certain objective and subjective methods, including: campimetry; control method; normal perimetry; static quantitative perimetry, in which the test object is not moved and does not change in size, but is presented at points of view with variable brightness at the points specified by a particular program; kinetic perimetry, in which the test object is displaced along the perimeter surface from the periphery to the center at a constant speed and the boundaries of the field of view are determined; color perimetry; flickering perimetry - the study of the field of view using a flickering object. The method consists in determining the critical frequency of flicker fusion in different areas retinas for white and colored objects of varying intensity. The critical flicker fusion frequency (CFFM) is the smallest number of light flickers at which the fusion phenomenon occurs. There are other methods of perimetry.

The simplest subjective method is the Donders control method, but it is only suitable for detecting gross visual field defects. The patient and the doctor sit opposite each other at a distance of 0.5 m, and the patient sits with his back to the light. When examining the right eye, the patient closes the left eye, and the doctor closes the right eye, while examining the left eye, vice versa. The patient is asked to look directly into the doctor's left eye with the open right eye. In this case, you can notice the slightest violation of fixation during the study. In the middle of the distance between himself and the patient, the doctor holds a stick with a white mark, a pen or a hand of his hand. By first placing the object outside his field of view and the field of view of the patient, the doctor gradually brings it closer towards the center. When the patient sees the object being moved, he must say yes. With a normal field of view, the patient should see the object at the same time as the doctor, provided that the doctor has normal visual field boundaries. This method allows you to get an idea of ​​​​the boundaries of the patient's field of view. With this method, the measurement of the boundaries of the field of view is carried out in eight meridians, which makes it possible to judge only gross violations of the boundaries of the field of view.

On the results of the study of the field of view big influence the size of the test objects used, their brightness and contrast with the background, therefore, these values ​​must be precisely known and, in order to obtain comparative results, must be kept constant not only during one study, but also during repeated perimetry. To determine the boundaries of the field of view, it is necessary to use white test objects with a diameter of 3 mm, and to study changes within these boundaries, test objects with a diameter of 1 mm. Colored test objects must have a diameter of 5 mm. With reduced vision, test objects of a larger size can be used. It is better to use round objects, although the shape of the object with the same area and brightness does not affect the results of the study. For color perimetry, test objects should be presented against a neutral gray background and be equally bright with the background and with each other. Pigment objects of various diameters, made of white and colored paper or nitro enamel, must be matte. In the perimeters, self-luminous objects can also be used in the form of a light bulb placed in a housing with a hole that is closed with colored or neutral light filters and diaphragms. Self-luminous objects are convenient to use when examining persons with low vision, as they can provide greater brightness and contrast with the background. The speed of movement of the object should be approximately 2 cm per 1 second. The subject during the study should be in a comfortable position, with constant fixation of the gaze on the fixation point. During the entire time of the study, it is necessary to monitor the position of the eyes and gaze of the subject. The boundaries of the field of view are equal: up - 50, down - 70, inwards - 60, outwards - 90 degrees. The dimensions of the boundaries of the visual field are influenced by many factors, depending both on the patient himself (pupil width, degree of attention, fatigue, state of adaptation), and on the method of studying the visual field (the size and brightness of the object, the speed of the object, etc.), and also from the anatomical structure of the orbit, the shape of the nose, the width of the palpebral fissure, the presence of exophthalmos or enophthalmos.

The field of view is most accurately measured by the perimetry method. The boundaries of the visual field are examined for each eye separately: the eye that is not being examined is switched off from binocular vision by applying a non-pressure bandage to it.

Defects within the field of view are divided according to their mono- or binocularity (Shamshinov A.M., Volkov V.V., 1999).

monocular vision(Greek monos - one + lat. oculus - eye) - this is vision with one eye.

It does not allow to judge the spatial arrangement of objects, it gives an idea only about the height, width, shape of the object. When a part of the lower visual field is narrowed without a clear quadrant or hemianopic localization, with a complaint of a sensation of a veil from below and medially, weakening after bed rest, this is a fresh retinal detachment with a rupture in the upper outer or upper part of the fundus.

With a narrowing of the upper field of vision with a feeling of an overhanging veil, aggravated by physical activity, are fresh detachments or ruptures of the retina in the lower sections. Permanent fallout upper half field of vision occurs with old retinal detachments. Wedge-shaped constrictions in the upper or lower inner quadrant are observed in advanced or advanced glaucoma and may occur even with normal ophthalmic tone.

A cone-shaped narrowing of the visual field, the apex associated with the blind spot, and the expanding base extending to the periphery (Jensen's scotoma), occurs with juxtapapillary pathological foci. More often with chronic productive inflammation of the choroid. Loss of the entire upper or lower half of the visual field in one eye is characteristic of ischemic optic neuropathy.

binocular vision(lat. bin [i] - two each, pair + oculus - eye) - this is the ability of a person to see the surrounding objects with both eyes and at the same time receive a single visual perception.

It is characterized by deep, relief, spatial, stereoscopic vision.

When the lower halves of the visual field fall out with a clear horizontal line, it is typical for trauma, especially gunshot wounds of the skull with damage to both occipital lobes of the cerebral cortex in the area of ​​the wedge. When the homonymously right or homonymously left halves of the visual field fall out with a clear boundary along the vertical meridian, this is a lesion of the optic tract, opposite to the hemianopic defect. If the reaction of the pupil to very weak light persists during this prolapse, then the central neuron of one of the hemispheres is affected visual cortex. Loss in both eyes and the right and left halves of the visual field with the preservation of the island in the center of the visual field within 8-10 degrees in elderly people may be the result of extensive ischemia of both halves of the occipital cortex of atherosclerotic origin. Loss of homonymous (right and left, upper and lower quadrants) visual fields, with upper quadrant homonymous hemianopsia, is a sign of damage to the Graziolle bundle with a tumor or abscess in the corresponding temporal lobe. At the same time, pupillary reactions were not disturbed.

Heteronymous loss of either halves or quadrants of the visual field is characteristic of chiasmal pathology. Binasal hemianopsia is often associated with concentric narrowing of the visual field and central scotomas and is characteristic of optochiasmal arachnoiditis.

Bitemporal hemianopsia - if defects appear in the lower outer quadrants - these are subsellar meningiomas of the tubercle of the Turkish saddle, tumors of the third ventricle and aneurysms of this area.

If upper external defects progress, these are pituitary adenomas, aneurysms of the internal carotid artery and its branches.

Peripheral visual field defect, mono- and binocular, may be the result of pressure on the optic nerve in the orbit, bone canal or cranial cavity of a tumor, hematoma, bone fragments.

Thus, a pre- or postchiasmal process may begin, or optic nerve perineuritis may manifest itself, it may underlie changes in the visual field and cortical changes.

Repeated measurements of the field of view should be carried out under the same lighting conditions (Shamshinova A.V., Volkov V.V., 1999).

Objective methods for studying the visual field are:

1. Pupillomotor perimetry.

2. Perimetry according to the alpha rhythm stop reaction.

By the reaction of stopping the alpha rhythm, the true boundaries of the peripheral field of vision are judged, while by the reaction of the subject, the subjective boundaries are judged. Objective perimetry becomes important in expert cases.

There are photopic, mesopic and scotopic fields of view.

Photopic is the field of view in conditions of good brightness. Under such illumination, the function of the cones predominates, and the function of the rods is to some extent inhibited. In this case, those defects that are localized in the macular and paramacular areas are most clearly identified.

Mesopic- study of the field of view in conditions of low brightness after a small (4-5 min) twilight adaptation. Both cones and rods work in almost the same modes. The extent of the field of view obtained under these conditions is almost the same as the normal field of view; Defects are especially well detected both in the central part of the visual field and on the periphery.

scotopic- study of the visual field after 20-30 minutes of dark adaptation mainly provides information about the state of the rod apparatus.

Currently, color perimetry is a mandatory study mainly in three categories of diseases: diseases of the optic nerve, retinal detachment and choroiditis.

1. Color perimetry is important in a number of neurological diseases, to prove the initial stages of tuberculous atrophy of the optic nerve, in retrobulbar neuritis and other diseases of the optic nerve. In these diseases, early impairments in the ability to recognize red and green colors are observed.

2. Color perimetry is essential in assessing retinal detachment. This impairs the ability to recognize blue and yellow A.

3. With fresh lesions of the choroid and retina, an absolute central scotoma and a relative scotoma in the peripheral part of the visual field are detected. Availability of livestock on different colors is early diagnostic sign many serious diseases.

Changes in the visual field may manifest as scotomas.

scotoma- This is a limited defect in the field of view. Scotomas can be physiological and pathological, positive and negative, absolute and relative.

Positive scotoma- this is a scotoma that the patient himself feels, and a negative one is detected with the help of special methods research.

Absolute scotoma- depression of sensitivity to light and does not depend on the intensity of the incoming light.

Relative scotoma- invisible at low intensity stimuli and visible at higher intensity stimuli.

Physiological scotomas- this is a blind spot (projection of the optic nerve head) and angioscotomas (projection of retinal vessels).

Shamshinova A.M. and Volkov V.V. (1999) so characterize scotomas.

Central zone- monocular central positive scotoma, often with metamorphopsia, occurs with monocular edema, Fuchs' dystrophy, cysts, up to retinal rupture in the macula, hemorrhage, exudate, tumor, radiation burn, vascular membranes, etc. Positive scotoma with micropsia is characteristic of central serous choriopathy . Negative scotoma occurs with axial neuritis, trauma, and ischemia of the optic nerve. Binocular negative scotoma is detected either immediately in both eyes, or with a short time interval, which happens with optic-chiasmatic arachnoiditis.

blind spot zone- monocular: expansion of the blind spot more than 5 degrees in diameter, subjectively not noticed, occurs with congestive disc, drusen of the optic disc, with glaucoma.

Central zone and blind spot zone (centrocecal scotoma)

Monocular, relapsing scotoma (congenital "fossa" of the optic disc with serous retinal detachment).

Binocular: toxic, Leber and other forms of optic neuropathy.

Paracentral zone (along the circumference within 5-15 degrees from the fixation point).

Monocular: with glaucoma (Björum's scotoma), visual discomfort, decreased contrast sensitivity and dark adaptation are possible.

Paracentral lateral zones (homonymously right-sided, homonymously left-sided).

Binocular: makes it difficult to read.

Paracentral horizontal zones (upper or lower).

Monocular: when there is a feeling of "cutting off" the upper or lower part of the object in question (ischemic neuropathy).

Median zone (between the center and the periphery in the form of a ring, annular scotoma, in late stages diseases, the ring shrinks to the center up to 3-5 degrees).

Monocular: with advanced glaucoma, etc.

Binocular: with tapetoretinal dystrophy, drug-induced retinal dystrophy, etc. Usually accompanied by a decrease in dark adaptation. Islet scotomas (in different areas periphery of the visual field).

Monocular, rarely binocular, often go unnoticed. They occur with pathological chorioretinal foci comparable in diameter to the optic nerve head (hemorrhages, tumors, inflammatory foci).

An increase in livestock to different colors is an early diagnostic sign of many serious diseases, which makes it possible to suspect the disease on early stages. So, the presence of a green scotoma is a symptom of a tumor of the frontal lobe of the brain.

The presence of a purple or blue spot on a light background is a hypertensive scotoma.

"I see through the glass" - the so-called glass scotoma, indicates vasospasm as a manifestation of vegetative neurosis.

Atrial scotoma (ocular migraine) in the elderly is early sign brain tumors or hemorrhages. If the patient does not distinguish between red and green, this is a conductive scotoma, if yellow and blue, then the retina and vascular membranes of the eye are affected.

color perception- one of the most important components of the visual function, which allows you to perceive objects of the outside world in all the diversity of their chromatic coloring - this is color vision, which plays an important role in human life. It helps to better and more fully learn the outside world, has a significant impact on the psychophysical state of a person.

Different colors have a different effect on the pulse rate and respiration, on the mood, tone them up or depress them. No wonder Goethe wrote in his study of colors: “All living things strive for color ... Yellow color pleases the eye, expands the heart, invigorates the spirit and we immediately feel warm, Blue colour, on the contrary, presents everything in a sad light. The correct perception of colors is important in labor activity (in transport, in the chemical and textile industries, doctors when working in medical institution: surgeons, dermatologists, infectious disease specialists). Without the correct perception of colors, artists cannot work.

color perception- the ability of the organ of vision to distinguish colors, that is, to perceive light energy of various wavelengths from 350 to 800 nm.

Long-wave rays, acting on the human retina, cause a sensation of red color - 560 nm, short-wave rays - blue, have a maximum spectral sensitivity in the range - 430-468 nm, in green cones the absorption maximum is at 530 nm. Between them are the rest of the colors. At the same time, color perception is the result of the action of light on all three types of cones.

In 1666 at Cambridge, Newton observed "the famous phenomena of colors" with the help of prisms. The formation of different colors during the passage of light through a prism was known by that time, but this phenomenon was not explained correctly. He began his experiments by placing a prism in front of a hole in the shutter of a darkened room. Ray sunlight passed through a hole, then through a prism and fell on a sheet of white paper in the form of color bands - a spectrum. Newton was convinced that these colors were originally present in the original white light, and did not appear in the prism, as was believed at the time. To test this position, he brought together the colored rays produced by the prism using two different methods: first with a lens, then with two prisms. In both cases, a white color was obtained, the same as before decomposition by the prism. Based on this, Newton came to the conclusion that white is a complex mixture various kinds rays.

In 1672 he submitted to the Royal Society a work called The Theory of Colours, in which he reported the results of his experiments with prisms. Identified seven primary colors of the spectrum and for the first time explained the nature of color. Newton continued his experiments and after completing the work in 1692 he wrote a book, but during the fire all his notes and manuscripts were lost. Only in 1704 did his monumental work entitled "Optics" come out.

We now know that different colors are nothing but electromagnetic waves. different frequency. The eye is sensitive to light of different frequencies and perceives them as different colors. Each color should be regarded in terms of three features that characterize it:

- tone- depends on the wavelength, is the main quality of the color;

- saturation- density of tone, percentage the main tone and impurities to it; the more the main tone in the color, the more saturated it is;

- brightness- lightness of color, manifested by the degree of proximity to white - the degree of dilution with white.

A variety of colors can be obtained by mixing only the three primary colors - red, green and blue. These basic three colors for a person were first established by Lomonosov M.V. (1757) and then Thomas Young (1773-1829). Experiments of Lomonosov M.V. consisted in projecting onto the screen superimposed circles of light: red, green and blue. When superimposed, the colors were added: red and blue gave magenta, blue and green - cyan, red and green - yellow. When applying all three colors, white was obtained.

According to Jung (1802), the eye analyzes each color separately and transmits signals about it to the brain in three different types nerve fibers, but Jung's theory was rejected and forgotten for 50 years.

Helmholtz (1862) also experimented with mixing colors and eventually confirmed Jung's theory. Now the theory is called the Lomonosov-Jung-Helmholtz theory.

According to this theory, there are three types of color-sensing components in the visual analyzer that react differently to color with different wavelengths.

In 1964, two groups of American scientists - Marx, Dobell, McNicol in experiments on the retina of goldfish, monkeys and humans, and Brown and Wahl on the human retina - conducted virtuoso microspectrophotometric studies of single cone receptors and discovered three types of cones that absorb light in various parts spectrum.

In 1958 de Valois et al. conducted research on monkeys - macaques, which have the same mechanism of color vision as in humans. They proved that color perception is the result of the action of light on all three types of cones. Radiation of any wavelength excites all the cones of the retina, but in varying degrees. With the same stimulation of all three groups of cones, a sensation of white color occurs.

There are congenital and acquired color vision disorders. About 8% of men have congenital defects in color perception. In women, this pathology is much less common (about 0.5%). Acquired changes in color perception are observed in diseases of the retina, optic nerve, central nervous system and general diseases of the body.

In the classification of congenital disorders of color vision by Chris - Nagel, red is considered the first and denotes it "protos" (Greek - protos - first), then go green - "deuteros" (Greek deuteros - second) and blue - "tritos" (Greek iritos - third). A person with normal color perception is called a normal trichromat. Abnormal perception of one of the three colors is designated respectively as proto-, deutero- and tritanomaly.

Proto - deutero - and tritanomaly is divided into three types: type C - a slight decrease in color perception, type B - a deeper violation, and type A - on the verge of losing the perception of red and green.

Complete non-perception of one of the three colors makes a person dichromatic and is designated respectively as protanopia, deuteranopia or tritanopia (Greek an - a negative particle, ops, opos - vision, eye). People with such a pathology are called: protanopes, deuteranopes, tritanopes.

Lack of perception one of the primary colors, such as red, changes the perception of other colors, since they do not have a share of red in their composition. Extremely rare are monochromats and achromats who do not perceive colors and see everything in black and white. In completely normal trichromats, there is a kind of exhaustion of color vision, color asthenopia. This phenomenon is physiological, it simply indicates the insufficient stability of chromatic vision in individuals.

The nature of color vision is influenced by auditory, olfactory, gustatory and many other stimuli. Under the influence of these indirect stimuli, color perception may be inhibited in some cases and enhanced in others. Congenital disorders of color perception are usually not accompanied by other changes in the eye, and the owners of this anomaly learn about it by chance during a medical examination. Such an examination is mandatory for drivers of all types of transport, people working with moving mechanisms, and for a number of professions that require correct color discrimination.

The color vision disorders that we talked about are congenital in nature.

A person has 23 pairs of chromosomes, one of which carries information about sexual characteristics. Women have two identical sex chromosomes (XX), while men have unequal sex chromosomes (XY). The transmission of a color vision defect is determined by a gene located on the X chromosome. The defect does not appear if the other X chromosome contains the corresponding normal gene. Therefore, in women with one defective and one normal X chromosome, color vision will be normal, but it may be the transmitter of the defective chromosome. A man inherits the X chromosome from his mother, and a woman inherits one from her mother and one from her father.

More than a dozen tests currently exist to diagnose color vision defects. IN clinical practice we use polychromatic tables of Rabkin E.B., as well as anomaloscopes - devices based on the principle of achieving subjectively perceived equality of colors by metered composition of color mixtures.

Diagnostic tables are built on the principle of the equation of circles different color in brightness and saturation. With their help, geometric figures and numbers of "traps" are indicated, which are seen and read by color anomalies. At the same time, they do not notice the number or figure marked with circles of the same color. Therefore, this is the color that the subject does not perceive. During the study, the patient should sit with his back to the window. The doctor holds the table at the level of his eyes at a distance of 0.5-1.0 meters. Each table is exposed for 2 seconds. Only the most complex tables can be displayed longer.

A classic device designed to study congenital disorders of the perception of red-green colors is the Nagel anomaloscope (Shamshinova A.M., Volkov V.V., 1999). The anomaloscope allows diagnosing both protanopia and deuteranopia, as well as protanomaly and deuteranomaly. According to this principle, the anomaloscope Rabkina E.B.

Unlike congenital, acquired color vision defects can occur in only one eye. Therefore, if acquired changes in color perception are suspected, testing should be carried out only monocularly.

Color vision disorders can be one of the early symptoms of an acquired pathology. They are more often associated with the pathology of the macular area of ​​the retina, with pathological processes and more high level- in the optic nerve, visual cortex in connection with toxic effects, vascular disorders, inflammatory, dystrophic, demyelinating processes, etc.

The threshold tables created by Yustova et al. (1953) took a leading place in the differential diagnosis of acquired diseases of the visual pathways, in the diagnosis of initial disorders of the transparency of the lens, in which one of the most common symptoms identified by the tables was trita deficiency of the second degree. The tables can also be used in cloudy optical media, if the uniform vision is not lower than 0.03-0.04 (Shamshinova A.M., Volkov V.V., 1999). Prospects for improving the diagnosis of ophthalmic and neuro-ophthalmic pathology are opened by a new method developed by Shamshinova A.M. et al. (1985-1997) - color static campimetry.

The research program provides for the possibility of changing not only the wavelength and brightness of the stimulus and background, but also the magnitude of the stimulus depending on the topography of receptive fields in the retina, the equation for brightness, stimulus and background.

The method of color campimetry makes it possible to carry out "topographic" mapping of the light and color sensitivity of the visual analyzer in the initial diagnosis of diseases of various origins.

Currently, the world clinical practice recognizes the classification of acquired color vision disorders, developed by Verriest I. (1979), in which color disorders are divided into three types depending on the mechanisms of their occurrence: absorption, alteration and reduction.

1. Acquired progressive disturbances in the perception of red-green color from trichromasia to monochromasia. The anomaloscope reveals changes of varying severity from protanomaly to protanopia and achromatopsia. Violation of this type is characteristic of the pathology of the macular area of ​​the retina and indicates violations in the cone system. The outcome of alteration and scotopization is achromatopsia (scotopic).

2. Acquired red-green disorders are characterized by a progressive impairment of color tone discrimination from trichromasia to monochromasia and are accompanied by blue-yellow disorders. On the anomaloscope in the Rayleigh equation, the range of green is extended. At serious illness color vision takes the form of achromatopsia and may manifest as scotoma. Violations of this type are found in diseases of the optic nerve. The mechanism is reduction.

3. Acquired blue-yellow color vision disorders: in the early stages, patients confuse the colors purple, violet, blue and blue-green, with its progression, dichromatic color vision is observed with a neutral zone in the region of about 550 nm.

The mechanism of color vision impairment is reduction, absorption or alteration. Disorders of this type are characteristic of diseases of the choroid and retinal pigment epithelium, diseases of the retina and optic nerve, and are also found in brown cataracts.

Acquired disorders also include a kind of pathology of visual perception, which boils down to the vision of all objects painted in one color.

Erythropsia- the surrounding space and objects are painted red or pink. This happens with aphakia, with some blood diseases.

xanthopsia- staining of objects in yellow color (an early symptom of damage to the hepato-biliary system: (Botkin's disease, hepatitis), when taking quinacrine.

cyanopsia- staining in blue (more often after cataract extraction).

Chloropsia- staining green (a sign of drug poisoning, sometimes substance abuse).

Control questions:

1. Name the main visual functions according to the order of their development in phylogenesis.

2. Name the neuro-epithelial cells that provide visual functions, their number, location in the fundus.

3. What functions does the cone apparatus of the retina perform?

4. What functions does the rod apparatus of the retina perform?

5. What is the quality of central vision?

6. What formula is used to calculate visual acuity less than 0.1?

7. List the tables and devices that can be used to examine visual acuity subjectively.

8. Name the methods and devices that can be used to examine visual acuity objectively.

9. What pathological processes can lead to a decrease in visual acuity?

10. What are the average normal boundaries of the visual field for white, in adults, in children (according to the main meridians).

11. Name the main pathological changes in visual fields.

12. What diseases usually cause focal visual field defects - scotomas?

13. List the diseases in which there is a concentric narrowing of the visual fields?

14. At what level is the conduction of the visual pathway disturbed during development:

A) heteronymous hemianopsia?

B) homonymous hemianopsia?

15. What are the main groups of all the colors observed in nature?

16. On what grounds do chromatic colors differ from each other?

17. What are the main colors perceived by a person in a normal way.

18. Name the types of congenital color vision disorders.

19. List acquired color vision disorders.

20. What methods are used to study color perception in our country?

21. In what form does the light sensitivity of the eye manifest itself in a person?

22. What kind of vision (functional ability of the retina) is observed at different levels of illumination?

23. What neuroepithelial cells function at different levels of illumination?

24. What are the properties of day vision?

25. List the properties of twilight vision.

26. List the properties of night vision.

27. What is the time of adaptation of the eye to light and darkness.

28. List the types of dark adaptation disorders (types of hemeralopia).

29. What methods can be used to study light perception?

The visual analyzer consists of an eyeball, the structure of which is schematically shown in Fig. 1, pathways and visual cortex.

Actually, the eye is called a complex, elastic, almost spherical body - the eyeball. It is located in the eye socket, surrounded by the bones of the skull. Between the walls of the orbit and the eyeball there is a fatty pad.

The eye consists of two parts: the eyeball itself and auxiliary muscles, eyelids, lacrimal apparatus. As a physical device, the eye is similar to a camera - a dark chamber, in the front of which there is a hole (pupil) that passes light rays into it. All inner surface the chamber of the eyeball is lined with a retina, consisting of elements that perceive light rays and process their energy into the first irritation, which is transmitted further to the brain through the visual channel.

Eyeball

The shape of the eyeball is not quite the correct spherical shape. The eyeball has three shells: outer, middle and inner and the nucleus, that is, the lens, and the vitreous body - a gelatinous mass enclosed in a transparent shell.

The outer shell of the eye is built of dense connective tissue. This is the densest of all three shells, thanks to which the eyeball retains its shape.

The outer shell is mostly white, which is why it is called protein or sclera. Its anterior part is partly visible in the area of ​​the palpebral fissure, its central part is more convex. In its anterior section, it connects to the transparent cornea.

Together they form a horn-scleral capsule of the eye, which is the most dense and elastic outer part of the eye, performs a protective function, making up, as it were, the skeleton of the eye.

Cornea

The cornea of ​​the eye resembles watch glass. It has an anterior convex and posterior concave surface. The thickness of the cornea in the center is about 0.6, and on the periphery up to 1 mm. The cornea is the most refractive medium of the eye. It is, as it were, a window through which paths of light pass into the eye. There are no blood vessels in the cornea and it is powered by diffusion from vasculature located on the border between the cornea and the sclera.

IN surface layers The cornea contains numerous nerve endings, which is why it is the most sensitive part of the body. Even a light touch causes a reflex instant closing of the eyelids, which prevents foreign bodies from entering the cornea and protects it from cold and heat damage.

The middle shell is called the vascular, because it contains the bulk of the blood vessels that feed the tissues of the eye.

The composition of the choroid includes the iris with a hole (pupil) in the middle, which acts as a diaphragm in the path of rays entering the eye through the cornea.

Iris

The iris is the anterior, well-visible section of the vascular tract. It is a pigmented round plate located between the cornea and the lens.

There are two muscles in the iris: the muscle that constricts the pupil and the muscle that dilates the pupil. The iris has a spongy structure and contains pigment, depending on the amount and thickness of which the shells of the eye can be dark (black or brown) or light (gray or blue).

Retina

The inner lining of the eye, the retina, is the most important part of the eye. It has a very complex structure and consists of nerve cells in the eye. According to the anatomical structure, the retina consists of ten layers. It distinguishes between pigment, neurocellular, photoreceptor, etc.

The most important of them is the layer of visual cells, consisting of light-perceiving cells - rods and cones, which also carry out color perception. The number of rods in the human retina reaches 130 million, cones about 7 million. Rods are able to perceive even weak light stimuli and are organs of twilight vision, and cones are organs of daytime vision. They convert the physical energy of light rays entering the eye into a primary impulse, which is transmitted through the visual first path to the occipital lobe of the brain, where a visual image is formed.

In the center of the retina is the macula lutea, which provides the most subtle and differentiated vision. In the nasal half of the retina, approximately 4 mm from the macula, there is an exit site for the optic nerve, forming a disc 1.5 mm in diameter.

From the center of the optic disc, the vessels of the artery and eyelid emerge, which are divided into branches that are distributed over almost the entire retina. The cavity of the eye is filled with the lens and the vitreous body.

Optical part of the eye

The optical part of the eye is made up of light-refracting media: the cornea, the lens, and the vitreous body. Thanks to them, the light rays coming from the objects of the external world, after being refracted in them, give a clear image on the retina.

The lens is the most important optical medium. It is a biconvex lens, consisting of numerous cells layered on top of each other. It is located between the iris and the vitreous body. There are no vessels or nerves in the lens. Due to its elastic properties, the lens can change its shape and become either more or less convex, depending on whether an object is viewed at close or far distances. This process (accommodation) is carried out through a special system eye muscles connected with thin threads with a transparent bag in which the lens is enclosed. The contraction of these muscles causes a change in the curvature of the lens: it becomes more convex and refracts rays more strongly when viewing closely spaced objects, and when viewing distant objects, it becomes flatter, the rays are refracted weaker.

vitreous body

The vitreous body is a colorless gelatinous mass that occupies most of the cavity of the eye. It is located behind the lens and makes up 65% of the contents of the mass of the eye (4 g). The vitreous body is the supporting tissue of the eyeball. Due to the relative constancy of composition and shape, practical uniformity and transparency of the structure, elasticity and resilience, close contact with the ciliary body, lens and retina, the vitreous body provides free passage of light rays to the retina, passively participates in the act of accommodation. It creates favorable conditions for constancy of intraocular pressure and stable shape of the eyeball. In addition, it also performs a protective function, protects the inner membranes of the eye (retina, ciliary body, lens) from dislocation, especially in case of damage to the organs of vision.

Functions of the eye

The main function of the human visual analyzer is the perception of light and the transformation of rays from luminous and non-luminous objects into visual images. The central visuo-nervous apparatus (cones) provides daytime vision (visual acuity and color perception), and the peripheral visual-nerve apparatus provides night or twilight vision (light perception, dark adaptation).