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Optic nerve neurons. Structure and functions of the optic nerve

The optic nerve delivers nerve messages to the area of the brain responsible for processing and perceiving light information.

Initially, these signals are obtained on the retina of the eye by converting light pulses. The visual center itself is localized in the cortical structure of the brain, in its occipital lobe. The totality of all nerve fibers that make up a nerve exceeds one million. This is the very first section visual analyzer, from the chiasm to the sclera, its length is about thirty millimeters. The optic nerve is divided into several sections.

During intrauterine development, the optic nerve, just like the retina of the eye, is formed from the same structures as the brain. Thus, we can say that the optic nerve is a continuation of the brain, extended to the periphery, beyond the edge of the skull. This nerve is different from normal cranial nerves.

The beginning of the optic nerve is considered to be ganglion neurocytes of the retina; they are the main component of the optic nerve head, and it ends with the chiasm (the segment where the intersection of the nerves coming from the two eyes occurs). The S-shaped bend of the optic nerve does not allow it to be stretched and injured in the event of a sudden change in location eyeball.

Structure of the optic nerve

What functions are provided by the optic nerve?

The optic nerve is the most important part of the entire process of converting light information. Its first and most significant function is the delivery of visual messages from the retina to the areas of the brain responsible for vision. Even the smallest injuries to this area can have severe complications and consequences.

Ruptures of nerve fibers threaten vision loss. Many pathologies are caused by structural changes in this area. This can lead to impaired visual acuity, hallucinations, and disappearance of color fields.

Scheme of movement of the visual impulse

The photosensitive cells of the retina are cones and rods. The largest number of such cells is concentrated at the location macular spot. The signals received by the light-sensitive cells travel first to the bipolar and then to the retinal ganglion cells. The nerve endings of these cells form the optic nerve. The separate optic nerve at this interval includes fibers exclusively from its “own” eye.

At this interval, the optic nerve is formed by fibers from the outer, inner part of the retina, as well as fibers coming from the macula. These fibers represent the macular ligament of the optic nerve.

Having formed on the retina, through the axons of ganglion neurocytes, the impulse moves to the optic nerve head, which is also located on the retina. Subsequently, through the optic canal, each from its own edge enters the skull. After this, the optic nerves follow frontal regions brain, and then partially come together, forming a cross. This area of partial intersection of the optic nerves is called the chiasm. Only the fibers that come from the inner halves of the retina cross. The nerve fibers coming from the outer part of the retina do not cross. Some fibers of the macular bundle also form a decussation.

After crossing, the left and right visual pathways appear, which absorb nerve fibers from the two eyes: part of the uncrossed fibers coming from the “own” eye, and the remaining amount is made up of fibers from the second eye, which came to this side as a result of the cross. Therefore, each optic nerve after the chiasm has fibers from equal parts of the retina - right or left.

Next, the visual pathways move posteriorly and outward, bypassing the cerebral peduncle, reaching visual areas in the subcortex of the brain. Neurons and axons are concentrated in these centers, which then go to the deep parts of the parietal and temporal lobes, but they follow different roads. As a result, the visual fibers are sent to the occipital lobe, where they reach the visual analyzer. In this area, the optical image is analyzed and synthesized and what is seen is identified.

Optic nerve sheaths

The outside of the optic nerve is lined by three meninges. The initial segment of the optic nerve is formed immediately upon its exit from the sclera. Here the nerve immediately acquires a myelin sheath, which is preserved along its entire length. The diameter of the optic nerve grows from 3.7 mm to 4.7 mm, thanks to the presence of these three medulla layers:

soft;
arachnoid;
hard.

All these layers, on one side, are in close interaction with the sclera, and on the opposite side, with the structures of the brain and are their direct extrapolation.

The dura mater is the outermost covering of the optic nerve. It is combined with the sclera, is characterized by significant thickness and is formed from coarse collagen formations, with a small admixture of elastic ones. The outer part of the membrane is lined with endothelial cells. At the epicenter of the junction of the dura mater and the sclera there are many vessels and trunks of ciliary nerves that penetrate the sclera.

The trunk of the optic nerve itself is covered with a soft membrane, which is delimited from the nerve by only a thin glial gap. This layer is extremely tightly connected to the optic nerve. Between them, many connective tissue septa (septa) are identified, which divide the optic nerve into bundles. The septa go inside the nerve bundles, giving the optic nerve itself greater strength. Blood vessels flow through these septa to the optic nerve trunk; they do not go inside the nerve bundles, so the nutrition of individual nerve fibers is carried out through these glial septa.

The vessels of the pia mater are not perforated, as are those located in the optic nerve. Intercellular connections are distinguishable between neighboring endothelial cells. The soft shell does not represent a barrier to metabolites, despite the presence of intercellular contacts.

The arachnoid membrane is located between the hard and soft shell. It is represented by a thin layer of collagen tissue, which is covered with flat cells. Numerous trabeculae connect it to the soft shell, forming a network. Trabeculae are composed of collagen and mesothelial cells. The number of mesothelial layers varies, but usually there are two. If the trabecula carries blood vessel, then there are more such layers. The border of the arachnoid membrane is located at the cribriform scleral plate, and it smoothly connects to the sclera. This membrane divides the intervaginal space into subarachnoid and subdural. The subarachnoid cavity ends at the sclera and is filled with subarachnoid fluid.

Optic disc (OND)

The ONH is represented by the neural processes of retinal ganglion neurocytes. This is the junction of all the optical fibers of the retina. The thickness of the nerve fibers and the retina itself increases as it approaches this area, so the disc protrudes slightly deeper into the eye and resembles a papilla.

The ONZ is localized in the nasal region of the fundus of the eye and is a pulpless nerve substance (according to its characteristics tissue structure). It does not have medullary surface layers, and the optic fibers that form it lack a myelin sheath. In the center of the disc there is a funnel-shaped depression into which the central artery enters and the central retinal vein exits. This place is called excavation or vascular funnel.

Normal ophthalmological picture of optic disc

The optic disc has an elliptical or rounded shape, with a large vertical meridian.
The size of the optic disc can be varied and depends on the method of ophthalmological testing.
A pinkish or slightly reddish color is considered normal. In old age, a yellowish color may be present.
The optic disc nipple is thicker towards the nasal edge, which is why its nasal part is redder than the temporal part. Normally, the temporal part is always slightly paler. U myopic people The optic disc is generally paler and this is the norm.
The optic disc has clear edges, the temporal edge stands out more sharply.
The presence of scleral and choroidal rings is distinguished.
The optic disc is localized, as a rule, at the level of the retina.
physiological excavation must be present.
On the optic nerve itself, retinal vessels are distinguishable - central, cilioretinal and optociliary vessels.

Diseases caused by disorders of the optic nerve

Incorrect development of anatomy, inflammation, organic lesions and injury can become a serious pathology and lead to serious consequences, including blindness.

developmental anomalies of the optic disc.
neuritis - retrobulbar and intrabulbar.
inflammation of the optic nerve.
ischemic neuropathy.
optochiasmal arachnoiditis.
congestive optic disc.
toxic damage to the optic nerve.

What is the blood supply to the optic nerve?

The system of short posterior ciliary arteries supplies the frontal portion of the optic nerve. A. retinae centralis is responsible for the blood supply to the retinal part of the optic nerve head. Branches from the choroidal vessels feed the temporal portion of this layer. The peripapillary choroidal vessels supply blood and nutrients to the prelaminar region of the optic disc. And its laminar part receives nutrients and oxygen thanks to the terminal arterioles of the peripapillary choroid.

From the frontal segment of the optic nerve, blood flow is organized through the participation of the central retinal vein. In the prelaminar area of the optic disc deoxygenated blood, saturated carbon dioxide and decay products, flows into the peripapillary veins, which deliver it to the ophthalmic vorticose veins. Blood enters the posterior central vein from the intracanal part of the optic nerve. Upon completion of its exit from the optic nerve trunk, it passes into the cavernous sinus. In case of injuries to the bone canal, it is this vein that usually causes hemorrhages into the nerve tissue. The intracranial segment is fed by a branched vascular network formed by the internal carotid artery and the anterior cerebral artery, the ophthalmic artery and the anterior communicating artery are also involved.

Vision is one of the most significant functions human body. It is thanks to it that the brain receives the bulk of information about the world around us, and the leading role in this is played by the optic nerve, through which terabytes of information pass per day, from the retina to the cerebral cortex.

The optic nerve, or nervus opticus, is the second pair of cranial nerves that inextricably connects the brain and the eyeball. Like any organ in the body, it is also susceptible to various diseases, as a result of which vision is rapidly, and most often irretrievably lost, since nerve cells die and are practically not restored.

To understand the causes of diseases and treatment methods, it is necessary to know the structure of the optic nerve. Its average length in adults varies from 40 to 55 mm, the main part of the nerve is located inside the orbit - the bone formation in which the eye itself is located. The nerve is surrounded on all sides by parabulbar tissue - adipose tissue.

It has 4 parts:

Intraocular.
Orbital.
Canalicular.
Cranial.

Optic disc

The optic nerve begins in the fundus of the eye, in the form of the optic nerve disc (OND), which is formed by processes of retinal cells, and it ends in the chiasm - a kind of “crossroads” located above the pituitary gland inside the skull. Since the optic disc is formed by a cluster nerve cells, it protrudes slightly above the surface of the retina, which is why it is sometimes called the “papilla.”

The area of the optic disc is only 2-3 mm 2, and the diameter is about 2 mm. The disc is not located strictly in the center of the retina, but is slightly shifted to the nasal side, and therefore a physiological scotoma is formed on the retina - a blind spot. The optic disc is practically not protected. The nerve sheaths appear only when it passes through the sclera, that is, at the exit from the eyeball to the orbit. The blood supply to the optic disc is carried out by small processes of the ciliary arteries and is only segmental in nature. That is why, when blood circulation is impaired in this area, a sharp and often irreversible loss of vision occurs.

Optic nerve sheaths

As already mentioned, the optic nerve head itself does not have its own membranes. The optic nerve sheaths appear only in the intraorbital part, at the site where it exits the eye into the orbit.

They are represented by the following tissue formations:

Pia mater.
Arachnoid (arachnoid, or choroid) membrane.
Dura mater.

All membranes envelop the optic nerve layer by layer until it exits the orbit into the skull. Subsequently, the nerve itself, as well as the chiasm, are covered only by a soft membrane, and already inside the skull they are located in a special tank formed by the subarachnoid (choroidal) membrane.

Blood supply to the optic nerve

The intraocular and orbital part of the nerve have many vessels, but due to their small size (mainly capillaries), the blood supply remains good only under conditions of normal hemodynamics throughout the body.

The optic disc has a small number of small vessels - these are the posterior short ciliary arteries, which only provide this segmentally important part optic nerve with blood. The central retinal artery supplies blood to the deeper structures of the optic disc, but again, due to the low pressure gradient in it and its small caliber, blood stagnation, occlusion and various infectious diseases often occur.

The intraorbital part already has a better blood supply, which comes mainly from the vessels of the pia mater, as well as from the central artery of the optic nerve.

The cranial part of the optic nerve and the chiasm are also richly supplied with blood due to the vessels of the soft and subarachnoid membranes, into which blood enters from the branches of the internal carotid artery.

Functions of the optic nerve

There are not very many of them, but they all play a significant role in human life.

List of main functions of the optic nerve:

transmission of information from the retina to the cerebral cortex through various intermediate structures;
quick response to various external stimuli (light, noise, explosion, approaching car, etc.) and as a result - operational reflex defense in the form of closing the eyes, jumping, withdrawing hands, etc.;
reverse transmission of impulses from the cortical and subcortical structures of the brain to the retina.

The visual pathway, or the pattern of movement of the visual impulse

The anatomical structure of the visual pathway is complex.

It consists of two sequential sections:

Peripheral part . It is represented by rods and cones of the retina (1 neuron), then by bipolar cells of the retina (2 neuron), and only then by long cell processes (3 neuron). Together, these structures form the optic nerve, chiasm, and optic tract.
Central part of the visual pathway . The optic tracts end their path in the external geniculate body (which is the subcortical center of vision), the posterior part of the optic thalamus and the anterior quadrigeminal. Further, the processes of the ganglia form the optic radiation in the brain. A cluster of short axons of these cells, called Wernicke's area, from which long fibers extend, forming the sensory visual center - Brodmann's cortical area 17. This area of the cerebral cortex is the “director” of vision in the body.

Normal ophthalmic appearance of the optic disc

When examining the fundus of the eye using ophthalmoscopy, the doctor sees the following on the retina:

The optic disc is usually light pink in color, but with age, or with atherosclerosis, disc pallor is observed.
There are normally no inclusions on the optic disc. With age, small yellowish-gray disc drusen (deposits of cholesterol salts) sometimes appear.
The contours of the optic disc are clear. Blurred disc contours may indicate increased intracranial pressure and other pathologies.
The optic disc normally does not have pronounced protrusions or depressions; it is almost flat. Excavations are observed with, in the later stages of glaucoma and other diseases. Disc edema is observed during congestion both in the brain and in the retrobulbar tissue.
Retina in young and healthy people bright red, without various inclusions, adheres tightly over the entire area to the choroid.
Normally, there are no stripes of bright white or yellow color, as well as hemorrhages.

Symptoms of optic nerve damage

Diseases of the optic nerve are in most cases accompanied by the main symptoms:

Rapid and painless deterioration of vision.
Loss of visual fields - from minor to total scotomas.
The appearance of metamorphopsia - distorted perception of images, as well as incorrect perception of size and color.

Diseases and pathological changes of the optic nerve

All diseases of the optic nerve are usually divided by reason:

Vascular - anterior and posterior ischemic neuroopticopathy.
Traumatic . There can be any localization, but most often the nerve is damaged in the canalicular and cranial parts. In case of fractures of the skull bones, mainly the facial part, a fracture of the process of the sphenoid bone, in which the nerve passes, often occurs. With extensive hemorrhages in the brain (road accidents, hemorrhagic strokes, etc.), compression of the chiasm area may occur. Any damage to the optic nerve can result in blindness.
Inflammatory diseases of the optic nerve - bulbar and retrobulbar neuritis, opto-chiasmatic arachnoiditis, as well as papillitis. Symptoms of inflammation of the optic nerve are in many ways similar to other lesions of the optic tract - vision deteriorates quickly and painlessly, and fog appears in the eyes. During treatment retrobulbar neuritis happens very often full recovery vision.
Non-inflammatory diseases of the optic nerve . Frequent pathological phenomena in the practice of an ophthalmologist are represented by edema of various etiologies.
Oncological diseases . The most common tumor of the optic nerve is benign gliomas in children, which appear before the age of 10-12 years. Malignant tumors are rare and usually have a metastatic nature.
Congenital anomalies - increase in the size of the optic disc, optic nerve hypoplasia in children, coloboma and others.

Research methods for diseases of the optic nerve

For all neuro-ophthalmological diseases, diagnostic examinations include both general ophthalmological methods and special ones.

Common methods include:

visometry - the classic definition of visual acuity with and without correction;
perimetry is the most revealing examination method, allowing the doctor to determine the location of the lesion;
ophthalmoscopy - if the initial parts of the nerve are damaged, especially with ischemic opticopathy, pallor, disc excavation or swelling, its blanching or, conversely, injection is revealed.

Special diagnostic methods include:

Magnetic resonance imaging of the brain (to a lesser extent computed tomography and targeted radiography). It is an optimal study for traumatic, inflammatory, non-inflammatory (multiple sclerosis) and oncological causes of the disease (optic nerve glioma).
Fluorescein angiography of retinal vessels - the “gold standard” in many countries, which makes it possible to see in which area the cessation of blood circulation occurred, if anterior ischemic neuropathy of the optic nerve has occurred, to establish the localization of the blood clot, and to determine further prognosis for the restoration of vision.
HRT (Heidelberg retinal tomography) - an examination showing in great detail changes in the optic disc, which is very informative for glaucoma, diabetes, and optic nerve dystrophies.
Ultrasound of the orbit It is also widely used for damage to the intraocular and orbital nerves; it is very informative if a child has been diagnosed with optic nerve glioma.

Treatment of optic nerve diseases

Due to the variety of causes that cause damage to the optic nerve, treatment should be carried out only after an accurate diagnosis has been made. clinical diagnosis. Most often, treatment of such pathologies is carried out in specialized ophthalmological hospitals.

Ischemic optic neuropathy - Very serious illness, which should begin to be treated in the first 24 hours from the onset of the disease. More long absence therapy leads to a persistent and significant decrease in vision. For this disease, a course of corticosteroids, diuretics, angioprotectors, as well as drugs aimed at eliminating the cause of the disease are prescribed.

Traumatic pathology of the optic nerve at any part of its path can threaten serious visual impairment, therefore, first of all, it is necessary to eliminate compression on the nerve or chiasm, which is possible using the technique of forced diuresis, as well as performing trephination of the skull or orbit. The prognosis for such injuries is very ambiguous: vision may remain 100%, or may be completely absent.

Retrobulbar and bulbar neuritis are most often the first sign of multiple sclerosis (up to 50% of cases). The second most common cause is infection, both bacterial and viral (herpes virus, CMV, rubella, influenza, measles, etc.). Treatment is aimed at eliminating swelling and inflammation of the optic nerve using large doses corticosteroids, as well as antibacterial or antiviral drugs, depending on the etiology.

Benign neoplasms occur in 90% of children. Optic nerve glioma is located inside the optic canal, that is, under the membranes, and is characterized by proliferation. This pathology of the optic nerve cannot be treated, and the child may go blind.

Optic nerve glioma gives the following symptoms:

vision decreases very early and quickly, up to blindness on the affected side;
bulging eyes develop - non-pulsating exophthalmos of the eye, the nerve of which is affected by the tumor.

In most cases, optic nerve glioma affects the nerve fibers and, much less frequently, the optic-chiasmatic zone. The defeat of the latter usually significantly complicates the early diagnosis of the disease, which can lead to the spread of the tumor to both eyes. For early diagnosis It is possible to use MRI or Rese radiographs.

Optic nerve atrophy of any origin is usually treated with courses twice a year to maintain stability of the condition. Therapy includes both medications (Cortexin, B vitamins, Mexidol, Retinalamin) and physiotherapeutic procedures (electrical stimulation of the optic nerve, magnetic and electrophoresis with drugs).

If you detect changes in vision in yourself or in your relatives, especially in old age or childhood, you need to contact your treating ophthalmologist as soon as possible. Only a doctor can correctly diagnose and prescribe the necessary measures. Delay in treating diseases of the optic nerve threatens blindness, which cannot be cured.

More than 90% sensory information. Vision- a multi-link process that begins with the projection of an image onto the retina. Then photoreceptors, transmission and transformation of visual information occur in the neural layers of the visual system, and the visual ends with the decision about the visual image being made by the higher cortical parts of this system.

Accommodation called the adaptation of the eye to clearly seeing objects at different distances. The main role in accommodation is played by the lens, which changes its curvature and, consequently, its refractive power.

For a normal young person's eye, the farthest point of clear vision lies at infinity. The nearest point of clear vision is at a distance of 10 cm of the eye.

Presbyopia. The lens loses elasticity with age, and when the tension of the zonules of Zinn changes, its curvature changes little. Nearby objects are poorly visible.

Myopia. rays from a distant object will focus not on the retina, but in front of it, in the vitreous body.

Farsightedness. Rays from a distant object are focused not on the retina, but behind it.

Astigmatism. unequal refraction of rays in different directions (for example, along the horizontal and vertical meridian).

Eyeball has a spherical shape, which makes it easier to rotate to aim at the object in question. On the way to the light-sensitive membrane of the eye (retina), light rays pass through several transparent media - the cornea, lens and vitreous. A certain curvature and refractive index of the cornea and, to a lesser extent, the lens determine the refraction of light rays inside the eye.

Pupil called the hole in the center of the iris through which light rays pass into the eye. The pupil sharpens the image on the retina, increasing the depth of field of the eye.

If you cover your eye from the light and then open it, the pupil, which has dilated during darkening, quickly narrows (“ pupillary"). The muscles of the iris change the size of the pupil, regulating the amount of light entering the eye. The maximum change in the diameter of the pupil changes its area by approximately 17 times. When one eye is illuminated, the pupil of the other also narrows; this is called friendly.

Retina It is the inner light-sensitive layer of the eye.

There are two types of photoreceptors here (rods and cones: Cones function in high light conditions, they provide daytime and color vision; much more photosensitive rods are responsible for twilight vision) and several types of nerve cells. All of the listed retinas with their processes form the nervous apparatus of the eye, which not only transmits information to the visual centers of the brain, but also participates in its analysis and processing. Therefore, the retina is called the part of the brain located in the periphery.

The place where the optic nerve exits the eyeball, the optic disc, is called blind spot. It does not contain photoreceptors and is therefore insensitive to light. We do not feel the presence of a “hole” in the retina.

From the retina, visual information travels along the optic nerve fibers to the brain.

Visual adaptation. When moving from darkness to light, temporary blindness occurs, and then the sensitivity of the eye gradually decreases. This adaptation to bright light conditions is called light adaptation. The opposite phenomenon (dark adaptation) is observed when moving from a light room to an almost unlit room. At first, a person sees almost nothing due to reduced excitability of photoreceptors and visual neurons. Gradually, the contours of objects begin to emerge, and then their details also differ, as the sensitivity of photoreceptors and visual neurons in the dark gradually increases.

Blinding brightness of light. Light that is too bright causes an unpleasant feeling of being blinded. Upper limit blinding brightness depends on the adaptation of the eye: the longer the dark adaptation, the lower the brightness of the light causes blinding.

The role of eye movements for vision. When looking at any objects, the eyes move. Eye movements are carried out by 6 muscles attached to the eyeball. The movement of the two eyes occurs simultaneously and in a friendly manner. The important role of eye movements for vision is also determined by the fact that for the brain to continuously receive visual information, image movement on the retina is necessary. with motionless eyes and objects disappears after 1-2 s. To prevent this from happening, the eye, when examining any object, produces continuous jumps that are not felt by a person. As a result of each jump, the image on the retina shifts from one photoreceptor to a new one. The more complex the object in question, the more complex the trajectory of eye movement. They seem to trace the contours of the image, lingering on its most informative areas (for example, in the face - these are the eyes).

. When looking at any object, a person with normal vision does not have the sensation of two objects, although there are two images on two retinas. The images of all objects fall on the so-called corresponding, or corresponding, areas of the two retinas, and in human perception these two images merge into one.

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Description

Visual pathways- these are nerve fibers that conduct visual stimuli from the retina to the subcortical formations (primary visual centers) and further to the occipital lobe cortex (cortical visual centers). The visual pathway is divided into two parts: peripheral and central. The peripheral part includes

optic nerve (n. opticus),
optic chiasma (chiasma opticum)
and the optic tract (tractus opticus).

The central part of the visual pathway consists of

The visual pathway is part visual analyzer- a complex system of optical and oculomotor centers and their connections, ensuring the perception, analysis and integration of visual stimuli. Let us consider in more detail the components of the peripheral and central parts of the visual pathway.

Optic nerve

Optic nerve (n. opticus) - the second pair of cranial nerves, representing the initial section of the visual pathway. It is formed by the axons of visual ganglion neurocytes of the ganglion layer of the retina of the eyeball. In terms of development, the optic nerve, like the retina, is part of the brain, which makes it different from other cranial nerves.

The optic nerve begins in the area of the visual part of the retina (pars opticae retinae) with the disk, or nipple, of the optic nerve (discus n. optici), leaves the eyeball through the cribriform plate of the sclera, in the orbit it is directed back and medially, then passes through the bone visual channel(canalis opticus) into the cranial cavity. In the optic canal it is located superior and medial to the ophthalmic artery (a. ophthalmica). After leaving the optic canal at the base of the brain, both optic nerves form an incomplete optic chiasm (chiasma opticum) and pass into optic tracts(tractus opticus). Thus, the nerve fibers of the optic nerve continue continuously to the lateral geniculate body. The optic nerve has four divisions:

intraocular (intrabulbar) - from the beginning of the optic nerve to its exit from the eyeball;
orbital (retrobulbar) - from the point where the optic nerve exits the eyeball to the entrance to the optic canal;
intracanal - corresponds to the length of the optic canal;
intracranial (intracranial) - from the place of exit from the optic canal to the chiasm.

The total length of the optic nerve is 35-55 mm. The length of the intraocular segment is 0.5-1.5 mm, orbital - 25-35 mm, intracanal - 5-8 mm, intracranial - 4-17 mm (Tron E.Zh., 1955).

Optic disc - the junction of the optical fibers of the retina in the channel formed by the membranes of the eyeball. It is located in the nasal part of the fundus at a distance of 2.5-3 mm from the posterior pole of the eye and 0.5-1 mm downward from it. The shape of the disc is round or slightly oval, elongated in the vertical direction. Its diameter is 1.5-1.7 mm. In the center of the disk there is a depression (excavatio disci), which has the shape of a funnel (vascular funnel), less often a cauldron. In the area of this depression pass the central artery and central vein of the retina. The optic disc region does not contain photosensitive elements and is physiologically a blind spot. In the retina in the disc area, the nerve fibers do not have a myelin sheath. They acquire it when they leave the eyeball as part of the optic nerve. In the orbit, the optic nerve forms a helical bend, which prevents stretching of the nerve fibers during movements of the eyeball.

In the optic nerve, as well as throughout the entire visual pathway, there are four conductors associated with certain areas of the retina:

papillomacular bundle associated with the macula area;
crossed fibers connected to the nasal half of the retina;
uncrossed fibers going to the temporal half of the retina;
fibers of the temporal crescent connected to the extreme periphery of the nasal half of the retina.

As is known, the temporal half of the visual field of one eye corresponds to the nasal half of the visual field of the other eye. But the temporal half of the visual field is 30-40 degrees (along the horizontal meridian) larger than the nasal half. If you superimpose the visual field of the right and left eyes on each other so that the fixation points, vertical and horizontal meridians coincide, and so that the nasal half of the visual field of one eye covers the temporal half of the visual field of the other eye, then at the extreme periphery of the temporal halves of the visual field there will remain free a small semi-lunar-shaped area. It's called temporal crescent(Fig.2)

Fig.2. Temporal crescent of the visual field (according to Lauber). The area of the temporal crescent on both sides is shaded

and represents that part of the visual field that, during normal binocular vision, is always perceived monocularly.

Fibers originating from the outer parts of the retina form a straight (uncrossed) peripheral bundle. The fibers starting from the inner half of the retina, together with part of the fibers of the papillomacular bundle, move to the opposite side, forming the optic chiasm, and then connect with the uncrossed fibers of the opposite side, forming the optic tract.

Papillomacular bundle begins somewhat outward and downward from the center of the yellow spot of the retina (macula). It consists of optical fibers that partially intersect at the chiasm. In the papillomacular bundle there are also crossed and uncrossed fibers, associated with the nasal and temporal halves of the macula. Directly behind the eyeball, the papillomacular bundle occupies a peripheral position in the lower outer quadrant of the cross section of the optic nerve. Here it has the shape of a triangle, the apex of which is directed towards the central vessels, and the base is adjacent to the periphery of the cross section (Fig. 3).

Rice. 3. Diagram of the course of fibers in the optic nerve (according to Genshin): A - retina and optic nerve head; B - optic nerve directly behind the eye; C - optic nerve after the entrance of the central vessels; D - posterior part of the orbital segment; E - intracranial part

Further posteriorly, after the vessels exit the nerve, the papillomacular bundle is located in the center of its cross section. In the orbital and intracanal parts it has the shape of a vertical oval. The most complete picture of the progress separate groups Optic nerve fibers are given by the Henschen scheme, which takes into account the position of both the papillomacular bundle and crossed and uncrossed fibers (Fig. 3).

Near the eyeball, uncrossed fibers are presented in the form of two isolated bundles, which are separated from each other by the papillomacular bundle lying between them. In that part of the optic nerve where the papillomacular bundle occupies a central position, both bundles of uncrossed fibers merge with each other, forming one crescent-shaped bundle occupying a ventrolateral position. The crossed fibers along the entire length of the optic nerve are presented in the form of a single bundle located dorsomedially. The course of the temporal crescent fibers in the optic nerve is unknown. Experiments on monkeys have shown that fibers coming from the upper half of the retina lie in the upper half of the optic nerve, and fibers from the lower half of the retina lie in its lower half.

The fibers of the optic nerve differ not only in direction, but also in caliber: there are thin and thick fibers. It is assumed that thick fibers transmit light stimulation to the visual centers, while thin fibers are reflex and serve to transmit light stimulation to the accessory (parasympathetic) nucleus of the oculomotor nerve. In addition to centripetal fibers, the optic nerve also contains centrifugal fibers that go to the retina. They are believed to begin in the lamina tecti and end in the granular layer of the retina. The significance of these centrifugal fibers is not well understood.

The optic nerve in the orbit, optic canal and in the cranial cavity lies in the external and internal sheaths of the optic nerve, which in their structure correspond to the dura mater of the brain. The internal sheath limits the intervaginal space from the inside and consists of two sheaths: soft and cobwebby. The soft membrane directly covers the optic nerve trunk, separated from it only by a layer of neuroglia. Numerous septa (septa) extend from it into the optic nerve trunk, dividing the optic nerve into separate bundles of nerve fibers. The intervaginal space of the optic nerve is a continuation of the interthecal (subdural) space of the brain. It's full cerebrospinal fluid. Impaired fluid outflow from the intervaginal space of the optic nerve leads to papilledema.

Chiasma

Chiasma located at the base of the brain anterior to the gray tubercle above the area of the sella turcica. From above, the chiasm borders on the bottom of the third ventricle, from below - on the diaphragm of the sella turcica, which is a section of the dura mater covering the entrance to the sella turcica from above. On the sides the chiasm is surrounded by large vessels of the circle of Willis. The pituitary funnel (infundibulum) is adjacent to it at the back. The anterior edge of the chiasm in some cases adjoins the main bone in the area of the chiasmatic groove (sulcus chiasmaticus). The chiasma is covered with soft meninges, with the exception of its upper surface, where it is fused with the bottom of the third ventricle.

In the chiasm, all fibers from both optic nerves are grouped over a short distance and there is partial crossover of fibers. The fibers coming from the nasal halves of the retinas intersect, but the fibers from the temporal halves of the retinas do not intersect (do not pass to the opposite side). Both fibers associated with the periphery of the retina and fibers of the papillomacular bundles take part in this partial decussation. The course of the fibers in the chiasm is complex.

Crossed fibers are mainly grouped in the medial part of the chiasm, uncrossed fibers - in its lateral part. The course of crossed fibers is the most complex. The fibers coming from the inferior nasal quadrant of the retina in the lower part of the optic nerve pass to the other side near the anterior edge of the chiasma at its lower surface. Passing through the midline, these fibers enter the optic nerve of the opposite side. Here they form an arcuate bend, the so-called anterior knee of the chiasm, and then are directed into the optic tract. Fibers coming from the superior nasal quadrant of the retina pass to the other side at the posterior edge of the chiasm closer to its superior surface. Before the decussation, they enter the optic tract of the same side for some distance, forming an arched bend - the posterior knee of the chiasm, and then move to the other side.

Uncrossed fibers are located in the lateral parts of the chiasm. A bundle of these fibers is split into a number of thin layers, between which crossed fibers lie.

Part of the crossed fibers passing through the zone occupied by uncrossed fibers in the posterior half of the chiasma at its extreme lateral periphery is again collected into a continuous bundle. This continuous bundle of crossed fibers bordering the zone of uncrossed fibers contains the fibers of the temporal crescent.

The papillomacular bundle in the anterior part of the chiasm is located in the center of its lateral sections. In the posterior part of the chiasm, both papillomacular bundles come somewhat closer to each other and move closer to the upper surface. Partial decussation of the papillomacular bundles occurs in the posterior part of the chiasm under the bottom of the third ventricle. The course of the fibers in the chiasm is illustrated in Figures 4 and 5.

Fig.4. Diagram of the course of fibers in the chiasm (according to Kestenbaum): ts - fibers from the superior temporal quadrant of the retina; ti - fibers from the inferotemporal quadrant of the retina; ns - fibers from the superior nasal quadrant of the retina; ni - fibers from the inferior nasal quadrant of the retina; m - yellow spot of the right eye; hs - fibers from the upper left quadrant of the retina; hi - fibers from the lower left quadrant of the retina; ms+mi - fibers from the upper and lower left quadrants of the macula of both eyes

Rice. 5. Fiber path diagram (according to Tracker): I - optic nerves; II - optic tracts

Optic tract

Optic tracts start from the posterior surface of the chiasm and end at the external geniculate bodies. Their length is on average 4 - 5 cm. From the chiasm, the optic tracts go upward and backward, gradually moving away from each other. On this path, they first go around the gray tubercle, and then pass along the lower surface of the cerebral peduncles. Only a small anterior part of the optic tract lies freely at the base of the brain. The posterior part of the optic tract is covered by the temporal lobe.

In the optic tract, crossed fibers are located ventromedially, uncrossed fibers are located dorsolaterally. The papillomacular bundle occupies a central position. The vertical projection of the retina is preserved in the optic tract. This means that the fibers from the upper quadrants of the retina in the optic tract are located superiorly, and the fibers coming from the lower quadrants of the retina are located inferiorly.

The optic tract in its posterior part, bending around the cerebral peduncle, at its outer sections is divided into three roots, which end in the external geniculate body, the thalamic cushion and the anterior quadrigeminal tract (superior optic colliculus). Based on clinical, anatomical and experimental data, it has been established that in humans only the external geniculate body is the primary visual center. It is not the visual fibers that go to the quadrigeminal region, but the reflex fibers that ensure the reaction of the pupil to light.

External geniculate body

External geniculate body It is a small oblong elevation in the posterior part of the visual thalamus on the side of the pillow. At the ganglion cells of the lateral geniculate body, the fibers of the optic tract end and the fibers of the Graziole bundle originate. This is where the peripheral neuron ends and the central neuron of the visual pathway begins.

In the external geniculate body there is a certain projection of the retina (Fig. 6).

Fig.6. Projection of the retina on the external geniculate body (according to Brouwer and Zeman): 1 - upper half of the retina; 2 - lower half of the retina; 3 - upper half of the yellow spot; 4 - lower half of the yellow spot; 5 - upper half of the temporal crescent; 6 - lower half of the temporal crescent

Most of the external geniculate body is occupied by the projection of the retinal sections involved in the act of binocular vision. The extreme periphery of the nasal half of the retina, corresponding to the monocularly perceptive temporal crescent, is projected onto a narrow zone in the ventral part of the lateral geniculate body. The projection of the macula occupies a large area in the dorsal part. The superior quadrants of the retina project to the lateral geniculate body ventromedially, lower quadrants- ventrolateral. In addition, crossed and uncrossed fibers in the lateral geniculate body terminate at different layers of ganglion cells. Layers of ganglion cells located on top of each other lie between layers of white matter. In this case, layers of ganglion cells that end with crossed fibers alternate with layers that end with uncrossed fibers. Thus, both eyes have a separate representation in the external geniculate body.

Central neuron of the visual pathway

The primary visual centers are connected to the occipital lobe cortex centripetal and centrifugal fibers. The fibers of the central neuron of the optic pathway, after exiting the lateral geniculate body, pass through the internal capsule. They lie in her back thigh. From here, these fibers, as part of the Graziole bundle, are directed to the area of the calcarine sulcus of the occipital lobe cortex. On its way through the white matter of the brain Graziole bun goes around the lower and posterior horns lateral ventricle. The anterior section of the Graziole bundle is located in the temporal and parietal lobes, and its posterior section in the parietal and occipital lobes. The fibers of the central neuron of the optic pathway in the temporal lobe extend far anteriorly to the anterior end of the inferior horn of the lateral ventricle, forming Meyer's loop.

The central neuron of the visual pathway has vertical projection of the retina: the dorsal part of the Graziole bundle is connected to the upper quadrants of the retinas of both eyes, the ventral part is connected to the lower quadrants, middle part the Graziole bundle, located between its ventral and dorsal sections, is associated with the area of the macula. The fibers in the central neuron of the optic pathway are grouped so that the crossed and uncrossed fibers associated with the corresponding points in the retinas of both eyes are located nearby. Due to this, hemianopic visual field defects caused by damage to the Graziole bundle are characterized by great symmetry.

Cortical visual centers

Visual cortex cerebral hemispheres consists of the primary receptive field (area striata) - Brodmann's field 17 - and secondary (extrastriate) fields 18 and 19. The fibers of the central neuron of the visual pathway end in the area of the striatal field. This primary (projection) zone of the visual analyzer. It is located mainly on the medial surface of the occipital lobe in the region of the upper and lower lips of the calcarine groove (sulcus calcarinus), extending to the outer surface of the occipital lobe in the part where the end of the calcarine groove enters (Fig. 7).

Fig.7. Area striata (no Pfeiffer) on the medial surface (A) and at the posterior pole of the occipital lobe (B); area striata is shaded

The upper lip of the calcarine groove is made up of a wedge (cuneus), the lower lip is made up of a lingular gyrus (gyrus linqualis). The cortex of the occipital lobe in the region of the wedge, lingular gyrus and in the depths of the calcarine sulcus has a special structure and is called the striped area (area striata) - area 17 according to Brodmann.

The fibers of the central neuron of the optic pathway end in the striatal cortex at the cells of layer IV, but, as in the external geniculate body, crossed and uncrossed fibers end at different layers of ganglion cells. In the region of the striatal field, layer IV of ganglion cells breaks up into three layers located one above the other: IVa, IVb, IVc. Uncrossed fibers end in layer IVa cells, crossed fibers end in layer IVc ganglion cells. Thus, in the occipital lobe cortex, both eyes have a separate representation.

The visual analyzer is characterized by retinotopic projection, that is, the projection of certain points of the retina onto the corresponding parts of the visual pathway (Fig. 8).

Rice. 8. Areas of the retina in the “mosaic of nerve fibers” on various levels visual pathway on the right (combined according to Kestenbaum and Walsh): a - optic disc; b - optic nerve behind the entry point of the vessels; c - optic nerve near the chiasm; d - chiasma; e - visual tract; f - external geniculate body; g - Graziole bundle; h - regia calcarina on the medial surface of the occipital lobe (right, view from the medial surface); m - macula; ns - superior nasal quadrant of the retina; ni - inferior nasal quadrant of the retina; ts - superotemporal quadrant of the retina; ti - inferotemporal quadrant of the retina; rcs - upper half of the right temporal crescent; rci - lower half of the right temporal crescent; ms - upper right quadrants of the macula of both eyes; mi - lower right quadrants of the macula of both eyes; hs and hi - upper and lower right quadrants of the retina of both eyes; lcs and lci - upper and lower half left temporal crescent

In the area of the striped field there is both a vertical and horizontal projection of the retina (Fig. 9).

Fig.9. Projection of the retina onto the occipital lobe cortex (according to Holmes)

The vertical projection of the retina in the occipital lobe cortex is ensured by the fact that the upper lip of the calcarine sulcus is connected to the upper quadrants of the retina, and underlip- with lower quadrants. The horizontal projection is characterized by the fact that the projections of the macula, peripheral parts of the retina and the region of the temporal crescent occupy a certain position in the occipital lobe cortex. The projection of the macula is located in the region of the pole of the occipital lobe. The peripheral parts of the retina are projected onto the anterior part of the striatal field. The projection of the area of the temporal crescent is located in the most anterior parts of the calcarine sulcus, immediately posterior to the place of its confluence with the parieto-occipital sulcus (sulcus parietooccipitalis). In field 17 according to Brodmann, the spatial continuity of these projections is realized. A less clear-cut nature of the projections also occurs in the extrastriate fields (fields 18 and 19 according to Brodmann).

Fields 18 and 19 are located on the lateral surface of the occipital lobe: field 18 is closer to the pole of the occipital lobe, field 19 is closer to the parietal and temporal lobes. These fields are secondary zones of the visual analyzer. If the cortical neurons of field 17 perceive relatively simple visual signals, then more complex complexes of visual signals are perceived by receptive fields 18 and 19. Further information processing is carried out in the tertiary zone (overlap zone), located in the deep parts of the cortex of the occipital-parietal-temporal region.

Doesn't justify itself theory of double innervation of the macula. According to this theory, each point in the area of the macula of one eye, unlike other parts of the retina, is connected with the cortical centers of both hemispheres. Anatomical data do not confirm this.

The cortex of the occipital lobe is connected to the primary visual centers not only by centripetal, but also by centrifugal fibers that go from the cortex to the quadrigeminal region and the cushion of the visual thalamus. Centrifugal fibers pass through the inner sagittal layer of white matter around posterior horn lateral ventricle, they lie medial to the centripetal fibers. The ending of the centrifugal fibers in the quadrigeminal shows that this reflex center is influenced not only by stimulation from the periphery, but also by impulses coming from the occipital lobe cortex.

Article from the book: .

The optic nerve (II pair), in development, like the retina, is part of the brain and constitutes the initial section of the visual analyzer. Receptors of the visual analyzer in the form of rods (for black-and-white vision) and cones (for color vision) are located in the retina of the eye. The majority of cones on the retina are concentrated in the macula, which is the place of best vision. Impulses from rods and cones pass to bipolar ones, and from them to retinal ganglion cells, the axons of which form the optic nerve. The optic nerve includes fibers from the inner, outer retina and macula. The fibers coming from the macula make up the macular fascicle of the optic nerve. Thus, each optic nerve contains fibers from its own eye. Both optic nerves begin as discs (papillae) on the retina of the eyes, then through the optic canal of their side they enter the cranial cavity and, passing at the base of the frontal lobe of the brain, in front of the sella turcica they come together, making a partial decussation (chiasma opticum). In the chiasm, only the fibers coming from the inner (nasal) halves of the retina intersect. Fibers from their outer (temporal) halves do not decussate in the chiasm. Some of the fibers of the macular bundle also intersect.

1 - field of view; 2 - optic nerve; 3 - visual chiasm; 4 - visual path; 5 - external geniculate body; b - superior colliculi of the midbrain roof; 7 - thalamic cushion; 8 - visual radiance; 9 - cortical department of the visual analyzer; 10 - accessory nucleus of the oculomotor nerve; 11 - parasympathetic fibers of the oculomotor nerve; 12 - ciliary node.

After the optic chiasm, the right and left visual pathways (tracti optici) are formed, each of which contains fibers from both eyes - uncrossed fibers on their side and crossed from the opposite eye, i.e. fibers from the same halves of the retina of both eyes (right or left ). Each visual pathway is directed posteriorly and outward, bends around the cerebral peduncle and ends in two bundles in the subcortical visual centers: the first bundle in the external geniculate body and the thalamic cushion, the second in the superior tubercle of the quadrigeminal plate of the midbrain. In the subcortical visual centers there are neurons, the axons of which then go in different ways. From the external geniculate body and the thalamic cushion, optic fibers

pass through the posterior leg of the internal capsule and then, fanning out, form the optic radiance (Graciole bundle). Optic radiation fibers are directed through the deep sections of the temporal and partially parietal lobes to the cortex of the inner surface of the occipital lobe, where the cortical section of the visual analyzer is located in cytoarchitectonic field 17. It includes the calcarine groove and the gyri located on the sides of it: above - the wedge (cnneus), below - the lingual gyrus (gyrus lingualis), in which the fibers from the same halves of the retina of both eyes end. Impulses from this area enter the 18th and 19th cortical fields of the outer surface of the occipital lobe, where complex visual images are analyzed and synthesized, and recognition of what is seen occurs.

The optic tract fibers going to the superior tubercle of the midbrain roof plate take part in the formation of the reflex arc of the pupillary reflex (constriction of the pupils when the eyes are illuminated). Light stimuli entering the retina are first directed along the afferent part of the reflex arc, which consists of the optic nerve and optic pathway, to the superior tubercle of the roof plate. Then, through the intercalary neuron, they enter the parasympathetic nuclei of the oculomotor nerves (Yakubovich nuclei) of their own and the opposite side. From these nuclei, along the efferent part of the reflex arc as part of the oculomotor nerve, passing through the ciliary ganglion, impulses reach the muscle that constricts the pupil (m. sphincter pupillae). Since the visual fibers are connected to the parasympathetic nucleus not only on their side, but also on the opposite side, when one eye is illuminated, a constriction of both pupils occurs. The constriction of the pupil of the illuminated eye is called the direct reaction of the pupil to light. The simultaneous constriction of the pupil of the unlit eye is called the congenital reaction of the pupil to light.

Damage to different parts of the visual analyzer manifests itself clinically in different ways. Complete damage to the optic nerve of a traumatic, ischemic, inflammatory or other etiology leads to loss of vision in this eye (amaurosis), which is accompanied by loss of the rectum (since the afferent part of the reflex arc is interrupted) and the preservation of the friendly reaction of the pupil of the blind eye when the healthy eye is illuminated. Decreased vision resulting from damage to the optic nerve is called amblyopia. Partial damage to the optic nerve is accompanied by a narrowing of the field of vision or loss of its individual sections (scotoma). With pathology of the optic nerve in the fundus, primary atrophy of its disc is observed.

It is necessary to take into account that the refractive media of the eye (lens, vitreous body) project the reverse image of what is seen onto the retina, therefore objects from the right half of the visual field are perceived by the left half of the retina and vice versa. The field of view is the area of space that the fixed eye sees. As a result of damage to the visual pathway, subcortical and cortical visual centers, the perception of visual images falling on the same halves of the retina of both eyes is disrupted. In this case, the opposite halves of the visual fields become “blind”. This pathology is called hemianopsia (loss of half the visual field of each eye). In such cases, either the right or left halves of the visual fields are lost, therefore such hemianopsia is called homonymous (of the same name), left-sided or right-sided. Thus, damage to the left visual pathway causes right-sided hemianopia, and left-sided hemianopsia of the right. Damage to the optic radiation or the cortical part of the visual analyzer is rarely complete due to the wide distribution of fibers in them. Therefore, with partial damage to the optic radiance or damage to part of the cortical center of the visual analyzer (its upper or lower section), quadrant homonymous hemianopsia occurs - not half, but quadrants (quarters) of the visual fields of both eyes fall out. In the area of the wedge the upper quadrant of the retina of the same name is represented, in the area of the lingual gyrus the lower one. Therefore, for example, if the left wedge is damaged, the left upper quadrants of the retina will be “blind” and, accordingly, the lower right quadrants of the visual fields will fall out. When the left lingual gyrus is damaged, the upper right quadrants of the visual fields are lost.

Left-sided (a) and right-sided (b) homonymous hemianopsia with damage to the optic pathway or the lateral geniculate body.

Upper quadrant (a) and lower quadrant (b) homonymous hemianopsia with damage to the optic radiation or cortical part of the visual analyzer

Often in the clinic it is necessary to distinguish homonymous hemianopsia caused by damage to the visual pathway (tractus hemianopsia) from central homonymous hemianopsia that occurs when there is damage to the optic radiation or the cortical part of the visual analyzer in the area of the calcarine sulcus. To do this, it is necessary to take into account a number of signs.

Firstly, with tractus hemianopsia, retrograde degeneration of the axons of retinal ganglion cells develops with the appearance of primary atrophy of the optic discs in the fundus. In central homonymous hemianopsia, optic disc atrophy is not observed, since another neuron is damaged.

Secondly, due to the fact that the visual pathway is part of the afferent part of the reflex arc of the pupillary reflex, its damage is accompanied by the disappearance of the pupillary reaction when illuminated with a narrow beam of light using a slit lamp of the blind half of the retina. As a result of damage to the optic radiation or the inner surface of the occipital lobe, the reaction of the pupils to light is preserved when both the functioning and blind halves of the retina are illuminated.

Thirdly, with tractus hemianopsia, asymmetry of visual field defects is observed. Homonymous hemianopsia with damage to the optic radiance and cortical visual centers is characterized by a clear symmetry of defects in the visual fields of both eyes, which is explained by the peculiarity of the course of nerve fibers within the central part of the visual analyzer, where fibers from identical areas of the retina pass side by side.

Damage to the optic chiasm also causes visual impairment in both eyes. However, the nature of these changes will be different and depend on which part of the chiasm is affected. If the central part of the chiasm (crossed fibers) is affected, which occurs when it is compressed by a tumor of the pituitary gland, the inner halves of both retinas “blind.” Therefore, the patient does not see images from the outer (temporal) halves of the visual fields. In this case, the right half falls out of the field of vision of the right eye, and the left half of the left eye. This hemianopia is called heteronymous (different) bitemporal. Sometimes with an inflammatory process of the membranes at the base of the brain or a bilateral aneurysm of the intracranial part of the internal carotid arteries bilateral damage occurs only to the uncrossed fibers of the optic chiasm. In such cases, the outer parts of the retina become “blind” and the inner halves of the visual fields fall out, which leads to binasal heteronymous hemianopsia.

Limited defects in visual perception within the visual field are called scotomas, observed when the optic fibers are incompletely damaged. Pathological processes in the region of the occipital lobe, irritating visual centers lead to the appearance of photopsia (flickering sparks, stripes, glare) and visual or light hallucinations, which can be the aura of a generalized epileptic attack. Damage to the outer surface of the occipital lobe is sometimes accompanied by visual agnosia, when the patient does not recognize or distinguish objects by their appearance.

Study of the visual analyzer in neurological practice includes determination of visual acuity, examination of visual fields and fundus. Visual acuity is checked for each eye separately using special well-lit tables consisting of 12 lines of letters or rings (for the illiterate) or contour drawings (for children). The eye normally distinguishes letters on the 10th line at a distance of 5 m. Such vision is conventionally taken as 1. For example, if from such a distance the patient sees only the 5th line with the eye, visual acuity (visus) is 0.5, the 1st line is 0.1.

To study visual fields, a special device is used - a perimeter, the main part of which is a graduated arc rotating around the center. On outer surface arcs are marked from 0 to 90° on both sides of the middle. In the middle of the inner surface of the arch there is a fixed fixation mark on which the patient fixes his gaze. The boundaries of the visual field for each eye are checked separately. The other eye is closed during the examination. The patient notes the moment when he notices the appearance in the field of vision of another white mark (1-2 mm in diameter), which is moved from the outside to the middle in different planes along the inner surface of the perimeter arc. This position in degrees is marked graphically on the coordinate axes on the diagram of the field of view. Rotating the perimeter arc, conduct a study along the meridians every 15°. The points marked on the diagram are connected and the boundaries of the field of view are obtained. Normally, the outer limit of the visual field is 90°, the upper and inner borders are 50-60°, and the lower border is about 70°. Therefore, the image of the visual field of a healthy eye on the graph looks like an irregular ellipse, elongated outward. An approximate idea of the state of the visual field for each eye separately (the other eye is closed) can be obtained from the patient in a supine position by asking him to halve a stretched towel or string located in front of the eye in a horizontal plane. With homonymous hemianopia, the patient will divide in half only the section of the towel that he can see, not seeing about a quarter of its length.

a - normal; b - congestive optic disc; c - primary atrophy of the optic nerve head.

The condition of the optic nerve head is studied by examining the fundus of the eye using an ophthalmoscope. Normally, the optic disc is round, with clear boundaries, and pale pink in color. The branches of the central retinal artery extend radially from the center of the disc and converge in its center the retinal veins. The ratio of the diameter of arteries and veins is 2:3. When the axons of retinal ganglion cells are damaged at any interval (optic nerve, optic chiasm or optic tract), after some time these fibers degenerate and atrophy of the optic nerve head occurs, which is called primary. In such cases, the disc becomes pale, silvery-white. With increased intracranial pressure (mostly when the tumor is localized in the posterior cranial fossa) swelling of the optic discs occurs in the form of congestive discs. Stagnant disk increased in volume, its boundaries are unclear, the disc protrudes into the vitreous body, the arteries are narrowed, the veins are dilated. If the cause of hypertensive syndrome is not eliminated, stagnation of the optic discs over time turns into their secondary atrophy.