What function does the optic nerve perform? Optic nerve: functioning features and typical diseases

Anatomy of the organs of vision. Structure of the eyeball and optic nerve

The development of the human eye begins in the second week of embryonic life from the brain tube. At the end of the fourth week, the lens appears, around which choroid. The sclera and chambers of the eye gradually differentiate, and the vitreous body becomes transparent. From skin folds eyelids are formed.

Organ of vision - Visual analyzer consists of three main sections: peripheral or receptor (in the retina), conductive (includes visual pathways and oculomotor nerves) and cortical (occipital lobe of the cerebral cortex).

Peripheral, receptor part consists of eyeballs, as well as adnexal and protective apparatuses. They are the eye socket, external eye muscles with vessels, nerves, fatty tissue of the orbit and connective tissue, eyelids, as well as organs that secrete and conduct tear fluid. These accessory and protective organs ensure the fulfillment physiological function eye

Orbit.

The orbit, or eye socket, is the bony container for the eye. In shape it resembles a tetrahedral pyramid, the apex of which faces the cranial cavity, and the base faces anteriorly. The orbit is formed by the bones of the skull: frontal, zygomatic, upper jaw, nasal, lacrimal, ethmoidal and sphenoid. The anatomical connection of the orbit with the paranasal sinuses is often the reason for the transition of the inflammatory process or tumor growth from them into the orbit. There are four walls in the orbit: upper, lower, inner and outer.

At the apex of the orbit there is round shape with a diameter of 4 mm, the optic foramen through which the orbital artery enters the orbital cavity and the optic nerve exits into the cranial cavity. The contents of the orbit consists of the eyeball, fiber, fascia, muscles, blood vessels, and nerves. There are eight muscles in the orbit. Of these, six are oculomotor (4 direct and 2 oblique), the levator muscle upper eyelid and orbital muscle.

Eyelids.

The eyelids are movable skin-muscular folds that cover the front of the eyeball. They form a palpebral fissure. Consist of five layers: leather, loose subcutaneous tissue(does not contain fat), orbicularis oculi muscle, cartilage, conjunctiva.

Functions eyelids: - protect the eyes due to reflex closure under the influence of irritating influences.

Conjunctiva.

This is a connective membrane that covers the front of the eyeball (except for the cornea) and the eyelids. inside. It is thin, transparent, pink, smooth, shiny, moist. When the eyelids are closed, the conjunctiva forms a slit-like cavity - the conjunctival sac.

Functions of the conjunctiva:

Protective (if it enters the conjunctival cavity foreign body or in a pathological process)

Mechanical (abundant secretion of tear and mucous fluid)

Moisturizing (constant secretion production)

Nutrient (from its vessels through the cornea nutrients enter the eye)

Barrier (rich in lymphoid elements).

Lacrimal apparatus.

The lacrimal apparatus consists of the lacrimal gland and lacrimal ducts (lacrimal puncta, lacrimal canaliculi, lacrimal sac and nasolacrimal canal).

The lacrimal gland is located in a depression in the superior outer wall of the orbit.

Functions of the lacrimal gland: tear production (after the second month of life). At rest, a person produces about 1 ml of tears per day.

Tear distributed evenly over the surface of the eyeball, absorbed by the upper and lower lacrimal openings, from there it enters the upper and lower lacrimal canaliculi. The tubules, connecting into a common lacrimal canaliculus, flow into the lacrimal sac. The lacrimal sac passes into the nasolacrimal canal, which opens under the inferior nasal concha.

Functions of a tear: bactericidal (contains the enzyme lysozyme), nourishing (contains 98% water, 0.1% protein, 0.8% mineral salts, potassium, sodium, chlorine, glucose and urea), moisturizing (provides constant hydration of the eyeball).

Muscular apparatus.

The eyeball has six oculomotor muscles– four straight lines (upper, lower, outer, inner) and two oblique (lower and upper). These muscles provide good mobility in all directions.

The structure of the eyeball.

The eyeball has an irregular spherical shape. The average size of the eyeball in an adult is 24 mm.

The eyeball has three membranes:

1. external (fibrous) – consists of the sclera and cornea

2. middle (vascular) - consists of the iris, ciliary body and the vascular itself (choroid).

3. internal – retina.

Outer shell.

Sclera– outer, opaque, dense, consists of collagen fibers.

Functions: protective, shape-forming, ensures turgor of the eyeball. The junction of the sclera and the cornea is called the limbus.

Cornea- the anterior, more convex part of the outer shell of the eye. It is transparent, avascular, smooth, mirror-like, shiny, spherical, highly sensitive (it contains a large number of sensitive nerve endings).

Functions: refraction of light (refractive power - 40D for adults and 45D for children), protective. The horizontal diameter of the cornea in newborns is 9 mm, at 1 year - 10 mm, in adults - 11 mm.

2. Choroid.

It consists of the iris, ciliary body and choroid.

All three sections of the choroid are combined under the name uveal tract.

Iris- is a diaphragm, in the center of which there is a hole - the pupil. The pupil can dilate (in the dark) and constrict (in bright light). The color of the iris depends on the amount of pigment. The permanent color of the iris is formed only by the age of 2. The iris contains many sensory nerve endings.

Functions: takes part in the filtration and outflow of intraocular fluid.

Ciliary body– located between the iris and the choroid itself. The ciliary body contains many sensory nerve endings. The ciliary body has the same source of blood supply as the iris (anterior ciliary arteries, posterior long ciliary arteries). Therefore, its inflammation (cyclitis), as a rule, occurs simultaneously with inflammation of the iris (iridocyclitis).

Functions: production of intraocular fluid, participation in the act of accommodation. The ligaments of Zinn come from it and are woven into the lens capsule.

The choroid itself or choroid is posterior section vascular tract, located between the retina and sclera.

Functions: provides nutrition to the retina, takes part in ultrafiltration and outflow of intraocular fluid, regulation of ophthalmotonus. There are no sensitive nerve endings in the choroid; as a result, its inflammation, injuries and tumors are painless. The blood supply to the choroid is carried out from the posterior short ciliary arteries, therefore its inflammation (choroiditis) occurs in isolation from inflammatory processes anterior part of the uveal tract. Blood flow in the choroid is slow, which contributes to the occurrence of tumor metastases in it various localizations and sedimentation of pathogens of various infectious diseases.

Inner shell.

Retina represents a highly differentiated nerve tissue. This is the peripheral part visual analyzer. It has photoreceptors - rods and cones. Cones carry out central vision, day vision and color perception. Rods – peripheral vision, night and twilight vision. There are no sensitive nerve endings in the retina, so all its diseases are painless. The inner surface of the eyeball is called the fundus. There are two important formations in the fundus of the eye: the optic disc (where the nerve exits the retina) and the macula area. In the central fovea of the macula, only cones are located, which provides high resolution of this zone. Beginning on the fundus in the form of a disk, the optic nerve leaves the eyeball, then the orbit and in the area of the sella turcica it meets the nerve of the second eye. In the sella turcica there is an incomplete crossing of the optic nerves, called the chiasma. After partial decussation, the visual pathways change their name and are called optic tracts. The visual tracts are directed to the subcortical visual centers and further to the visual centers of the cerebral cortex - the occipital lobes.

Functions: light-perceiving, light-conducting.

The space between the cornea and iris is called anterior chamber of the eye.

Front Cam Angle ry - the space where the iris passes into the ciliary body, and the cornea into the sclera. In the corner of the chamber there is a helmet channel.

The space between the iris and lens is called posterior chamber of the eye. The posterior chamber communicates with the anterior chamber through the pupil. The chambers of the eye are filled with clear intraocular fluid. Complete exchange of chamber moisture occurs within 10 hours. It contains water, mineral salts, vitamins B2, C, glucose, oxygen, protein. The intraocular fluid, through Schlemm's canal and the venous system, removes metabolic products (lactic acid, carbon dioxide, etc.) from the eye. The chambers of the eye communicate with each other through the pupil.

Lens– is a biconvex lens located between the iris and the vitreous body. It is formed at 3-4 weeks of life of the embryo from the ectoderm. It has no nerves, blood or lymphatic vessels.

Functions: refraction (refractive power - 20.0 D), participation in the act of accommodation.

Vitreous body– located behind the lens and makes up 65% of the contents of the eye. It is transparent, colorless, gel-like. There are no vessels or nerves in the vitreous body. Contains up to 98% water, little protein and salts.

Functions: supporting tissue of the eyeball, ensures the free passage of light rays to the retina, passively participates in the act of accommodation, protective (protects the inner membranes of the eye from dislocation).

Optical system of the eye- this is the cornea, the moisture of the anterior and posterior chambers, the lens and the vitreous body. Passing through these formations, light rays are refracted and hit the retina.

The act of seeing– a complex neurophysiological act consisting of 4 stages:

1 – with the help of the optical media of the eye, an inverted image of objects is formed on the retina.

2 – under the influence of light energy, a complex photochemical process occurs in the rods and cones, as a result of which a nerve impulse arises.

3 – impulses originating in the retina are carried along nerve fibers to the visual centers of the cerebral cortex.

4 – in the cortical centers, the energy of the nerve impulse is converted into visual sensation and perception. The visual analyzer consists of three main sections: receptor (in the retina), conductor (includes the visual pathways and oculomotor nerves) and cortical (occipital lobe of the cerebral cortex).

Rice. 2.3. Diagram of the structure of the eyeball (sagittal section).

Optic nerve

The complex system of cranial nerves includes the optic nerve. The optic nerve is not like other cranial nerves because it is more of a part of the white matter of the brain that is located outside of the brain. The optic nerve and retina are connected through retinal ganglion cells and the optic disc. The innervation of the retina transmits nerve impulses to the optic nerve and further to the brain. The optic nerve is “braided” by the retinal artery, which is responsible for supplying blood to the retina.

29. Formation of the visual analyzer in ontogenesis .

As is known, the visual analyzer consists of three sections: peripheral, or receptor, intermediate, or conductive, and central, or cortical.

The peripheral section is represented by two retinas, enclosed in unique optical cameras, which provide the receptor with clear images of objects in the surrounding world.

The intermediate, or conductive, section begins in the layer of retinal ganglion cells and ends in the cortex of the occipital lobe. The optic nerves, chiasm and optic tracts constitute the first neuron of this section.

The cortical nucleus of the visual analyzer is a section of the occipital lobe of the cerebral cortex.

In ontogenesis, the peripheral part of the analyzer is the first to form and mature, then the conductive part, and only after that the cortical part.

The maturation of the visual analyzer in embryogenesis occurs later than other sensory systems, but by the time of birth the peripheral part of the visual analyzer reaches a significant level of development. TO age characteristics visual analyzer includes the following.

Peripheral department. The embryonic development of the visual analyzer begins relatively early (at 3 weeks) and by the time the child is born, the visual analyzer is morphologically formed. However, the improvement of its structure occurs even after birth, ending already in the school years.

The organ of vision is the eye. The shape of the eye is spherical, in adults its diameter is about 24 mm, in newborns it is 16 mm, and the shape of the eyeball is more spherical than in adults. As a result of this, newborn children have a farsighted reaction in 80 to 94% of cases. The growth of the eyeball continues after birth, but is most intense in the first 5 years of life and less intense until 10-12 years.

In a newborn, the movement of the eyeballs occurs independently of each other. If one eye is motionless, the other can move. The eyes can even move in opposite directions. In other words, newborns experience physiological strabismus. By the end of the 1st month of life, coordination in eye movements begins to appear; in the second month they move in a friendly manner.

The cornea in children (newborns) is thicker and more convex. By the age of 5, the thickness of the cornea decreases, due to which its refractive power also decreases (due to compaction). The lens in newborns and preschool children is more convex, transparent and more elastic.

The pupil of newborns is narrow. At 6-8 years old, the pupils are wide due to the predominance of the tone of the sympathetic nerves innervating the muscles of the iris (radial and annular). At 8-10 years of age, the pupil becomes narrow again and reacts very quickly to light. By the age of 12-13 years, the speed and intensity of the pupillary reflex to light is the same as in adults.

Lacrimal glands are already developed in newborns, but nerve pathways They ripen only by 3-5 months. Therefore, children in the first months of life cry without tears.

In newborns, the receptors in the retina are differentiated, and the number of cones in macula begins to increase after birth and by the end of the first half of the year the morphological development of the central part of the retina ends. In the first year of life, children cannot distinguish colors, since the cones have not yet matured functionally. In the second year of life, cones mature and the child begins to distinguish simple colors. Cones begin to fully function by the end of the 3rd year of life (distinguishes complex colors).

Accommodation is the ability of the eye to clearly see objects at different distances due to changes in the curvature of the lens. The maximum power of accommodation at the second stage of development is 20 diopters (the nearest point of clear vision is at a distance of 5 cm from the eye, at the 4th stage of development - 8 cm, in an adult - 10 cm). A decrease in the magnitude of accommodation begins at the age of 10, although this practically does not affect vision for many years. The main reason for the decrease in accommodation is the compaction of the lens, the loss of elastic properties - it loses its ability to change its curvature.

Field of view - is formed in ontogenesis for quite a long time late stages. In children, peripheral vision appears only by 5 months of life. Until this time, they fail to evoke a defensive blink reflex when an object is introduced from the periphery. With age, the field of vision increases. A particularly strong expansion of the boundaries of the visual field is observed in the period from 6.5 to 7.5 years, when the size of the visual field increases approximately 10 times. Expansion continues until 20-30 years of age. In old age, the value of this indicator decreases somewhat. Age-related changes depend on a number of factors, including profession.

Wiring department. During the first days, children cannot see, since the conductive section of the visual analyzer has not yet matured. Its growth and development is uneven.

Central department. Differentiation central department The cortical representation of the visual analyzer in humans does not end even at the time of birth. The cortical section develops later than the peripheral and conductive sections. Although the area of the cortex in a newborn has all the signs of the adult cortex, it has a smaller thickness (1.3 mm instead of 2 mm in an adult) and a denser arrangement of cells; its formation ends by the age of 7.

The light-receiving function develops most early in ontogenesis. The presence of light perception in very young children can be judged by the reflex reactions that occur in bright light (pupillary reflex, closing of the eyelids and abduction of the eyes).

Measuring sensitivity to light in children using adaptometers becomes possible from the age of 4-5. Studies have shown that sensitivity to light increases sharply in the first two decades and then gradually decreases.

In the second month of life, the child sees images of objects, but upside down. However, within a year, thanks to the analytical and synthetic activity of the central department of the visual analyzer, the child begins to see images of objects correctly.

Fixation of gaze on the object in question is formed by 3-4 months. Before this, the child’s gaze wanders and if it accidentally stops on an object, the child begins to examine this object. The ability to fixate the gaze on the object in question is associated with the mental development of the child. If he does not learn to fix his gaze within a year, then this indicates dementia.

Visual acuity is very important characteristic visual analyzer, measured not only by the ability of the cone apparatus, but also by the transparency of the cornea and vitreous, the focusing ability of the lens, its astigmatic properties. It is difficult to determine this indicator in children. For children under 1 year of age, a ball on a thin thread is inserted into the child’s field of vision at different distances from the eyes. The distance at which the child stops following the ball characterizes his visual acuity. Measurement different authors showed that visual acuity in the first months and even years of life is lower than in an adult. In the period from 18 to 60 years, visual acuity remains virtually unchanged, and then decreases. Moreover, with age, the distribution of people with different visual acuities also changes. Percentage of people with normal vision decreases with age.

Optic nerve. Structure, anatomy, research methods.

The optic nerve ensures the transmission of nerve impulses from light stimulation going from the retina to the visual center, which is located in the occipital lobe of the brain.
The optic nerve consists of nerve fibers of the sensory cells of the retina, which are collected in a bundle at the posterior pole of the eyeball. Total number There are more than a million such nerve fibers, but their number decreases with age. Location of nerve fibers from different areas the retina has a certain structure. Approaching the area optic disc(ONH) the thickness of the layer of nerve fibers increases, and this place rises slightly above the retina. Afterwards, the fibers collected in the optic nerve head are refracted at an angle of 90˚ and form the intraocular part of the optic nerve.

The diameter of the optic nerve head is 1.75-2.0 mm, it is located on an area of 2-3 mm. The area of its projection in the field of view is equal to the area of the blind spot, discovered back in 1668 by the physicist E. Marriott.

The length of the optic nerve continues from the optic disc to the chiasm (the place of optic nerve chiasm). Its length in an adult can be 35 - 55 mm. The optic nerve has an S-shaped bend that prevents it from being pulled during eyeball movement. Almost along its entire length, like the brain, the optic nerve has three membranes: hard, arachnoid and soft, the spaces between which are filled with moisture complex composition.

The optic nerve is usually divided topographically into 4 parts: intraocular, intraorbital, intracanalicular and intracranial.

The optic nerves of the eyes enter the cranial cavity and form a chiasm, uniting in the area of the sella turcica. In the area of the chiasm, partial crossing of the optic nerve fibers occurs. Fibers leading from the inner halves of the retina (nasal) undergo crossing. The fibers leading from the outer halves of the retina (temporal) do not cross.

After crossing, the optic fibers are called optic tracts. Each tract consists of fibers from the outer half of the retina on the same side, as well as the inner half of the opposite side.

Function of the optic nerve is the transmission of impulses from the photoreceptors of the retina to higher structures that are located in the cortex of the occipital lobes of the brain. As a result, the formation of a visual image becomes possible. In addition, based on the connections of the central structures with each other, visual memory is also formed.

Research methods:

1) visual acuity test using tables (currently the table of Golovin, Sivtsev)

Determination of visual acuity is carried out using special tables on which there are 10 rows of letters or other signs of decreasing value. The subject is placed at a distance of 5 m from the table and names the symbols on it, starting from the largest and gradually moving to the smallest. Each eye is examined separately. Visual acuity is 1 if the smallest letters can be distinguished on the table; in the same cases when only the largest ones are distinguished, visual acuity is 0.1, etc. Near vision is determined using standard text tables or maps. Counting fingers, finger movements, and perception of light are noted in patients with significant visual impairment.

For children over 5 years old, the table is used. Orlova with the most familiar toys.

This table contains rows with pictures, the size of which decreases from row to row in the direction from top to bottom.

2) visual field examination

Perimetry is a technique for studying visual fields with their projection onto a spherical surface. Visual fields are those parts of space that the eye sees with a fixed gaze and a motionless head. When the gaze is fixed on a certain object, in addition to a clear visualization of this object, other objects are also visible that are at different distances and fall into the field of view. This makes it possible peripheral vision, which is less clear than the central one.

The study is carried out using special instruments - perimeters shaped like an arc or hemisphere. This method The examination is carried out for each eye separately, while a bandage is fixed on the second eye. During the study, the patient sits in front of the perimeter, places his chin on a special stand, while the eye being examined is located exactly opposite the point that should be fixed with his gaze.

When performing perimetry, the patient looks at the indicated point without looking away. The doctor is on the side, moving the object along the meridians from the periphery to the center. In this case, the patient needs to catch the moment when, with his gaze fixed on a point in the center, he sees a moving object. The ophthalmologist notes the indicators on a special chart. The movement of the object should continue until the fixation point in order to make sure that vision is preserved throughout the entire meridian. The size of the object used depends on the visual acuity. For high visual acuity, an object with a diameter of 3 mm is used; for low visual acuity, an object with a diameter of 5 to 10 mm is used. Typically, the study is carried out along eight meridians, sometimes for a more accurate picture - along 12 meridians.

There is no color perception in the peripheral parts of the retina. The extreme periphery perceives only white color; as you approach the central zones, the sensation of yellow, blue, green and red colors appears. And only the central zone perceives all colors.
The field of vision of each eye to a white object normally has the following boundaries:

outward (towards the temple) – 900,
outwards upwards – 700,
top – 50-550,
from inside to top – 600,
inwards (toward the nose) – 550,
from inside to bottom – 500,
downwards – 65-700,
from outside to bottom – 900.

Acceptable deviations are from 5 to 100. Visual fields for other colors are examined in the same way as for a white object. But at the same time, the patient needs to record not the moment when he sees the movement, but the moment when the color of the object is discernible. Quite often, while the boundaries of the visual fields to a white object are preserved, narrowings to other colors are revealed.

3) Fundus examination carried out with an ophthalmoscope.

When the axons of ganglion cells are damaged along any part of their path, degeneration of the optic nerve head tissue occurs over time - primary atrophy. With primary atrophy, the optic disc retains its size and shape, but its color fades and may become silvery-white.

If the patient has increased intracranial pressure, then the venous and lymphatic outflow from the retina of the eye is disrupted, which leads to swelling of the optic nerve head. As a result, the so-called congestive optic disc develops. It is enlarged in size, its boundaries are blurred, and the edematous tissue of the disc often protrudes into the vitreous body. The arteries narrow, the veins at the same time become dilated and tortuous. With pronounced symptoms of stagnation, hemorrhages occur in the disc tissue.

Stagnant discs, if their cause is not promptly eliminated, can go into a state of atrophy. At the same time, their sizes decrease, but usually they still remain somewhat larger than normal, the veins narrow, the boundaries become clearer, and the color becomes pale. In such cases, they speak of the development of secondary atrophy of the optic discs. The ophthalmoscopic picture of optic neuritis and congestion in the fundus have much in common, but with neuritis, the visuus usually falls sharply and turns out to be low from the onset of the disease, and with congestion, the visuus can remain satisfactory for a long time, and a significant drop occurs only with the transition of the congestive disc to atrophic.

When a long-standing tumor of the base of the brain compresses one of the optic nerves, primary atrophy of the optic disc occurs on the affected side and secondary atrophy on the opposite side due to the development of intracranial hypertension.

4) Study of color perception

To study color vision, two main methods are used: special pigment tables and spectral devices - anomaloscopes. Of the pigment tables, Rabkin's polychromatic tables are recognized as the most perfect.

The tables are original drawings that depict dots and circles of different colors and diameters. If you have color blindness, a person can easily distinguish the brightness of a color, but it is difficult for him to characterize the color itself. Rabkin's scheme takes these features into account - the brightness of the icons is the same, but the color differs. A person with a deviation in color perception will not see an image hidden in a different color in a diagram.

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The optic nerve belongs to the optical system and is a link that connects the central structures of the brain with. The visual center is located in the cortex cerebral hemispheres (occipital region) and is the highest organ responsible for vision.

Structure of the optic nerve

The optic nerve consists of a large number (more than a million) sensory neurons. Long sensitive endings extend from these cells, which are processes of cells that are located in. As the body ages, the amount nerve cells gradually decreases, and new neurons are no longer formed. This is one of the reasons age-related decline visual acuity. With an increase in the diameter of the nerve fibers, the formation of the optic nerve disc occurs, which is localized in the central zone of the retina. The doctor also evaluates the condition of this disc. The intraocular part of the optic nerve extends at an angle of 90 degrees.

The diameter of the optic nerve disc is about 1.5-2 mm. Due to the absence of photoreceptors in this area, this zone corresponds to the one that is projected into the visual field. After the fibers depart, they go deep into the brain, on the basis of which they form the so-called chiasma (cross). Due to the presence of a chiasm, when the right part of the optic nerve is damaged, vision decreases on the left, and vice versa.

It should not be forgotten that the decussation of nerve fibers in the area of the chiasm is not complete. It affects only those neurons that receive information about the visual image from the half of the retina located medially, that is, closer to the nose. Also, in the area of the decussation, an S-shaped deviation of the nerve fiber occurs, which helps to reduce the tension of the processes. Due to this mechanism, the nerve is not injured or stretched when moving the eyeballs.

The optic nerve itself consists of three membranes, which are similar to the covering of the brain:

The dura shell is the outermost;
Arachnoid – intermediate;
Soft - inner shell.

The optic nerve consists of four sections:

Cranial;
Orbital;
Canalicular;

Physiological role of the optic nerve

The function of the optic nerve is to transmit impulses from the photoreceptors of the retina to higher structures located in the cortex of the occipital lobes of the brain. As a result, the formation of a visual image becomes possible. In addition, based on the connections of the central structures with each other, visual memory is also formed.

Video about the structure of the optic nerve

Symptoms of optic nerve damage

If the optic nerve is damaged, the patient may experience the following symptoms:

Narrowing of the field of view;
Color vision impairment;
Decreased visual acuity;
The appearance of flashes, lightning, glare, etc.;
Appearance.

Diagnostic methods for damage to the optic nerve

If involvement of the optic nerve in the pathological process is suspected, a number of studies should be performed:

Coherence optical tomography;
Ophthalmoscopy.

It should be recalled once again that the optic nerve is an integral component optical system. It is responsible for communication between retinal receptors and central structures, which are localized in the cerebral cortex. Only thanks to the work of the optic nerve does it become possible to form an image and visual memory.

Optic nerve diseases

Among the diseases that lead to damage to the optic nerve are:

Optic nerve atrophy;
Coloboma of the disc;
Aplasia and hypoplasia of neurons and disc;
Neuritis.

All these diseases lead to disruption of the optical system, including irreversible loss of vision. This, in turn, greatly affects the quality of life.

Which are collected in a bundle at the posterior pole of the eyeball. The total number of such nerve fibers is more than a million, but their number decreases with age. The location of nerve fibers from different areas of the retina has a certain structure. Approaching the area of the optic nerve head (OND), the thickness of the layer of nerve fibers increases, and this place rises slightly above the retina. Afterwards, the fibers collected in the optic nerve head are refracted at an angle of 90˚ and form the intraocular part of the optic nerve.

The diameter of the optic nerve head is 1.75-2.0 mm, it is located on an area of 2-3 mm. The area of its projection is equal to the area of the blind spot, discovered back in 1668 by the physicist E. Marriott.

The optic nerve is usually divided topographically into 4 parts: intraocular, intraorbital, intracanalicular and intracranial.

After crossing, the optic fibers are called optic tracts. Each tract consists of fibers from the outer half of the retina on the same side, as well as the inner half of the opposite side.

Methods for studying the optic nerve and optic disc

The optic disc can be examined and examined in detail using the following methods:

Ophthalmoscopy of the optic disc with assessment of color, shape, borders, vessels.

Campimetry, which determines the central spot in the field of vision, as well as the size of the blind spot.

Optical coherence tomography OCT.

Optic nerve diseases

The above studies can reveal the following congenital pathologies:

Increasing the size of the optic disc

Aplasia and hypoplasia of the optic disc

Disc drusen

Atrophy of the optic disc

False neuritis

Acquired disorders are also quite numerous:

Atrophy of the optic disc of various origins.

Congestive optic nerve disc and true neuritis.

Vascular disorders - dilation of veins, narrowing of arteries.

All these pathological changes The optic nerve may exhibit the following symptoms:

Altered color perception.

Violations of the visual field of the affected eye, with localization of the lesion in both eyes above the chiasm.

Increased threshold of electrical sensitivity of the optic nerve.

Optic nerve (n.opticus)- begins with a disk, which is formed by the axons of retinal ganglion cells, and ends in the chiasm. The optic nerve has four sections: intraocular (with prelaminar, intralaminar and postlaminar parts), orbital, intracanalicular and intracranial. The total length of the optic nerve varies in adults from 35 to 55 mm. A significant part of it is the orbital process (25 - 30 mm), which in the horizontal plane has an S-shaped bend and thanks to this the optic nerve does not experience tension when the eyeball moves. The axons of all retinal ganglion cells ultimately gather at the posterior pole of the eye into the optic nerve, the initial (intraocular) part of which is called the disc. Since the layer of nerve fibers and the entire retina protrude into the eye in the form of a papilla, hence its former name - papilla n.optici (papilla of the optic nerve).

Total number of nerve fibers components of the optic nerve head (OND), reaches 1200000 , but with age their number gradually decreases. The topography of this zone is distinguished by a strict pattern. From the macular region of the retina to the middle-temporal part of the optic disc there is a short but dense bundle of axons, which pushes the arc fibers emanating from the superior and inferior temporal quadrants of the retina into its corresponding segments. Radial fibers extending from the superior and inferior nasal quadrants of the retina occupy segments of the same spatial orientation in the optic nerve head. Then the fibers collected in it make an arcuate bend (at 900) and form the initial part of the optic nerve in the form of separate bundles.

Anatomical parameters of the optic disc: length about 1 mm, diameter 1.75-2.0 mm, area - 2-3 mm2 (more detailed parameters of the optic disc are given in the section "24 mm"). The optic disc is slightly displaced towards the nose from the posterior pole of the eye (4 mm) and slightly below it. According to the projection of the optic disc into space, there is a blind spot (physiological scotoma) in the temporal half of the visual field of each eye. It was first discovered in 1668 by the physicist E. Mariotte (when examining the visual field, a physiological negative absolute scotoma is diagnosed, which is a projection of the optic nerve head. The reason for the occurrence of scotoma is that the area of the disc is devoid of light-receiving elements). According to the tissue structure of the optic disc, it belongs to the so-called non-pulp nerve fibers, i.e. it itself is deprived of all meninges, and the nerve fibers that make it up - myelin fibers - have a myelin sheath. There are also no oligodendroglia and microglia in it. But the optic disc is richly equipped with vessels and supporting elements. Its neuroglia consists exclusively of astrocytes with long processes that surround all bundles of fibers and, penetrating into them, accompany each fiber. Astrocytes also take part in the formation of the lattice support structure of the optic disc and separate it from neighboring tissues. The border between the pulpless and pulpal sections of the optic nerve coincides with the outer surface of the lamina cribrosae, i.e. still located inside the eye. The non-pulpal portion of the optic nerve is divided into three parts(according to Salzmann M., 1913): retinal, choroidal and scleral. The retinal part of the optic disc is a ring, the temporal half of which is lower than the nasal half, since it contains thinner layer nerve fibers. The latter, after the above-mentioned arcuate bend, form a depression in its middle either in the form of a funnel (called vascular) or in the form of a ring (physiological excavation). The retinal vessels passing here are covered with a thin sheath of glia, which forms a connecting cord at the bottom of the physiological excavation. The retinal part of the optic disc is separated from the vitreous body by a non-continuous glial membrane, described by A. Elshning (Elshning A., 1899). The main layers of the retina - from the layer of ganglion cells to the layer of rods and cones inclusive - end at the edge of the optic disc, and the inner layers end before the outer ones, which is due to the passage of ganglion cell axons into them. The choroidal part of the optic disc consists of the above-mentioned bundles of nerve fibers, covered with astroglial tissue with transverse branches that form a lattice structure. The basal lamina of the choroid has a rounded hole in this place (for. optica choroideae), which is connected by a channel to the cribriform plate of the sclera (lamina cribrosa). The length of this chorioscleral canal is 0.5 mm, the diameter of the internal opening is about 1.5 mm, and the external one is slightly larger. This layer of the optic disc is equipped with a dense network of capillaries.

The scleral part of the optic disc is represented, as can be seen from the above, only with fibers passing through the cribriform plate of the sclera. The blood supply to the optic disc is carried out, mainly due to the posterior short ciliary arteries with insufficiently developed anastomoses. For this reason, the nutrition of its tissue is segmental in nature, which immediately manifests itself when blood flow in one of the arteries is disrupted. According to some data, the central retinal artery is involved in the blood supply to the retinal part of the optic nerve head. Over a considerable distance (from the exit from the eyeball to the entrance to the canalis opticus), the nerve, like the brain, has three membranes: the hard arachnoid and the soft. Together with them, its thickness is 4 -4.5 mm, without them - 3 -3.5 mm. The eyeball has a hard meninges fuses with the sclera and Tenon's membrane, and at the optic canal with the periosteum. The intracranial segment of the nerve and the chiasm are located in the subarachnoid chiasmatic cistern, dressed only in a soft shell. The intrathecal spaces of the orbital part of the nerve (subdural and subarachnoid) are connected to similar spaces in the brain, but are isolated from each other. They are filled with a fluid of complex composition (intraocular, tissue, cerebrospinal fluid). Since intraocular pressure normally exceeds twice the intracranial pressure (10 -12 mm Hg), then the direction of fluid flow coincides with the pressure gradient. The exception is cases when intracranial pressure increases significantly or the tone of the eye sharply decreases.

Subdural space The optic nerve looks like a narrow gap with crossbars running from the hard shell to the soft shell. Subarachnoid space somewhat wider than the subdural and includes complex system from crossbars that connect the soft and arachnoid membrane. From the soft membrane covering the orbital part of the optic nerve, numerous processes (septa) extend into it, which create a connective tissue base and divide the nerve fibers into separate bundles. At a distance of 7-12 mm from the eye and below, the central connecting cord enters the trunk of the optic nerve, which is a tube-shaped continuation of the soft shell. It bends almost at a right angle towards the axis of the nerve and reaches its disc. The cord includes the central arteries and veins of the retina and is connected to them by loose tissue. The bulk of the optic nerve consists of centrifugal fibers - the axons of retinal ganglion cells already mentioned above. The total number of them according to P. Eisler (1930) reaches 1 million. The cross-sectional diameter of one fiber is 0.002 -0.01 mm. All nerve fibers that make up the optic nerve are grouped into three main bundles. The axons of ganglion cells extending from the central (macular) region of the retina constitute the papillo-macular fascicle, which enters the temporal half of the optic nerve head. Fibers from the ganglion cells of the nasal half of the retina go along radial lines to the same half. Similar fibers, but from the temporal half of the retina, along the path of the optic nerve head, “flow around” the papillo-macular bundle above and below. In the orbital segment of the optic nerve near the eye, the relationships between nerve fibers remain the same as in its disc. Next, the papillo-macular one moves to the axial position, and the fibers from the temporal quadrants of the retina move to the entire corresponding half of the optic nerve. Thus, the optic nerve is clearly divided into right and left halves. Its division into upper and lower halves is less pronounced. Clinically important is the fact that that the nerve is devoid of sensory endings. In the cranial cavity, the optic nerves connect above the area of the sella turcica, forming chiasmus. In the area of the chiasm, the fibers of the optic nerve partially intersect due to portions associated with the nasal halves of the retinas. Moving to the opposite side, they connect with fibers from the temporal halves of the retinas of the other eye and form visual track - tr.opticum. The papillo-macular bundles also partially intersect here. It should be emphasized once again that in the optic nerve, optic tract and in visual radiance - radiato optica, starting from the neurons of the lateral geniculate body, the fibers are located in a strict retinotypic order. A similar order is observed in the cortical visual field, located in the occipital lobe, in the area of the calcarine groove - sulcus calcarinus.

The optic nerve consists of four sections, which are divided conventionally based mainly on its topography.

Intrabulbar department

The axons of the ganglion cells of the retina itself play a major role in the structure of the optic nerve. These axons, passing through the inner layer of the retina, flow to the pole of the posterior eye and form the optic disc at the exit point. In this case, the axons, the course of which comes from the periphery, lie outside, and the axons that later join them lie inside.

The optic fibers have an arcuate bend. This affects the fact that the optic nerve nipple has a small depression in its center, the anatomy of which resembles a funnel in shape (the so-called physiological excavation). Through this funnel the retinal vein and central artery pass into the eye. Latest in embryonic period development also penetrates the vitreous body.

The area of physiological excavation is covered from above by a glial cover, in which there is an admixture connective tissue, denoted by the term “Kunt’s connective tissue meniscus”. The optic disc is devoid of photoreceptors. In relation to the macula of the eye, the optic nerve nipple is located 3 mm nasally and 0.5 mm inferiorly. This structure and location of the disc contributes to the formation of a negative, absolute, physiological scotoma in the upper-temporal part of our field of vision, referred to in ophthalmology as a blind spot. The optic nerve fibers, located where the optic disc and retina are located, lack myelin. The total intrabulbar path in millimeters is slightly more than 0.5.

Intraorbital department

Immediately in the area behind the cribriform plate of the sclera, the nerve fibers acquire a myelin sheath, which then continues throughout the rest of the optic nerve. The diameter of the nerve behind the sclera increases from 3.5 mm to 4–4.5 mm. This happens due to the fact that the structure of the nerve undergoes changes - three sheaths are attached to it from the outside, surrounding the nerve trunk on all sides. The arachnoid, hard and soft membranes are connected on the one hand with the membranes located in the brain in the corresponding sections, and on the other with the sclera.

The hard (outer) shell of the optic nerve merges with the sclera at the eyeball. Its anatomy is represented by coarse collagen fibers with an admixture of elastic fibers. The thickness of the hard shell is greatest; the inside is lined with endothelium, separated by a fascial layer from the fatty tissue of the orbit. Where hard shell completely merges with the sclera, the optic nerve is equipped along the circumference with trunks and vessels of the ciliary nerves, the course of which goes through the sclera and ends inside the eye.

The pia surrounds the nerve trunk and is separated from it by the glial mantle, which is a thin layer of glia. The soft shell is in close connection with the nerve trunk itself and sends inside it a large number of connective tissue partitions of the first and second order, called septa. The functions of these septa are to divide the optic nerve into separate bundles. The septa also enhance the strength of the optic nerve, perhaps due to the fact that their anatomy consists of elastic tissue, collagen and glia, which in turn penetrate the nerve fascicles.

The course of the vessels involved in supplying power to the optic nerve trunk is limited by its septa. The vessels do not go inside the nerve bundles, so the nutrition of individual nerve fibers is carried out by glia. The endothelium covers the outside of the soft membrane. In front, the soft shell gradually passes into the cribriform plate, sending a certain amount of its fibers to the choroid. Pathological accumulation of fluid in this area leads to compression soft fabric optic nerve, resulting in swelling of the optic nerve nipple.

The arachnoid membrane is located in the space between the hard and soft membranes of the nerve. Its structure is tender and loose, and its function divides the intervaginal space into subarachnoid and subdural. In the subarachnoid space there are beams consisting of elastic and collagen fibrils, which are lined with endothelium.

The course of the central retinal artery begins outside the optic nerve at the level of its inferior side. The artery at a distance of 7–12 mm from the eyeball has an arcuate bend, after which it enters the trunk of the optic nerve at a right angle and is then located along its axis. Throughout the entire length of the nerve, the artery is enveloped in a connective tissue membrane called the “central connective tissue cord.” The function of this sheath is protective - it protects the nerve fibers from the effects of the pulse wave.

The optic nerve in the eye orbit makes an S-shaped bend. Due to this, the entire length of the optic nerve increases. This length makes the eyeball mobile, and in addition, protects the optic fibers from injury and tension when the eyeball makes large and sharp movements in different directions. The length of the intraorbital nerve can range from 25 to 35 mm.

Intracanalicular section

The dura mater at the nerve in the bone canal connects to the periosteum. The optic nerve canal in this place has the narrowest interstitial space. The length of the intracanalicular area can be from 5 to 8 mm.

Intracranial section

The shape of the intracranial section is ovoid and somewhat flattened, the length is short. The left and right optic nerves move closer to each other. As a result, a chiasma is formed. The chiasma is covered by the arachnoid and soft shells, it is located in the sella turcica (on its diaphragm). The visual tracts located posterior to the chiasm are referred to as the optic tract.

Visual pathways and their role in the visual analyzer

Where the visual pathway connects the retina and the cortical center of the visual analyzer, there are two neurons, designated as central and peripheral. The peripheral neuron pathway begins from the axons of ganglion cells located in the retina. The peripheral neuron ends in the structure of the external geniculate body. The peripheral neuron is divided into three parts of the visual pathway, these include the chiasm, optic tract and optic nerve.

The central neuron starts from the lateral geniculate body, more precisely from its nerve cells. At its origin, the central neuron forms the so-called Graziole bundle; it passes through the internal capsule and ends in the brain - the cortex of its occipital lobe in the area of the calcarine groove.

The optic nerve forms the initial part of the visual pathways. The axons of ganglion cells located in the retina come in the form of bundles of nerves and have a specific location in the optic nerve trunk. The order of arrangement corresponds to the parts of the retina from which they originate.

Fibers originating in the upper retina pass to the dorsal, superior side of the optic nerve. The fibers of the lower sector occupy its ventral, that is, bottom part. The same correspondence exists in the inner and outer sectors of the optic nerve and retina.

The papillomacular bundle starts from the macular region, which is considered one of the most functionally important. This bundle is located in the nerve disc in its temporal sector. The beam occupies 2/5 of the cross section. The bundle retains its peripheral location only in the anterior section of the nerve; as it moves away from the eye, it somewhat modifies its shape. In the orbital region, its posterior part, the papillomacular bundle shifts to the central part of the optic nerve and then runs along its axis. Central position the bundle ends at the place where the chiasm is located.

Chiasm - optic chiasm. The nerve fibers emerging from the nasal portions of the retina undergo complete decussation. The fibers pass to the opposite section in the medial part of the retina. Laterally located fibers do not intersect with the temporal side and remain on it. Similarly, incomplete decussation is detected in the papillomacular bundle. Chiasmus exposed pathological processes, leads to the development of bitemporal hemianopsia.

The visual pathways located behind the chiasm are referred to as the optic tract. Due to the semi-crossing of nerve fibers, the right optic tract includes fibers from the right parts of the retina. When it is destroyed, the left halves of the visual field fall out and left-sided homonymous hemianopsia develops. The left optic tract is connected to the left parts of both retinas. If the conduction of the left tract is disrupted, the right visual fields fall out and right-sided hemianopsia occurs.

Blood supply to the optic nerve

The ophthalmic artery is predominantly involved in the blood supply to the optic nerve. The ophthalmic artery arises from the fifth flexure of the internal carotid artery. The course of the ophthalmic artery has several branches, which next to the optic nerve in front are directed to eyeball, and behind – to the bone canal. The blood supply to the optic nerve is also provided by larger arteries, which include the lacrimal artery, posterior ciliary artery and central retinal artery.