A person sees not with his eyes, but through his eyes, from where information is transmitted through the optic nerve, chiasm, visual tracts to certain areas of the occipital lobes of the cerebral cortex, where the picture of the external world that we see is formed. All these organs make up our visual analyzer or visual system.

Having two eyes allows us to make our vision stereoscopic (that is, form a three-dimensional image). The right side of the retina in each eye transmits the “right side” of the image to the right side of the brain via the optic nerve, and the left side of the retina acts similarly. Then the brain connects two parts of the image - right and left - together.

Since each eye perceives “its own” picture, if the joint movement of the right and left eyes is disrupted, binocular vision may be disrupted. Simply put, you will begin to see double or see two completely different pictures at the same time.

Basic functions of the eye

• optical system that projects the image;
• a system that perceives and “encodes” the received information for the brain;
• "serving" life support system.

The eye can be called a complex optical device. Its main task is to “transmit” the correct image to the optic nerve.

Cornea- a transparent membrane covering the front of the eye. It lacks blood vessels and has great refractive power. Part of the optical system of the eye. The cornea borders the opaque outer layer of the eye, the sclera. See structure of the cornea.

Anterior chamber of the eye- This is the space between the cornea and the iris. It is filled with intraocular fluid.

Iris- shaped like a circle with a hole inside (pupil). The iris consists of muscles that, when contracted and relaxed, change the size of the pupil. It enters the choroid of the eye. The iris is responsible for the color of the eyes (if it is blue, it means there are few pigment cells, if it is brown, it means a lot). Performs the same function as the aperture in a camera, regulating the light flow.

Pupil- a hole in the iris. Its size usually depends on the light level. The more light, the smaller the pupil.

Lens- the “natural lens” of the eye. It is transparent, elastic - it can change its shape, almost instantly “focusing”, due to which a person sees well both near and far. Located in the capsule, held ciliary girdle. The lens, like the cornea, is part of the optical system of the eye.

Vitreous body - a gel-like transparent substance located in the back of the eye. The vitreous maintains its shape eyeball, participates in intraocular metabolism. Part of the optical system of the eye.

Retina- consists of photoreceptors (they are sensitive to light) and nerve cells. Receptor cells located in the retina are divided into two types: cones and rods. In these cells, which produce the enzyme rhodopsin, the energy of light (photons) is converted into electrical energy in nervous tissue, i.e. a photochemical reaction.

Rods are highly photosensitivity and allow you to see in low light; they are also responsible for peripheral vision. Cones, on the contrary, require more light for their work, but they allow you to see small details (responsible for central vision) and make it possible to distinguish colors. The largest concentration of cones is located in the central fossa (macula), which is responsible for the highest visual acuity. The retina is adjacent to the choroid, but in many areas it is loose. This is where it tends to flake off when various diseases retina.

Sclera- the opaque outer layer of the eyeball, which in front of the eyeball turns into a transparent cornea. 6 extraocular muscles are attached to the sclera. It contains a small amount nerve endings and vessels.

Choroid— lines the posterior part of the sclera, the retina is adjacent to it, with which it is closely connected. The choroid is responsible for the blood supply to intraocular structures. In diseases of the retina, it is very often involved in the pathological process. There are no nerve endings in the choroid, so when it is diseased, there is no pain, which usually signals some kind of problem.

Optic nerve- with help optic nerve signals from nerve endings are transmitted to the brain.

The human organ of vision is almost no different in structure from the eyes of other mammals, which means that during the process of evolution the structure of the human eye has not undergone significant changes. And today the eye can rightfully be called one of the most complex and high-precision devices, created by nature for the human body. You will learn more about how the human visual apparatus works, what the eye consists of and how it works in this review.

General information about the structure and operation of the organ of vision

The anatomy of the eye includes its external (visually visible from the outside) and internal (located inside the skull) structure. The outer part of the eye, accessible to observation, includes the following bodies:

• Eye socket;
• Eyelid;
• Lacrimal glands;
• Conjunctiva;
• Cornea;
• Sclera;
• Iris;
• Pupil.

From the outside, the eye looks like a slit on the face, but in fact the eyeball has the shape of a ball, slightly elongated from the forehead to the back of the head (in the sagittal direction) and having a mass of about 7 g. Elongation of the anteroposterior size of the eye more than normal leads to myopia, and shortening - to farsightedness.

Eyelids, tear glands and eyelashes

These organs do not belong to the structure of the eye, but without them normal visual function is impossible, so they are also worth considering. The job of the eyelids is to moisturize the eyes, remove debris from them and protect them from damage.

Regular moistening of the surface of the eyeball occurs when blinking. On average, a person blinks 15 times per minute, less often when reading or working with a computer. The lacrimal glands, located in the upper outer corners of the eyelids, work continuously, secreting the liquid of the same name into the conjunctival sac. Excess tears are removed from the eyes through the nasal cavity, entering it through special tubules. In a pathology called dacryocystitis, the corner of the eye cannot communicate with the nose due to blockage of the lacrimal canal.

The inner side of the eyelid and the front visible surface of the eyeball are covered with the thinnest transparent membrane - the conjunctiva. It also contains additional small lacrimal glands.

It is its inflammation or damage that causes us to feel sand in the eye.

The eyelid maintains a semicircular shape thanks to the inner dense cartilaginous layer and the circular muscles - the palpebral fissure closures. The edges of the eyelids are decorated with 1-2 rows of eyelashes - they protect the eyes from dust and sweat. Here the excretory ducts of small sebaceous glands open, the inflammation of which is called barley.

Oculomotor muscles

These muscles work more actively than all other muscles of the human body and serve to give direction to the gaze. Strabismus occurs due to inconsistency in the work of the muscles of the right and left eyes. Special muscles move the eyelids - raise and lower them. Oculomotor muscles are attached by their tendons to the surface of the sclera.

Optical system of the eye

Let's try to imagine what's inside the eyeball. The optical structure of the eye consists of light refractive, accommodative and receptor apparatuses. Below is short description the entire path traveled by a light ray entering the eye. The structure of the eyeball in cross-section and the passage of light rays through it will be presented to you by the following drawing with symbols.

Cornea

The first eye “lens” onto which a ray reflected from an object hits and is refracted is the cornea. This is what covers the entire optical mechanism of the eye on the front side.

It provides a wide field of vision and clarity of the image on the retina.

Damage to the cornea leads to tunnel vision - a person sees the world around him as if through a pipe. The eye “breathes” through the cornea - it allows oxygen to pass through from the outside.

Properties of the cornea:

• Lack of blood vessels;
• Full transparency;
• High sensitivity to external influences.

The spherical surface of the cornea preliminarily collects all rays into one point, so that project it onto the retina. Various microscopes and cameras have been created in the likeness of this natural optical mechanism.

Iris with pupil

Some of the rays passing through the cornea are filtered out by the iris. The latter is delimited from the cornea by a small cavity filled with a transparent chamber fluid - the anterior chamber.

The iris is a movable light-proof diaphragm that regulates the passing light flow. The round colored iris is located just behind the cornea.

Its color varies from light blue to dark brown and depends on the race of the person and heredity.

Sometimes there are people whose left and right eye have different colors. Albinos have a red iris.

R
the iris is equipped blood vessels and is equipped with special muscles - circular and radial. The first (sphincters), contracting, automatically narrow the lumen of the pupil, and the second (dilators), contracting, expand it if necessary.

The pupil is located in the center of the iris and is a round hole with a diameter of 2–8 mm. Its narrowing and expansion occurs involuntarily and is in no way controlled by a person. By narrowing in the sun, the pupil protects the retina from burns. In addition to bright light, the pupil narrows from irritation of the trigeminal nerve and from certain medications. Pupil dilation can occur from strong negative emotions (horror, pain, anger).

Lens

Then the light flux hits a biconvex elastic lens - the lens. It is an accommodative mechanism located behind the pupil and delimits the anterior section of the eyeball, including the cornea, iris and anterior chamber of the eye. The vitreous body is tightly adjacent to it at the back.

The transparent protein substance of the lens lacks blood vessels and innervation. The organ substance is enclosed in a dense capsule. The lens capsule is radially attached to the ciliary body of the eye using the so-called ciliary girdle. Tension or loosening of this band changes the curvature of the lens, which allows you to clearly see both close and distant objects. This property is called accommodation.

The thickness of the lens varies from 3 to 6 mm, the diameter depends on age, reaching 1 cm in an adult. For newborns and infancy The lens is characterized by an almost spherical shape due to its small diameter, but as the child grows older, the diameter of the lens gradually increases. In older people, the accommodative functions of the eyes deteriorate.

Pathological clouding of the lens is called cataract.

Vitreous body

The vitreous body fills the cavity between the lens and the retina. Its composition is represented by a transparent gelatinous substance that freely transmits light. With age, as well as with high and moderate myopia, small opacities appear in the vitreous body, perceived by a person as “flying spots”. The vitreous body lacks blood vessels and nerves.

Retina and optic nerve

After passing through the cornea, pupil and lens, the light rays are focused on the retina. The retina is the inner layer of the eye, characterized by the complexity of its structure and consisting mainly of nerve cells. It is a part of the brain that has grown forward.

The light-sensitive elements of the retina have the form of cones and rods. The former are the organ of daytime vision, and the latter are the organ of twilight vision.

Rods are capable of perceiving very weak light signals.

A deficiency in the body of vitamin A, which is part of the visual substance of the rods, leads to night blindness - a person has difficulty seeing at dusk.

The optic nerve, which is a group of nerve fibers connected together and emanating from the retina, originates from the cells of the retina. The location where the optic nerve enters the retina is called the blind spot. since it does not contain photoreceptors. The area with the largest number of light-sensitive cells is located above the blind spot, approximately opposite the pupil, and is called the “Yellow Spot”.

The human organs of vision are designed in such a way that on their way to the cerebral hemispheres, some of the fibers of the optic nerves of the left and right eyes intersect. Therefore, in each of the two hemispheres of the brain there are nerve fibers from both the right and left eyes. The point where the optic nerves cross is called the chiasma. The picture below indicates the location of the chiasm - the base of the brain.

The construction of the path of the light flux is such that the object being viewed by a person is displayed upside down on the retina.

After this, the image is transmitted to the brain using the optic nerve, which “turns” it to its normal position. The retina and optic nerve are the receptor apparatus of the eye.

The eye is one of the most perfect and complex creations of nature. The slightest disturbance in at least one of its systems leads to visual impairment.

Videos that may be of interest to you:

Optic tract and optic chiasm.

Eyeball

The eyeball itself is located in the socket, and is surrounded on the outside by protective soft tissues(muscle fibers, fatty tissue, nerve pathways). In front, the eyeball is covered with eyelids and the conjunctival membrane, which protect the eye.

The apple has three shells that divide the space inside the eye into the anterior and posterior chambers, as well as the vitreous chamber. The latter is completely filled with vitreous humor.

Fibrous (outer) layer of the eye

The outer shell consists of fairly dense connective tissue fibers. In its anterior section, the shell is presented, which has a transparent structure, and throughout the rest of it it is white in color and has an opaque consistency. Due to elasticity and elasticity, both of these shells create the shape of the eye.

Cornea

The cornea makes up about a fifth of the fibrous membrane. It is transparent, and at the point of transition to the opaque sclera it forms a limbus. The shape of the cornea is usually an ellipse, the dimensions of which in diameter are 11 and 12 mm, respectively. The thickness of this transparent shell is 1 mm. Due to the fact that all the cells in this layer are strictly oriented in the optical direction, this shell is completely transparent to light rays. In addition, the absence of blood vessels in it also plays a role.

The layers of the cornea can be divided into five, similar in structure:

• Anterior epithelial layer.
• Bowman's shell.
• Corneal stroma.
• Descemet's membrane.
• The posterior epithelial layer, called endothelium.

The cornea contains a large number of nerve receptors and endings, and therefore it is very sensitive to external influences. Due to the fact that it is transparent, the cornea allows light to pass through. However, at the same time, it refracts it, since it has enormous refractive power.

Sclera

The sclera refers to the opaque part of the outer fibrous membrane of the eye and has a white tint. The thickness of this layer is only 1 mm, but it is very strong and dense, as it consists of special fibers. A number of extraocular muscles are attached to it.

Choroid

The choroid is considered medium, and its composition mainly includes various vessels. It consists of three main components:

• The iris, which is located in front.
• Ciliary (ciliary) body, belonging to the middle layer.
• Actually, which is the back part.

The shape of this layer resembles a circle, inside of which there is a hole called the pupil. It also contains two orbicularis muscles, which provide optimal pupil diameter in different lighting conditions. In addition, it contains pigment cells that determine eye color. If there is little pigment, then the eye color is blue, if there is a lot, then brown. The main function of the iris is to regulate the thickness of the light flux, which passes into the deeper layers of the eyeball.

The pupil is an opening inside the iris, the size of which is determined by the amount of light in the external environment. The brighter the lighting, the narrower the pupil, and vice versa. The average pupil diameter is about 3-4 mm.

Choroid

The choroid is represented by the posterior region of the choroid and consists of veins, arteries and capillaries. Its main task is to deliver nutrients to the iris and ciliary body. Due to the large number of vessels, it has a red color and stains the fundus of the eye.

Retina

The reticular inner shell is the first section that belongs to the visual analyzer. It is in this shell that light waves are transformed into nerve impulses, disseminating information to central structures. In the brain centers, the received impulses are processed and an image is created that is perceived by a person. The composition includes six layers of different fabrics.

The outer layer is pigmented. Due to the presence of pigment, it scatters light and absorbs it. The second layer consists of processes of retinal cells (cones and rods). These processes contain a large amount of rhodopsin (c) and iodopsin (c).

The most active part of the retina (optical) is visualized during fundus examination and is called the fundus. This area contains a large number of vessels, the optic disc, which corresponds to the exit of nerve fibers from the eye, and the macula. The latter is a special area of ​​the retina in which the largest number of cones are located, which determine daytime color vision.

The apple has three shells that divide the space inside the eye into the anterior and posterior chambers, as well as the vitreous chamber.

Inner nucleus of the eye

Aqueous moisture

The intraocular fluid is located in the anterior chamber of the eye, surrounded by the cornea and iris, as well as in the posterior chamber, formed by the iris and lens. These cavities communicate with each other through the pupil, so fluid can move freely between them. The composition of this moisture is similar to blood plasma; its main role is nutritional (for the cornea and lens).

Lens

The lens is an important organ of the optical system, which consists of a semi-solid substance and does not contain blood vessels. It is presented in the form of a biconvex lens, on the outside of which there is a capsule. Lens diameter 9-10 mm, thickness 3.6-5 mm.

The lens is located in the recess behind the iris on the anterior surface of the vitreous body. The stability of the position is ensured by fixation using the ligaments of Zinn. From the outside, the lens is washed by intraocular fluid, which nourishes it with various useful substances. The main role of the lens is refractive. Due to this, it promotes rays directly on the retina.

Vitreous body

In the posterior part of the eye, the vitreous body is localized, which is a gelatinous transparent mass similar in consistency to a gel. The volume of this chamber is 4 ml. The main component of the gel is water, as well as hyaluronic acid(2%). In the area of ​​the vitreous body, fluid constantly moves, which allows nutrition to be delivered to the cells. Among the functions of the vitreous body it is worth noting: refractive, nourishing (for the retina), as well as maintaining the shape and tone of the eyeball.

Eye protective apparatus

Eye socket

The orbit is part of the skull and is the container for the eye. Its shape resembles a tetrahedral truncated pyramid, the top of which is directed inward (at an angle of 45 degrees). The base of the pyramid faces outward. The dimensions of the pyramid are 4 by 3.5 cm, and the depth reaches 4-5 cm. In the cavity of the orbit, in addition to the eyeball itself, there are muscles, choroid plexuses, a fatty body, and the optic nerve.

Eyelids

The upper and lower eyelids help protect the eye from external influences (dust, foreign particles, etc.). Due to the high sensitivity, when the cornea is touched, the eyelids immediately close tightly. Due to blinking movements, small foreign objects and dust are removed from the surface of the cornea, and tear fluid is distributed. During closure, the edges of the upper and lower eyelids are very tightly adjacent to each other, and additionally located along the edge. The latter also help protect the eyeball from dust.

The skin in the eyelid area is very delicate and thin, it gathers into folds. Under it there are several muscles: the levator of the upper eyelid and the orbicularis, which ensures rapid closure. The conjunctival membrane is located on the inner surface of the eyelids.

Conjunctiva

The conjunctival membrane has a thickness of about 0.1 mm and is represented by mucosal cells. It covers the eyelids, forms the fornix of the conjunctival sac, and then passes to the anterior surface of the eyeball. The conjunctiva ends at the limbus. If you close your eyelids, this mucous membrane forms a cavity that has the shape of a bag. With open eyelids, the volume of the cavity is significantly reduced. The function of the conjunctiva is primarily protective.

Lacrimal apparatus of the eye

The lacrimal apparatus includes the gland, canaliculi, lacrimal puncta and sac, as well as the nasolacrimal duct. The lacrimal gland is located in the area of ​​the upper outer wall of the orbit. It secretes tear fluid, which penetrates through the channels into the eye area, and then into the lower conjunctival fornix.

After this, a tear through the lacrimal puncta located in the area of ​​the inner corner of the eye, along tear ducts enters the lacrimal sac. The latter is located between the inner corner of the eyeball and the wing of the nose. From the bag, tears can flow through the nasolacrimal duct directly into the nasal cavity.

The tear itself is a rather salty, transparent liquid that has a slightly alkaline environment. A person produces about 1 ml of such liquid with a varied biochemical composition per day. The main functions of tears are protective, optical, and nutritional.

Muscular apparatus of the eye

The muscular system of the eye includes six extraocular muscles: two oblique, four rectus. There is also the levator superioris and the orbicularis oculi muscle. All these muscle fibers ensure the movement of the eyeball in all directions and the squinting of the eyelids.

The organ of vision (visual analyzer) consists of 4 parts: 1) the peripheral, or perceptive, part - the eyeball with appendages; 2) pathways - the optic nerve, consisting of axons of ganglion cells, chiasm, optic tract; 3) subcortical centers - external geniculate bodies, optic radiance, or Graziole's radiate fascicle; 4) higher visual centers in the occipital lobes of the cerebral cortex.

The peripheral part of the organ of vision includes the eyeball, the protective apparatus of the eyeball (orbit and eyelids) and the adnexal apparatus of the eye (lacrimal and motor apparatus).

The eyeball consists of different tissues, which are anatomically and functionally divided into 4 groups: 1) the visual-nervous apparatus, represented by the retina with its conductors to the brain; 2) choroid - choroid, ciliary body and iris; 3) a light-refracting (dioptric) apparatus, consisting of the cornea, aqueous humor, lens and vitreous body; 4) the outer capsule of the eye - the sclera and cornea.

The visual process begins in the retina, which interacts with the choroid, where light energy is converted into nerve stimulation. The remaining parts of the eye are essentially auxiliary.

They create best conditions for the act of seeing. An important role is played by the diopter apparatus of the eye, with the help of which a clear image of objects in the outside world is obtained on the retina.

The external muscles (4 rectus and 2 obliques) make the eye extremely mobile, which ensures the rapid direction of the gaze to the object that currently attracts attention.

All other auxiliary organs of the eye have a protective significance. The orbit and eyelids protect the eye from adverse external influences. The eyelids also help moisturize the cornea and drain tears. The lacrimal apparatus produces tear fluid, which moisturizes the cornea, washes away small debris from its surface and has a bactericidal effect.

External structure

To describe the external structure of the human eye, you can use the following picture:

Here you can highlight the eyelids (upper and lower), eyelashes, the inner corner of the eye with the lacrimal caruncle (fold of the mucous membrane), the white part of the eyeball - the sclera, which is covered with a transparent mucous membrane - the conjunctiva, the transparent part - the cornea, through which the round pupil and iris (individually colored, with a unique pattern). The junction of the sclera and the cornea is called the limbus.

The eyeball has an irregular spherical shape, anterior-posterior size for an adult, it is about 23-24 mm.

The eyes are located in a bony container - the eye sockets. On the outside they are protected by eyelids, the edges of the eyeballs are surrounded oculomotor muscles and fatty tissue. The optic nerve leaves the inside of the eye and goes through a special canal into the cranial cavity, reaching the brain.
Eyelids

The eyelids (upper and lower) are covered on the outside with skin, on the inside with mucous membrane (conjunctiva). In the thickness of the eyelids there are cartilages, muscles (the orbicularis oculi muscle and the muscle that lifts the upper eyelid) and glands. The eyelid glands produce components of the eye's tears, which normally wet the surface of the eye. On the free edge of the eyelids, eyelashes grow, which perform a protective function, and gland ducts open. Between the edges of the eyelids there is a palpebral fissure. In the inner corner of the eye, on the upper and lower eyelids, there are lacrimal puncta - openings through which tears flow through the nasolacrimal duct into the nasal cavity.

Muscles of the eye

There are 8 muscles in the orbit. Of these, 6 move the eyeball: 4 straight - upper, lower, internal and external (mm. recti superior, et inferior, extemus, interims), 2 oblique - upper and lower (mm. obliquus superior et inferior); the muscle that lifts the upper eyelid (t. levator palpebrae), and the orbital muscle (t. orbitalis). The muscles (except for the orbital and inferior oblique) originate deep in the orbit and form a common tendon ring (annulus tendineus communis Zinni) at the apex of the orbit around the optic nerve canal. The tendon fibers intertwine with the hard sheath of the nerve and pass onto the fibrous plate that covers the superior orbital fissure.

Eye shells

The human eyeball has 3 membranes: outer, middle and inner.

Outer lining of the eyeball

The outer shell of the eyeball (3rd shell): an opaque sclera or tunica albuginea and a smaller one - a transparent cornea, along the edge of which there is a translucent rim - the limbus (1-1.5 mm wide).

Sclera

The sclera (tunika fibrosa) is an opaque, dense fibrous part of the outer membrane of the eye, poor in cellular elements and blood vessels, occupying 5/6 of its circumference. It is white or slightly bluish in color and is sometimes called the tunica albuginea. The radius of curvature of the sclera is 11 mm; on top it is covered with a suprascleral plate - episclera, consisting of its own substance and an inner layer that has a brownish tint (brown sclera plate). The structure of the sclera is close to collagen tissues, since it consists of intercellular collagen formations, thin elastic fibers and a substance that glues them together. Between the inner part of the sclera and the choroid there is a gap - the suprachoroidal space. The outside of the sclera is covered with episclera, to which it is connected by loose connective tissue fibers. The episclera is the inner wall of Tenon's space.
In front, the sclera passes into the cornea, this place is called the limbus. Here is one of the thinnest places of the outer shell, since it is thinned by the structures of the drainage system, the intrascleral outflow tracts.

Cornea

The density and low pliability of the cornea ensure that the shape of the eye is maintained. Rays of light penetrate the eye through the transparent cornea. It has an ellipsoidal shape with a vertical diameter of 11 mm and a horizontal diameter of 12 mm, the average radius of curvature is 8 mm. The thickness of the cornea at the periphery is 1.2 mm, in the center up to 0.8 mm. The anterior ciliary arteries give off branches that go to the cornea and form a dense network of capillaries along the limbus - the marginal vascular network of the cornea.

The vessels do not enter the cornea. It is also the main refractive medium of the eye. The lack of external permanent protection of the cornea is compensated by the abundance of sensory nerves, as a result of which the slightest touch to the cornea causes convulsive closure of the eyelids, a feeling of pain and a reflex increase in blinking with lacrimation

The cornea has several layers and is covered on the outside with a precorneal film, which plays a critical role in preserving the function of the cornea and preventing keratinization of the epithelium. Precorneal fluid moisturizes the surface of the epithelium of the cornea and conjunctiva and has a complex composition, including the secretion of a number of glands: the main and accessory lacrimal, meibomian, glandular cells of the conjunctiva.

Choroid

The choroid (2nd layer of the eye) has a number of structural features, which causes difficulties in determining the etiology of diseases and treatment.
The posterior short ciliary arteries (6-8 in number), passing through the sclera around the optic nerve, break up into small branches, forming the choroid.
The posterior long ciliary arteries (2 in number), having penetrated the eyeball, run anteriorly in the suprachoroidal space (in the horizontal meridian) and form a large arterial circle of the iris. The anterior ciliary arteries, which are a continuation of the muscular branches of the ophthalmic artery, also participate in its formation.
The muscular branches supplying blood to the rectus oculi muscles run forward towards the cornea called the anterior ciliary arteries. A little short of reaching the cornea, they go inside the eyeball, where, together with the posterior long ciliary arteries, they form a large arterial circle of the iris.

The choroid has two blood supply systems - one for the choroid (system of the posterior short ciliary arteries), the other for the iris and ciliary body (system of the posterior long and anterior ciliary arteries).

The choroid consists of the iris, ciliary body and choroid. Each department has its own purpose.

Choroid

The choroid makes up the posterior 2/3 of the vascular tract. Its color is dark brown or black, which depends on the large number of chromatophores, the protoplasm of which is rich in the brown granular pigment melanin. The large amount of blood contained in the vessels of the choroid is associated with its main trophic function - to ensure the restoration of constantly decaying visual substances, due to which the photochemical process is maintained at a constant level. Where the optically active part of the retina ends, the choroid also changes its structure and the choroid turns into the ciliary body. The border between them coincides with the jagged line.

Iris

The anterior part of the vascular tract of the eyeball is the iris; in its center there is a hole - the pupil, which acts as a diaphragm. The pupil regulates the amount of light entering the eye. The diameter of the pupil is changed by two muscles located in the iris - the constrictor and dilator of the pupil. From the fusion of the long posterior and anterior short vessels of the choroid, it arises big circle blood circulation of the ciliary body, from which vessels extend radially into the iris. An atypical course of vessels (not radial) may be either a variant of the norm, or, more importantly, a sign of neovascularization, reflecting chronic (at least 3-4 months) inflammatory process in the eye. New formation of blood vessels in the iris is called rubeosis.

Ciliary body

The ciliary, or ciliary, body has the shape of a ring with the greatest thickness at the junction with the iris due to the presence of smooth muscle. The participation of the ciliary body in the act of accommodation, which provides clear vision at various distances, is associated with this muscle. The ciliary processes produce intraocular fluid, which ensures constant intraocular pressure and delivers nutrients to the avascular structures of the eye - the cornea, lens and vitreous body.

Lens

The second most powerful refractive medium of the eye is the lens. It has the shape of a biconvex lens, is elastic, and transparent.

The lens is located behind the pupil; it is a biological lens, which, under the influence of the ciliary muscle, changes the curvature and participates in the act of accommodation of the eye (focusing the gaze on objects at different distances). The refractive power of this lens varies from 20 diopters at rest to 30 diopters when the ciliary muscle is working.

The space behind the lens is filled with a vitreous body, which contains 98% water, some protein and salts. Despite this composition, it does not blur, as it has a fibrous structure and is enclosed in a thin shell. The vitreous body is transparent. Compared to other parts of the eye, it has the largest volume and mass of 4 g, and the mass of the entire eye is 7 g

Retina

The retina is the innermost (1st) layer of the eyeball. This is the initial peripheral section visual analyzer. Here the energy of light rays is converted into the process of nervous excitation and the primary analysis of optical stimuli entering the eye begins.

The retina has the appearance of a thin transparent film, the thickness of which is 0.4 mm near the optic nerve, 0.1-0.08 mm at the posterior pole of the eye (in the macula), and 0.1 mm at the periphery. The retina is fixed in only two places: at the optic disc due to optic nerve fibers, which are formed by processes of retinal ganglion cells, and at the dentate line (ora serrata), where the optically active part of the retina ends.

Ora serrata has the appearance of a jagged, zigzag line located in front of the equator of the eye, approximately 7-8 mm from the corneoscleral border, corresponding to the attachment sites of the external muscles of the eye. Throughout the rest of the retina, the retina is held in place by the pressure of the vitreous body, as well as the physiological connection between the ends of the rods and cones and the protoplasmic processes of the pigment epithelium, so retinal detachment and a sharp decrease in vision are possible.

The pigment epithelium, genetically related to the retina, is anatomically closely related to the choroid. Together with the retina, the pigment epithelium participates in the act of vision, since it forms and contains visual substances. Its cells also contain a dark pigment - fuscin. By absorbing beams of light, the pigment epithelium eliminates the possibility of diffuse light scattering within the eye, which could reduce the clarity of vision. The pigment epithelium also promotes the renewal of rods and cones.
The retina consists of 3 neurons, each of which forms an independent layer. The first neuron is represented by receptor neuroepithelium (rods and cones and their nuclei), the second by bipolar cells, and the third by ganglion cells. There are synapses between the first and second, second and third neurons.

according to: E.I. Sidorenko, Sh.Kh. Jamirze “Anatomy of the organ of vision”, Moscow, 2002

Undoubtedly, each of the senses is important and necessary for a person to fully perceive the world around him.

Vision allows people to see the world as it is - bright, diverse, unique.

Organ - vision

In the human organ - vision - we can distinguish the following components:

• The peripheral zone is responsible for the correct perception of the initial data. In turn, it is divided into:
  • eyeball;
  • protection system;
  • adnexal system;
  • motor system.
• The area responsible for conducting nerve signals.
• Subcortical centers.
• Cortical visual centers.

Anatomy of the human eye structure

The eyeball looks like a ball. Its location is concentrated in the orbit, which has high strength due to bone tissue. Eyeball from bone formation separated by a fibrous membrane. The motor activity of the eye is carried out thanks to the muscles.

Outer shell of the eye presented connective tissue. The anterior zone is called the cornea and has a transparent structure. The posterior zone is the sclera, better known as the protein. Thanks to the outer shell, the shape of the eye is round.

Cornea. A small part of the outer layer. The shape resembles an ellipse, the dimensions of which are as follows: horizontal - 12 mm, vertical - 11 mm. The thickness of this part of the eye does not exceed one millimeter. A distinctive feature of the cornea is the complete absence of blood vessels. The cells of the cornea form a clear order, which is what makes it possible to see the picture undistorted and clear. The cornea is a convex-concave lens with a refractive power of approximately forty diopters. The sensitivity of this area of ​​the fibrous layer is very significant. This is explained by the fact that the zone is the location of nerve endings.

Sclera (protein). It is opaque and durable. The composition includes fibers that have an elastic structure. The muscles of the eye are attached to the protein.

Middle layer of the eye. It is represented by blood vessels and is divided by ophthalmologists into the following zones:

• iris;
• ciliary body or ciliary body;
• choroid.

Iris. A circle in the center of which, in a special hole, the pupil is located. The muscles located inside the iris allow the pupil to change in diameter. This happens when they contract and relax. It is important to note that the designated zone determines the shade of human eyes.

Ciliary or ciliary body. Location: central zone of the middle ocular membrane. Outwardly it looks like a circular roller. The structure is slightly thickened.

The vascular part of the eye - processes, carry out the formation of ocular fluid. Special ligaments attached to the vessels, in turn, fix the lens.

Choroid. Posterior zone of the medial shell. It is represented by arteries and veins, with their help the other parts of the eye are supplied with food.

Inner lining of the eye– retina. The thinnest of all three shells. Presented different types cells: rods and cones.

It should be noted that peripheral and twilight vision in humans is possible due to the fact that rods are present in the shell and have high photosensitivity.

Cones are responsible for central vision. In addition, thanks to cones, a person has the ability to distinguish colors. The maximum concentration of these cells occurs in the macula or corpus luteum. The main function of this zone is to ensure visual acuity.

Ocular nucleus (eye cavity). The core consists of the following components:

• fluid that fills the chambers of the eye;
• lens;
• vitreous body.

The anterior chamber is located between the iris and cornea. The cavity between the lens and the iris is the posterior chamber. The two cavities have the ability to interact using the pupil. Thanks to this, intraocular fluid easily circulates between the two cavities.

Lens. One of the components of the ocular nucleus. Located in a transparent capsule, the location of which is the anterior zone of the vitreous body. Externally similar to a biconvex lens. Nutrition is carried out through the intraocular fluid. Ophthalmology identifies several important components of the lens:

• capsule;
• capsular epithelium;
• lens substance.

Over the entire surface, the lens and vitreous body are separated from each other by a thin layer of liquid.

Vitreous body. Occupies the largest part of the eye. The consistency resembles a gel. Main components: water and hyaluronic acid. Provides nutrition to the retina and is part of the optical system of the eye. The vitreous body consists of three components:

• the vitreous body itself;
• limiting membrane;
• Klyuev channel.

In this video you will see the principle of the human eye.

Eye protection system

Eye socket. A niche formed by bone tissue where the eye is directly located. In addition to the eyeball, it consists of:

• optic nerves;
• vessels;
• fat;
• muscles.

Eyelids. Folds formed by skin. The main task is to protect the eyes. Thanks to the eyelids, the eye is protected from mechanical damage and foreign bodies. In addition, the eyelids distribute intraocular fluid over the entire surface of the eye. The skin of the eyelids is very thin. The conjunctiva is located along the entire surface of the eyelids on the inner side.

Conjunctiva. Mucous membrane of the eyelids. Location: anterior zone of the eye. Gradually transforms into conjunctival sacs without affecting the cornea of ​​the eye. In the closed position of the eyes, with the help of the conjunctival leaves, a hollow space is formed, protecting against drying out and mechanical damage.

Lacrimal system of the eye

Includes several components:

• lacrimal gland;
• lacrimal sac;
• nasolacrimal duct.

The lacrimal gland is located near the outer edge of the orbit, in the upper zone. The main function is the synthesis of tear fluid. Subsequently, the fluid follows the excretory ducts and, washing outer surface eyes, accumulates in the conjunctival sac. At the last stage, fluid is collected in the lacrimal sac.

Muscular apparatus of the eye

The rectus and oblique muscles cause eye movement. The muscles originate in the orbit. Following along the entire eye, the muscles end in the white.

In addition, this system contains muscles that allow the eyelids to close and open - the levator palpebral muscle and the orbicularis or orbital muscle.

Photo of the structure of the human eye

A diagram and drawing of the structure of the human eye can be seen in these pictures: