The name of the part of the eye is the structure of the function. Diagram of the structure and principle of operation of the human eye

The human organ of vision almost does not differ in its structure from the eyes of other mammals, which means that in the process of evolution the structure of the human eye has not undergone significant changes. And today the eye can rightly 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 that can be seen includes the following bodies:

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

Outwardly, 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 (along the sagittal direction) and having a mass of about 7 g. farsightedness.

Eyelids, lacrimal glands and eyelashes

These organs do not belong to the structure of the eye, but normal visual function is impossible without them, so they should also be considered. The job of the eyelids is to moisten the eyes, remove debris from them and protect them from injury.

Regular moistening of the surface of the eyeball occurs when blinking. On average, a person blinks 15 times per minute, while reading or working with a computer - less often. The lacrimal glands, located in the upper outer corners of the eyelids, work continuously, releasing the fluid 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 is 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 keeps a semicircular shape due to the internal dense cartilaginous layer and circular muscles - palpebral fissures. 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 the 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. From the inconsistency in the work of the muscles of the right and left eyes, strabismus occurs. Special muscles set the eyelids in motion - raise and lower them. oculomotor muscles are attached with their tendons to the surface of the sclera.

Optical system of the eye

Let's try to imagine what is inside the eyeball. The optical structure of the eye consists of refractive, accommodative and receptor apparatus.. The following is a brief description of the entire path traveled by a light beam entering the eye. The device of the eyeball in section and the passage of light rays through it will present you with the following figure with symbols.

Cornea

The first eye "lens" on which the beam reflected from the object falls and is refracted is the cornea. This is what the entire optical mechanism of the eye is covered on the front side.

It is she who provides an extensive field of view 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. Through the cornea of ​​​​the eye "breathes" - it passes oxygen from the outside.

Cornea properties:

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

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

Iris with pupil

Some of the rays that pass 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 opaque diaphragm that regulates the flow of light passing through. 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 on heredity.

Sometimes there are people who have left and right eye have a different color. The red color of the iris occurs in albinos.

R
the arcuate membrane is supplied with blood vessels and is equipped with special muscles - annular 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 not controlled by a person in any way. By narrowing in the sun, the pupil protects the retina from burns. Except from bright light, the pupil constricts from irritation of the trigeminal nerve and from certain medications. Pupil dilation can occur from strong negative emotions (horror, pain, anger).

lens

Further, the light flux enters a biconvex elastic lens - the lens. It is an accommodation mechanism located behind the pupil and delimits the anterior part of the eyeball, including the cornea, iris and anterior chamber of the eye. Behind it tightly adjoins the vitreous body.

In the transparent protein substance of the lens, there are no blood vessels and innervation. The substance of the organ is enclosed in a dense capsule. The lens capsule is radially attached to the ciliary body of the eye. with the help of the so-called ciliary girdle. Tensioning or loosening 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. Newborns and infants are characterized by an almost spherical shape of the lens 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 a 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 medium myopia, small opacities appear in the vitreous body, perceived by a person as “flying flies”. 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 shell 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 are in the form of cones and rods. The first are the organ of daytime vision, and the second - twilight.

Rods are able to perceive very weak light signals.

Deficiency in the body of vitamin A, which is part of the visual substance of the rods, leads to night blindness - a person does not see well at dusk.

From the cells of the retina originates the optic nerve, which is connected together nerve fibers emanating from the retina. The place where the optic nerve enters the retina is called the blind spot. since it does not contain photoreceptors. The zone with the largest number of photosensitive cells is located above the blind spot, approximately opposite the pupil, and is called the Yellow Spot.

The human organs of vision are arranged in such a way that on their way to the hemispheres of the brain, part 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 of both the right and left eyes. The point where the optic nerves cross is called the chiasma. The picture below shows the location of the chiasm, the base of the brain.

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

After that, the image is transmitted with the help of the optic nerve to the brain, "turning" it into a 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 disturbances.

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The structure of the human eye includes many complex systems that make up the visual system, which provides information about what surrounds a person. The sense organs included in it, characterized as paired, are distinguished by the complexity of the structure and uniqueness. Each of us has individual eyes. Their features are exceptional. At the same time, the structure of the human eye and its functionality have common features.

Evolutionary development has led to the fact that the organs of vision have become the most complex formations at the level of structures of tissue origin. The main purpose of the eye is to provide vision. This possibility is guaranteed by blood vessels, connective tissues, nerves and pigment cells. Below is a description of the anatomy and main functions of the eye with symbols.

Under the scheme of the structure of the human eye, one should understand the entire eye apparatus having an optical system responsible for processing information in the form of visual images. This implies its perception, subsequent processing and transmission. All this is realized due to the elements that form the eyeball.

The eyes are rounded. Its location is a special recess in the skull. It is referred to as the eye. The outer part is closed with eyelids and folds of skin that serve to accommodate muscles and eyelashes.

• moisturizing, which is provided by the glands in the eyelashes. The secretory cells of this species contribute to the formation of the corresponding fluid and mucus;
• protection against mechanical damage. This is achieved by closing the eyelids;
• removal of the smallest particles falling on the sclera.

The functioning of the vision system is configured in such a way as to transmit the received light waves with maximum accuracy. In this case, a careful attitude is required. The sense organs in question are fragile.

Eyelids

Skin folds are what the eyelids are, which are constantly in motion. Flashing occurs. This possibility is available due to the presence of ligaments located along the edges of the eyelids. Also, these formations act as connecting elements. With their help, the eyelids are attached to the eye socket. The skin forms the top layer of the eyelids. Then comes the muscle layer. Next comes cartilage and conjunctiva.

The eyelids in the part of the outer edge have two ribs, where one is anterior and the other is posterior. They form an intermarginal space. The ducts from the meibomian glands exit here. With their help, a secret is developed that makes it possible to slide the eyelids with the utmost ease. At the same time, the density of closing of the eyelids is achieved, and conditions are created for the correct removal of the lacrimal fluid.

On the front rib there are bulbs that provide the growth of cilia. The ducts that serve as transport routes for the oily secret also come out here. Here are the conclusions of the sweat glands. The angles of the eyelids correspond with the findings of the lacrimal ducts. The back rib ensures that each eyelid fits snugly against the eyeball.

The eyelids are characterized by complex systems that provide these organs with blood and maintain the correct conduction of nerve impulses. The carotid artery is responsible for blood supply. Regulation at the level of the nervous system - the involvement of motor fibers that form the facial nerve, as well as providing appropriate sensitivity.

The main functions of the eyelid include protection against damage as a result of mechanical impact and foreign bodies. To this should be added the moisturizing function, which contributes to the saturation of the internal tissues of the organs of vision with moisture.

The eye socket and its contents

The bony cavity refers to the orbit, which is also referred to as the bony orbit. It serves as reliable protection. The structure of this formation includes four parts - upper, lower, outer and inner. They form a single whole due to a stable connection with each other. However, their strength is different.

The outer wall is especially reliable. The internal one is much weaker. Blunt traumas can provoke its destruction.

• inside - a lattice labyrinth;
• bottom - maxillary sinus;
• top - frontal emptiness.

Such structuring creates a certain danger. Tumor processes that develop in the sinuses can spread to the cavity of the orbit. The reverse action is also allowed. The eye socket communicates with the cranial cavity through a large number of holes, which suggests the possibility of inflammation moving to areas of the brain.

Pupil

The pupil of the eye is a round hole located in the center of the iris. Its diameter can be changed, which allows you to adjust the degree of penetration of the light flux into the inner region of the eye. The muscles of the pupil in the form of a sphincter and a dilator provide the conditions when the illumination of the retina changes. Activation of the sphincter constricts the pupil, and the dilator dilates it.

Such functioning of the mentioned muscles is akin to how the diaphragm of a camera works. Blinding light leads to a decrease in its diameter, which cuts off too intense light rays. Conditions are created when image quality is achieved. Lack of illumination leads to a different result. The diaphragm expands. The quality of the picture again remains high. Here we can talk about the diaphragm function. With its help, the pupillary reflex is provided.

The size of the pupils is adjusted automatically, if such an expression is acceptable. Human consciousness does not explicitly control this process. The manifestation of the pupillary reflex is associated with a change in the illumination of the retina. Absorption of photons starts the process of transmission of the relevant information, where addressees are understood as nerve centers. The required sphincter response is achieved after signal processing by the nervous system. Its parasympathetic department comes into action. As for the dilator, the sympathetic department comes into play here.

Pupil reflexes

The reaction in the form of a reflex is provided by sensitivity and excitation of motor activity. First, a signal is formed as a response to a certain impact, and the nervous system comes into play. This is followed by a specific reaction to the stimulus. Muscle tissues are included in the work.

Lighting causes the pupil to constrict. This cuts off blinding light, which has a positive effect on the quality of vision.

• straight - one eye is illuminated. He reacts as required;
• friendly - the second organ of vision is not illuminated, but responds to the light effect exerted on the first eye. The effect of this type is achieved by the fact that the fibers of the nervous system are partially crossed. Chiasma is formed.

The stimulus in the form of light is not the only reason for the change in the diameter of the pupils. Still possible are such moments as convergence - stimulation of the activity of the rectus muscles of the visual organ, and - the involvement of the ciliary muscle.

The appearance of the considered pupillary reflexes occurs when the point of stabilization of vision changes: the gaze is transferred from an object located at a great distance to an object located at a closer distance. The proprioreceptors of the mentioned muscles are activated, which is provided by the fibers going to the eyeball.

Emotional stress, such as pain or fear, stimulates pupil dilation. If the trigeminal nerve is irritated, and this indicates low excitability, then a narrowing effect is observed. Also, similar reactions occur when taking certain drugs that excite the receptors of the corresponding muscles.

optic nerve

The functionality of the optic nerve is to deliver the appropriate messages to certain areas of the brain designed to process light information.

Light pulses first hit the retina. The location of the visual center is determined by the occipital lobe of the brain. The structure of the optic nerve suggests the presence of several components.

At the stage of intrauterine development, the structures of the brain, the inner shell of the eye and the optic nerve are identical. This gives grounds to assert that the latter is a part of the brain that is outside the cranium. At the same time, ordinary cranial nerves have a different structure from it.

The optic nerve is short. It is 4–6 cm. It is mainly located behind the eyeball, where it is immersed in the fat cell of the orbit, which guarantees protection from damage from the outside. The eyeball in the part of the posterior pole is the site where the nerve of this species begins. In this place, there is an accumulation of nerve processes. They form a kind of disk (OND). This name is due to the flattened shape. Moving on, the nerve enters the orbit with subsequent immersion in the meninges. It then reaches the anterior cranial fossa.

The optic pathways form a chiasm within the skull. They intersect. This feature is important in diagnosing eye and neurological diseases.

Directly below the chiasm is the pituitary gland. How effectively the endocrine system is able to work depends on its condition. Such anatomy is clearly visible if the tumor processes affect the pituitary gland. Opto-chiasmal syndrome becomes the board of pathology of this type.

The internal branches of the carotid artery are responsible for supplying blood to the optic nerve. The insufficient length of the ciliary arteries excludes the possibility of a good blood supply to the optic disc. At the same time, other parts receive blood in full.

The processing of light information directly depends on the optic nerve. Its main function is to deliver messages regarding the received picture to specific recipients in the form of the corresponding areas of the brain. Any injury to this formation, regardless of severity, can lead to negative consequences.

eyeball chambers

Closed-type spaces in the eyeball are the so-called chambers. They contain intraocular moisture. There is a connection between them. There are two such formations. One is in the front position, and the other is in the back. The pupil acts as a link.

The anterior space is located just behind the corneal region. Its back side is limited by the iris. As for the space behind the iris, this is the rear chamber. The vitreous body serves as its support. The unchanging volume of chambers is the norm. The production of moisture and its outflow are processes that contribute to the adjustment of compliance with standard volumes. The production of eye fluid is possible due to the functionality of the ciliary processes. Its outflow is provided by a drainage system. It is located in the frontal part, where the cornea is in contact with the sclera.

The functionality of the chambers is to maintain "cooperation" between the intraocular tissues. They are also responsible for the flow of light fluxes to the retina. The rays of light at the entrance are refracted accordingly as a result of joint activity with the cornea. This is achieved through the properties of optics, inherent not only in the moisture inside the eye, but also in the cornea. Creates a lens effect.

The cornea, in part of its endothelial layer, acts as an external limiter for the anterior chamber. The border of the reverse side is formed by the iris and lens. The maximum depth falls on the area where the pupil is located. Its value reaches 3.5 mm. When moving to the periphery, this parameter slowly decreases. Sometimes this depth is greater, for example, in the absence of the lens due to its removal, or less if the choroid exfoliates.

The posterior space is limited in front by the leaf of the iris, and its back rests against the vitreous body. The equator of the lens acts as an internal limiter. The outer barrier forms the ciliary body. Inside there is a large number of zinn ligaments, which are thin threads. They create a formation that acts as a link between the ciliary body and the biological lens in the form of a lens. The shape of the latter is able to change under the influence of the ciliary muscle and the corresponding ligaments. This provides the required visibility of objects, regardless of their distance.

The composition of the moisture inside the eye correlates with the characteristics of the blood plasma. The intraocular fluid makes it possible to deliver the nutrients required to ensure the normal functioning of the organs of vision. Also with its help the possibility of removal of products of an exchange is realized.

The capacity of the chambers is determined by volumes in the range from 1.2 to 1.32 cm3. In this case, it is important how the production and outflow of eye fluid is performed. These processes require balance. Any disruption in the operation of such a system leads to negative consequences. For example, there is a possibility of development, which threatens with serious problems with the quality of vision.

The ciliary processes serve as sources of eye moisture, which is achieved by filtering the blood. The immediate place where the fluid is formed is the posterior chamber. After that, it moves to the anterior with a subsequent outflow. The possibility of this process is determined by the difference in pressure created in the veins. At the last stage, moisture is absorbed by these vessels.

Schlemm's channel

The gap inside the sclera, characterized as circular. Named after the German physician Friedrich Schlemm. The anterior chamber, in part of its angle, where the junction of the iris and cornea is formed, is a more precise area for the location of the Schlemm's canal. Its purpose is to remove aqueous humor with its subsequent absorption by the anterior ciliary vein.

The structure of the channel is more related to how the lymphatic vessel looks. Its inner part, which comes into contact with the generated moisture, is a mesh formation.

The channel's liquid transport capacity is 2 to 3 micro liters per minute. Injuries and infections block the channel, which provokes the appearance of a disease in the form of glaucoma.

Blood supply to the eye

Creating a flow of blood to the organs of vision is the functionality of the ophthalmic artery, which is an integral part of the structure of the eye. A corresponding branch is formed from the carotid artery. It reaches the eye opening and penetrates the orbit, which it does along with the optic nerve. Then its direction changes. The nerve bends around from the outside in such a way that the branch is on top. An arc is formed with muscular, ciliary and other branches emanating from it. The central artery provides blood supply to the retina. The vessels involved in this process form their own system. It also includes the ciliary arteries.

After the system is in the eyeball, it is divided into branches, which guarantees proper nutrition of the retina. Such formations are defined as terminal: they do not have connections with adjacent vessels.

Ciliary arteries are characterized by location. The posterior ones reach the back of the eyeball, bypass the sclera and diverge. The features of the front include the fact that they differ in length.

The ciliary arteries, defined as short, pass through the sclera and form a separate vascular formation consisting of many branches. At the entrance to the sclera, a vascular corolla is formed from the arteries of this type. It occurs where the optic nerve originates.

Ciliary arteries of smaller length also end up in the eyeball and rush to the ciliary body. In the frontal region, each such vessel splits into two trunks. A formation with a concentric structure is created. After which they meet with similar branches of another artery. A circle is formed, defined as a large arterial. A similar formation of smaller sizes also occurs in the place where the ciliary and pupillary iris belt is located.

The ciliary arteries, characterized as anterior, are part of the muscular blood vessels of this type. They do not end in the area formed by the rectus muscles, but stretch further. There is an immersion in the episcleral tissue. First, the arteries pass along the periphery of the eyeball, and then go deep into it through seven branches. As a result, they connect with each other. A circle of blood circulation is formed along the perimeter of the iris, designated as a large one.

On the approach to the eyeball, a loopy network is formed, consisting of ciliary arteries. She entangles the cornea. There is also a division of non-branches that provide blood supply to the conjunctiva.

Partially, the outflow of blood is facilitated by the veins that go along with the arteries. This is mainly possible due to the venous pathways, which are collected in separate systems.

Whirlpool veins serve as a kind of collectors. Their function is to collect blood. The passage of these veins of the sclera occurs at an oblique angle. They provide blood flow. She enters the eye socket. The main collector of blood is the ophthalmic vein, which occupies the upper position. Through the corresponding gap, it is displayed in the cavernous sinus.

The ophthalmic vein below receives blood from the whirlpool veins passing in this place. It is splitting up. One branch connects to the ophthalmic vein located above, and the other reaches the deep vein of the face and the slit-like space with the pterygoid process.

Basically, the blood flow from the ciliary veins (anterior) fills such vessels of the orbit. As a result, the main volume of blood enters the venous sinuses. A reverse flow is created. The remaining blood moves forward and fills the veins of the face.

The orbital veins connect with the veins of the nasal cavity, facial vessels, and the ethmoid sinus. The largest anastomosis is formed by the veins of the orbit and face. Its border affects the inner corner of the eyelids and directly connects the ophthalmic vein and the facial vein.

Muscles of the eye

The possibility of good and three-dimensional vision is achieved when the eyeballs are able to move in a certain way. Here, the coordination of the work of the visual organs is of particular importance. The guarantors of this functioning are six muscles of the eye, where four of them are straight, and two are oblique. The latter are so called because of the peculiarity of the course.

The cranial nerves are responsible for the activity of these muscles. The fibers of the considered group of muscle tissue are maximally saturated with nerve endings, which determines their work from a position of high accuracy.

Through the muscles responsible for the physical activity of the eyeballs, diverse movements are available. The need to implement this functionality is determined by the fact that the coordinated work of this type of muscle fibers is required. The same pictures of objects should be fixed on the same areas of the retina. This allows you to feel the depth of space and see perfectly.

The structure of the muscles of the eye

The muscles of the eye begin near the ring, which serves as the environment of the optic canal close to the external opening. The only exception concerns oblique muscle tissue, which occupies the lower position.

The muscles are arranged so that they form a funnel. Nerve fibers and blood vessels pass through it. As you move away from the beginning of this formation, the oblique muscle located at the top deviates. There is a shift towards a kind of block. Here it is transformed into a tendon. Passing through the block loop sets the direction at an angle. The muscle is attached to the upper iris of the eyeball. The oblique muscle (lower) also begins there, from the edge of the orbit.

As the muscles approach the eyeball, a dense capsule (Tenon's membrane) is formed. A connection is established with the sclera, which occurs with varying degrees of distance from the limbus. At the minimum distance, the internal rectus muscle is located, at the maximum distance, the upper one. The oblique muscles are fixed closer to the center of the eyeball.

The function of the oculomotor nerve is to maintain the proper functioning of the muscles of the eye. The responsibility of the abducens nerve is determined by maintaining the activity of the rectus muscle (external), and the trochlear - by the superior oblique. The regulation of this type is characterized by its own peculiarity. The control of a small number of muscle fibers is carried out due to one branch of the motor nerve, which significantly increases the clarity of eye movements.

The nuances of muscle attachment set the variability of exactly how the eyeballs are able to move. The rectus muscles (internal, external) are attached in such a way that they are provided with horizontal rotations. The activity of the internal rectus muscle allows you to turn the eyeball towards the nose, and the external one - to the temple.

The rectus muscles are responsible for vertical movements. There is a nuance to their location, due to the fact that there is a certain slope of the fixation line, if you focus on the limbus line. This circumstance creates conditions when, together with the vertical movement, the eyeball turns inward.

The functioning of the oblique muscles is more complex. This is explained by the peculiarities of the location of this muscle tissue. Lowering the eye and turning outward is provided by the oblique muscle located at the top, and lifting, including turning outward, is also an oblique muscle, but already lower.

Another of the capabilities of the muscles mentioned is the provision of minor rotations of the eyeball in accordance with the movement of the clock hand, regardless of direction. Regulation at the level of maintaining the desired activity of nerve fibers and the coherence of the work of the eye muscles are two points that contribute to the implementation of complex turns of the eyeballs of any direction. As a result, vision acquires such a property as volume, and its clarity increases significantly.

Shells of the eye

The shape of the eye is held by the appropriate shells. Although the functionality of these formations is not limited to this. With their help, the delivery of nutrients is carried out, and the process is supported (clear vision of objects when the distance to them changes).

• fibrous;
• vascular;
• retina.

Fibrous membrane of the eye

Connective tissue that allows you to hold a specific shape of the eye. It also acts as a protective barrier. The structure of the fibrous membrane suggests the presence of two components, where one is the cornea, and the second is the sclera.

Cornea

A shell characterized by transparency and elasticity. The shape corresponds to a convex-concave lens. The functionality is almost identical to what a camera lens does: it focuses rays of light. The concave side of the cornea looks back.

• epithelium;
• Bowman's membrane;
• stroma;
• Descemet's membrane;
• endothelium.

Sclera

The external protection of the eyeball plays an important role in the structure of the eye. Forms a fibrous membrane, which also includes the cornea. Unlike the latter, the sclera is an opaque tissue. This is due to the chaotic arrangement of collagen fibers.

The main function is high-quality vision, which is guaranteed due to the obstruction of the penetration of light rays through the sclera.

The possibility of blindness is excluded. Also, this formation serves as a support for the components of the eye, which are placed outside the eyeball. These include nerves, vessels, ligaments and oculomotor muscles. The density of the structure ensures the maintenance of intraocular pressure within the specified values. The helmet canal acts as a transport channel that provides an outflow of eye moisture.

choroid

• iris;
• ciliary body;
• choroid.

iris

Part of the choroid, which differs from other departments of this formation in that its location is frontal versus parietal, if you focus on the plane of the limbus. Represents a disk. In the center is a hole known as the pupil.

• border, located in front;
• stromal;
• pigment-muscular.

Fibroblasts are involved in the formation of the first layer, connecting with each other through their processes. Behind them are pigment-containing melanocytes. The color of the iris depends on the number of these specific skin cells. This trait is inherited. The brown iris is dominant in terms of inheritance, and the blue iris is recessive.

In the bulk of newborns, the iris has a light blue tint, which is due to poorly developed pigmentation. Closer to six months of age, the color becomes darker. This is due to an increase in the number of melanocytes. The absence of melanosomes in albinos leads to the dominance of pink. In some cases, it is possible when the eyes in the part of the iris get a different color. Melanocytes are capable of provoking the development of melanomas.

Further immersion in the stroma reveals a network consisting of a large number of capillaries and collagen fibers. The distribution of the latter captures the muscles of the iris. There is a connection with the ciliary body.

The back layer of the iris consists of two muscles. The pupillary sphincter, shaped like a ring, and the dilator, which has a radial orientation. The functioning of the first is provided by the oculomotor nerve, and the second - by the sympathetic. The pigment epithelium is also present here as part of an undifferentiated area of ​​the retina.

The thickness of the iris varies depending on the specific area of ​​this formation. The range of such changes is 0.2–0.4 mm. The minimum thickness is observed in the root zone.

The center of the iris is occupied by the pupil. Its width is changeable under the influence of light, which is provided by the corresponding muscles. High illumination provokes contraction, and less illumination provokes expansion.

The iris in part of its anterior surface is divided into pupillary and ciliary zones. The width of the first is 1 mm and the second - from 3 to 4 mm. The distinction in this case provides a kind of roller, which has a toothed shape. The muscles of the pupil are distributed as follows: the sphincter is the pupillary belt, and the dilator is the ciliary.

The ciliary arteries, which form a large arterial circle, deliver blood to the iris. The small arterial circle also participates in this process. The innervation of this particular zone of the choroid is achieved by the ciliary nerves.

ciliary body

The area of ​​the choroid responsible for the production of eye fluid. The name ciliary body is also used.
The structure of the formation in question is muscle tissue and blood vessels. The muscular content of this shell suggests the presence of several layers with different directions. Their activity includes the work of the lens. Its form is changing. As a result, a person gets the opportunity to clearly see objects at different distances. Another functionality of the ciliary body is to retain heat.

The blood capillaries located in the ciliary processes contribute to the production of intraocular moisture. Blood flow is filtered. Moisture of this kind ensures the proper functioning of the eye. The intraocular pressure is kept constant.

Also, the ciliary body serves as a support for the iris.

Choroidea (Choroidea)

The area of ​​the vascular tract, located behind. The limits of this shell are limited to the optic nerve and the dentate line.
The parameter thickness of the posterior pole is from 0.22 to 0.3 mm. When approaching the dentate line, it decreases to 0.1–0.15 mm. The choroid in part of the vessels consists of ciliary arteries, where the posterior short ones go towards the equator, and the anterior ones go towards the choroid, when the connection of the second with the first is achieved in its anterior region.

The ciliary arteries bypass the sclera and reach the suprachoroidal space bounded by the choroid and sclera. There is a disintegration into a significant number of branches. They become the basis of the choroid. The vascular circle of Zinn-Galera is formed along the perimeter of the optic disc. Sometimes there may be an additional branch in the macula. It is visible either on the retina or on the optic disc. An important point in embolism of the central retinal artery.

• supravascular with dark pigment;
• vascular brownish hue;
• vascular-capillary, supporting the work of the retina;
• basal layer.

The retina of the eye (retina)

The retina is a peripheral section that launches the visual analyzer, which plays an important role in the structure of the human eye. With its help, light waves are captured, they are converted into impulses at the level of excitation of the nervous system, and further information is transmitted through the optic nerve.

The retina is the nerve tissue that forms the eyeball in part of its inner shell. It limits the space filled with the vitreous body. The choroid acts as an outer frame. The thickness of the retina is insignificant. The parameter corresponding to the norm is only 281 microns.

The surface of the eyeball from the inside is mostly covered with retina. The beginning of the retina can conditionally be considered the ONH. Further, it stretches to such a border as a jagged line. Then it is transformed into the pigment epithelium, envelops the inner shell of the ciliary body and spreads to the iris. The optic disc and the dentate line are areas where the attachment of the retina is most secure. In other places, its connection is characterized by low density. It is this fact that explains why the fabric peels off easily. This causes a lot of serious problems.

The structure of the retina is formed by several layers with different functionality and structure. They are closely connected to each other. A tight contact is formed, which determines the creation of what is commonly called a visual analyzer. Through it, a person is given the opportunity to correctly perceive the world around him, when an adequate assessment of the color, shape and size of objects, as well as the distance to them is made.

Rays of light, when they enter the eye, pass through several refractive media. Under them should be understood the cornea, eye fluid, the transparent body of the lens and the vitreous body. If the refraction is within the normal range, then as a result of such a passage of light rays, a picture of objects that fall into the field of view is formed on the retina. The resulting image differs in that it is inverted. Further, certain parts of the brain receive the appropriate impulses, and a person acquires the ability to see what surrounds him.

From the point of view of the structure of the retina - the most complex formation. All its components closely interact with each other. It is multi-layered. Damage to any layer can lead to a negative outcome. Visual perception as the functionality of the retina is provided by a three-neural network that conducts excitations from receptors. Its composition is formed by a wide set of neurons.

Retinal layers

Retina forms a "sandwich" of ten rows:

1. pigment epithelium adjacent to Bruch's membrane. Differs in wide functionality. Protection, cellular nutrition, transportation. It accepts the rejecting segments of photoreceptors. Serves as a barrier to light radiation.

2. photosensor layer. Cells that are sensitive to light, in the form of a kind of rods and cones. The rod-like cylinders contain the visual segment rhodopsin, and the cones contain iodopsin. The first provides color perception and peripheral vision, and the second provides vision in low light.

3. Boundary membrane(outer). Structurally, it consists of terminal formations and external sections of retinal receptors. The structure of Müller cells, through their processes, makes it possible to collect light on the retina and deliver it to the appropriate receptors.

4. nuclear layer(outer). It got its name due to the fact that it is formed on the basis of the nuclei and bodies of light-sensitive cells.

5. Plexiform layer(outer). Determined by contacts at the cell level. Occur between neurons characterized as bipolar and associative. This also includes light-sensitive formations of this type.

6. nuclear layer(interior). Formed from different cells, for example, bipolar and Müllerian. The demand for the latter is associated with the need to maintain the functions of the nervous tissue. Others are focused on signal processing from photoreceptors.

7. Plexiform layer(interior). Interlacing of nerve cells in part of their processes. Serves as a separator between the inner part of the retina, characterized as vascular, and the outer - avascular.

8. ganglion cells. Provide free penetration of light due to the lack of such a coating as myelin. They act as a bridge between light-sensitive cells and the optic nerve.

9. ganglion cell. Participates in the formation of the optic nerve.

10. Boundary membrane(internal). Retina coating on the inside. Consists of Muller cells.

Optical system of the eye

The quality of vision depends on the main parts of the human eye. The condition of the transmissive in the form of the cornea, retina and lens directly affects how a person will see: good or bad.

The cornea takes a greater part in the refraction of light rays. In this context, we can draw an analogy with the principle of operation of the camera. The diaphragm is the pupil. With its help, the flow of light rays is regulated, and the focal length sets the image quality.

Thanks to the lens, light rays fall on the "film". In our case, it should be understood as the retina.

The vitreous body and the moisture in the eye chambers also refract light rays, but to a much lesser extent. Although the state of these formations significantly affects the quality of vision. It can worsen with a decrease in the degree of transparency of moisture or the appearance of blood in it.

The correct perception of the surrounding world through the organs of vision assumes that the passage of light rays through all optical media leads to the formation on the retina of a reduced and inverted image, but real. The final processing of information from the visual receptors occurs in the brain regions. The occipital lobes are responsible for this.

lacrimal apparatus

Physiological system that provides the production of special moisture with its subsequent withdrawal into the nasal cavity. The organs of the lacrimal system are classified depending on the secretory department and the lacrimal apparatus. The peculiarity of the system lies in the pairing of its organs.

The job of the end section is to produce a tear. Its structure includes the lacrimal gland and additional formations of a similar kind. The first refers to the serous gland, which has a complex structure. It is divided into two parts (bottom, top), where the tendon of the muscle responsible for lifting the upper eyelid acts as a separating barrier. The area at the top in terms of size is as follows: 12 by 25 mm at 5 mm thick. Its location is determined by the wall of the orbit, which has an upward and outward orientation. This part includes the excretory tubules. Their number varies from 3 to 5. The output is carried out in the conjunctiva.

As for the lower part, it has a smaller size (11 by 8 mm) and a smaller thickness (2 mm). She has tubules, where some connect with the same formations of the upper part, while others are removed into the conjunctival sac.

The lacrimal gland is supplied with blood through the lacrimal artery, and the outflow is organized into the lacrimal vein. The trigeminal facial nerve acts as the initiator of the corresponding excitation of the nervous system. Sympathetic and parasympathetic nerve fibers are also connected to this process.

In a standard situation, only accessory glands work. Through their functionality, the production of tears in a volume of about 1 mm is ensured. This provides the required hydration. As for the main lacrimal gland, it comes into action when various kinds of irritants appear. These can be foreign bodies, too bright light, emotional outburst, etc.

The structure of the lacrimal division is based on formations that promote the movement of moisture. They are also responsible for its withdrawal. This functioning is provided by the lacrimal stream, lake, points, tubules, sac and nasolacrimal duct.

The mentioned points are perfectly visualized. Their location is determined by the inner corners of the eyelids. They are oriented towards the lacrimal lake and are in close contact with the conjunctiva. The establishment of a connection between the bag and the points is achieved through special tubules, reaching a length of 8-10 mm.

The location of the lacrimal sac is determined by the bony fossa located near the angle of the orbit. From the point of view of anatomy, this formation is a closed cavity of a cylindrical type. It is extended by 10 mm, and its width is 4 mm. On the surface of the bag there is an epithelium, which has a goblet glandulocyte in its composition. Blood inflow is provided by the ophthalmic artery, and the outflow is provided by small veins. Part of the sac below communicates with the nasolacrimal canal, which opens into the nasal cavity.

vitreous body

Gel-like substance. Fills the eyeball by 2/3. Differs in transparency. Consists of 99% water, which contains hyaluronic acid.

There is a notch in the front. It is attached to the lens. Otherwise, this formation is in contact with the retina in part of its membrane. The optic disc and the lens are related through the hyaloid canal. Structurally, the vitreous body is composed of collagen protein in the form of fibers. The existing gaps between them are filled with liquid. This explains that the formation in question is a gelatinous mass.

On the periphery are hyalocytes - cells that contribute to the formation of hyaluronic acid, proteins and collagens. They are also involved in the formation of protein structures known as hemidesmosomes. With their help, a tight connection is established between the retinal membrane and the vitreous body itself.

• giving the eye a specific shape;
• refraction of light rays;
• creation of a certain tension in the tissues of the organ of vision;
• achieving the effect of incompressibility of the eye.

Photoreceptors

The type of neurons that make up the retina of the eye. Provide processing of the light signal in such a way that it is converted into electrical impulses. This triggers biological processes that lead to the formation of visual images. In practice, photoreceptor proteins absorb photons, which saturate the cell with the appropriate potential.

Light-sensitive formations are peculiar rods and cones. Their functionality contributes to the correct perception of objects of the external world. As a result, we can talk about the formation of the corresponding effect - vision. A person is able to see due to the biological processes occurring in such parts of the photoreceptors as the outer lobes of their membranes.

There are also light-sensitive cells known as the eyes of Hesse. They are located inside the pigment cell, which has a cup-shaped shape. The work of these formations is to capture the direction of the rays of light and determine its intensity. With their help, the light signal is processed when electrical impulses are obtained at the output.

The next class of photoreceptors became known in the 1990s. It refers to the light-sensitive cells of the ganglionic layer of the retina. They support the visual process, but in an indirect way. This refers to biological rhythms during the day and the pupillary reflex.

The so-called rods and cones differ significantly from each other in terms of functionality. For example, the first is characterized by high sensitivity. If the lighting is low, then it is they who guarantee the formation of at least some kind of visual image. This fact makes it clear why colors are poorly distinguished in low light. In this case, only one type of photoreceptors, rods, is active.

The cones need brighter light to work, to allow the appropriate biological signals to pass through. The structure of the retina suggests the presence of different types of cones. There are three in total. Each defines photoreceptors tuned to a particular wavelength of light.

For the perception of a picture in color, the cortical regions are responsible for the processing of visual information, which implies the recognition of impulses in the RGB format. Cones are able to distinguish light flux by wavelength, characterizing them as short, medium and long. Depending on how many photons the cone is able to absorb, corresponding biological reactions are formed. The various responses of these formations are based on a specific number of photons of one or another length taken in. In particular, the photoreceptor proteins of L-cones absorb the conventional red color associated with long wavelengths. Light rays of shorter length are capable of producing the same response if they are bright enough.

The reaction of the same photoreceptor can be provoked by light waves of different lengths, when differences are also observed at the intensity level of the light flux. As a result, the brain does not always determine the light and the resulting image. Through the visual receptors, the selection and selection of the brightest rays occurs. Then, biosignals are formed that enter those parts of the brain where information of this type is processed. A subjective perception of the optical image in color is created.

The human retina consists of 6 million cones and 120 million rods. In animals, their number and ratio is different. The main influence is the lifestyle. In owls, the retina contains a very significant number of rods. The human visual system is almost 1.5 million ganglion cells. Among them there are cells with photosensitivity.

lens

A biological lens characterized in terms of shape as biconvex. It acts as an element of the light-conducting and light-refracting system. Provides the ability to focus on objects at different distances. Located in the posterior chamber of the eye. The height of the lens is 8 to 9 mm and its thickness is 4 to 5 mm. With age, it thickens. This process is slow but sure. The anterior part of this transparent body has a less convex surface than the posterior one.

The shape of the lens corresponds to a biconvex lens having a radius of curvature in the anterior part of about 10 mm. At the same time, on the reverse side, this parameter does not exceed 6 mm. The lens diameter is 10 mm, and the size in the anterior part is from 3.5 to 5 mm. The substance contained inside is held by a thin-walled capsule. The front part has epithelial tissue located below. There is no epithelium on the back side of the capsule.

Epithelial cells differ in that they are constantly dividing, but this does not affect the volume of the lens in terms of its change. This situation is explained by the dehydration of old cells located at a minimum distance from the center of the transparent body. This helps to reduce their volume. The process of this type leads to such features as age. When a person reaches the age of 40, the elasticity of the lens is lost. The accommodation reserve is reduced, and the ability to see well at close range is significantly worsened.

The lens is located directly behind the iris. Its retention is provided by thin threads that form a zinn ligament. One of their ends enters the lens shell, and the other is fixed on the ciliary body. The degree of tension of these threads affects the shape of the transparent body, which changes the refractive power. As a result, the process of accommodation becomes possible. The lens serves as the boundary between two sections: anterior and posterior.

• light transmission - achieved due to the fact that the body of this element of the eye is transparent;
• light refraction - works like a biological lens, acts as a second refractive medium (the first is the cornea). At rest, the refractive power parameter is 19 diopters. This is the norm;
• accommodation - a change in the shape of a transparent body in order to have a good vision of objects located at different distances. The refractive power in this case varies in the range from 19 to 33 diopters;
• division - forms two sections of the eye (anterior, posterior), which is determined by the location. Acts as a barrier that holds back the vitreous body. It cannot be in the anterior chamber;
• protection - biological safety is ensured. Pathogenic microorganisms, once in the anterior chamber, are not able to penetrate the vitreous body.

Congenital diseases in some cases lead to displacement of the lens. It occupies the wrong position due to the fact that the ligamentous apparatus is weakened or has some structural defect. This also includes the likelihood of congenital opacities of the nucleus. All this contributes to a decrease in vision.

Zinn's bunch

Formation based on fibers, defined as glycoprotein and zonular. Provides fixation of the lens. The surface of the fibers is coated with a mucopolysaccharide gel, which is due to the need for protection from moisture present in the chambers of the eye. The space behind the lens serves as the place where this formation is located.

The activity of the ligament of zon leads to contraction of the ciliary muscle. The lens changes curvature, which allows you to focus on objects at different distances. Muscle tension loosens the tension, and the lens takes on a shape close to a ball. Relaxation of the muscle leads to tension in the fibers, which flattens the lens. Focus changes.

The considered fibers are divided into posterior and anterior. One side of the posterior fibers is attached at the serrated edge, and the other side is attached to the frontal region of the lens. The starting point of the anterior fibers is the base of the ciliary processes, and attachment is carried out in the back of the lens and closer to the equator. Crossed fibers contribute to the formation of a slit-like space along the periphery of the lens.

The fibers are attached to the ciliary body in part of the vitreous membrane. In the case of detachment of these formations, the so-called dislocation of the lens, due to its displacement, is ascertained.

The ligament of Zinn acts as the main element of the system that provides the possibility of accommodation of the eye.

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Eyeball

The eyeball is spherical in shape. It has anterior and posterior poles. The anterior pole is the most protruding point of the cornea, the posterior one is located from the exit point of the optic nerve. The conditional line connecting both poles is called the axis of the eye.

The eyeball consists of a core covered with three membranes: fibrous, vascular and internal, or reticular.

Outside, the eyeball is covered with a fibrous membrane, which is subdivided into the posterior section - the sclera and the transparent anterior - the cornea, the border between which runs along the scleral groove.

Behind the sclera is a cribriform plate through which the fibers of the optic nerve pass.

The cornea is a transparent convex saucer-shaped plate, consisting of five layers: anterior epithelium, anterior border plate, own substance (cornea), posterior border plate, posterior epithelium (corneal endothelium). The cornea is devoid of blood vessels, its nutrition occurs due to diffusion from the vessels of the limbus and the fluid of the anterior chamber of the eye.

Ahead, the choroid passes into a thickened ciliary body of an annular shape. The ciliary body is involved in the accommodation of the eye, supporting, fixing and stretching the lens. The ciliary body in front passes into the iris, which is a round disk with a hole in the center (pupil). The iris is located between the cornea and the lens.

The iris consists of five layers: the anterior - the epithelium - is a continuation of the epithelium covering the posterior surface of the cornea, followed by the outer boundary layer, the vascular layer, the inner boundary layer and the pigment layer lining the posterior surface.

The outer boundary layer is formed by the main substance, in which there are many fibroblasts and pigment cells. The vascular layer consists of loose fibrous connective tissue, which contains numerous vessels and pigment cells.

The inner (boundary) layer of the iris is similar in structure to the outer. The pigment layer of the iris is a continuation of the epithelium covering the ciliary body and ciliary processes, it is two-layered. The different quantity and quality of the melanin pigment determines the color of the eyes - brown, black (if there is a large amount of melanin), blue, greenish (if there is little pigment). The iris is 12 to 13 mm in diameter and about three-tenths of a millimeter thick. It has two circles - large and small.

The layers of the iris are as follows:

Endothelium

This layer is formed by complex cells that are responsible for contact with the aqueous humor (the fluid that is in the anterior part of the eye).

Stroma

This is the actual tissue of the iris of the eye, which consists of connective tissue, chromatic cells, muscle veins, nerve fibers, blood vessels, lymphatic vessels and a basilar membrane with a deep layer that contains a millimeter-wide annular border of muscle veins, the contraction of which reduces the size of the pupil ( sphincter).

Pigmentation layer

Consists of two rows of dark purple epithelial cells.

These are retinal epithelial cells that are located above the small circle of the iris and surround the pupil.

The innervation of the iris consists of a large neuroglandular autonomic system with sympathetic thoracolumbar regions and parasympathetic regions of the skull and pelvis.

The annular muscle fibers, as well as the ciliary muscle, are innervated by the section of the short ciliary nerve of the general motor system of the eye (III nerve), which is associated with the mesencephalic section.

The dilatory muscle fibers are innervated by the long ciliary nerve, which is associated with the sympathetic cervical ganglion.

These nerves pass to the iris through the layer of the shell of the eyeball, forming the iridological plexus, from where they are directed to muscle fibers and other structures of the iris. Some nerve fibers form a network, or chain, on the subendothelial surface. This chain consists of triangular cells whose bases describe concentric circles. Thus, there is a deep mobile chain of nerve fibers.

If we consider everything in a complex, then we can conclude that the iris is the most sensitive organ of the body: if the muscles of the legs correspond to 120 muscle fibers per unit, then the muscles of the iris correspond to from one to eight fibers per unit, which is a huge figure for such a small anatomical space.

The visual organs of fish are basically the same as those of other vertebrates. The mechanism of perception of visual sensations is similar to other vertebrates: light passes into the eye through the transparent cornea, then the pupil - a hole in the iris - passes it to the lens, and the lens transmits and focuses the light on the inner wall of the eye to the retina, where it is directly perceived. . The retina consists of light-sensitive (photoreceptor), nerve, as well as supporting cells.

Light-sensitive cells are located on the side of the pigment membrane. In their processes, shaped like rods and cones, there is a photosensitive pigment. The number of these photoreceptor cells is very large - there are 50 thousand of them per 1 mm 2 of the retina in carp (in squid - 162 thousand, spider - 16 thousand, human - 400 thousand, owl - 680 thousand). Through a complex system of contacts between the terminal branches of sensory cells and dendrites of nerve cells, light stimuli enter the optic nerve.

Cones in bright light perceive the details of objects and color. Rods perceive weak light, but they cannot create a detailed image.

The position and interaction of the cells of the pigment membrane, rods and cones change depending on the illumination. In the light, the pigment cells expand and cover the rods located near them; cones are drawn to the nuclei of cells and thus move towards the light. In the dark, sticks are drawn to the nuclei (and are closer to the surface); the cones approach the pigment layer, and the pigment cells reduced in the dark cover them.

The number of receptors of various kinds depends on the way of life of fish. In diurnal fish, cones prevail in the retina, in twilight and nocturnal fish, rods: burbot has 14 times more rods than pike. Deep-sea fish living in the darkness of the depths do not have cones, and the rods become larger and their number increases sharply - up to 25 million / mm 2 of the retina; the probability of capturing even weak light increases. Most fish distinguish colors, which is confirmed by the possibility of developing conditioned reflexes in them for a certain color - blue, green, red, yellow, blue.

Some deviations from the general scheme of the structure of the eye of a fish are associated with the characteristics of life in the water. The eye of the fish is elliptical. Among others, it has a silvery shell (between the vascular and protein), rich in guanine crystals, which gives the eye a greenish-golden sheen.

The cornea is almost flat (rather than convex), the lens is spherical (rather than biconvex) - this expands the field of view. The hole in the iris - the pupil - can change the diameter only within small limits. As a rule, fish do not have eyelids. Only sharks have a nictitating membrane that covers the eye like a curtain, and some herring and mullet have a fatty eyelid - a transparent film covering part of the eye.

The location of the eyes on the sides of the head (in most species) is the reason why fish have mostly monocular vision, and the ability for binocular vision is very limited. The spherical shape of the lens and moving it forward to the cornea provides a wide field of view: light enters the eye from all sides. The vertical angle of view is 150°, horizontally 168–170°. But at the same time, the sphericity of the lens causes myopia in fish. The range of their vision is limited and fluctuates due to the turbidity of the water from a few centimeters to several tens of meters.

Vision over long distances becomes possible due to the fact that the lens can be pulled back by a special muscle - a sickle-shaped process extending from the choroid of the bottom of the eyecup.

With the help of vision, fish are also guided by objects on the ground. Improved vision in the dark is achieved by the presence of a reflective layer (tapetum) - guanine crystals, underlain by pigment. This layer does not transmit light to the tissues lying behind the retina, but reflects it and returns it back to the retina. This increases the ability of the receptors to use the light that has entered the eye.

Due to habitat conditions, the eyes of fish can change greatly. In cave or abyssal (deep water) forms, the eyes can be reduced and even disappear. Some deep-sea fish, on the contrary, have huge eyes that allow them to capture very faint traces of light, or telescopic eyes, the collecting lenses of which the fish can put in parallel and acquire binocular vision. The eyes of some eels and larvae of a number of tropical fish are carried forward on long outgrowths (stalked eyes).

An unusual modification of the eyes of a four-eyed bird from Central and South America. Her eyes are placed on the top of her head, each of them is divided by a partition into two independent parts: the upper fish sees in the air, the lower - in the water. In the air, the eyes of fish crawling ashore or trees can function.

The role of vision as a source of information from the outside world for most fish is very large: when orienting during movement, when searching for and capturing food, while maintaining a flock, during the spawning period (the perception of defensive and aggressive postures and movements by rival males, and between individuals of different sexes - wedding attire and spawning "ceremonial"), in the relationship of the victim-predator, etc.

The ability of fish to perceive light has long been used in fishing (fishing by the light of a torch, fire, etc.).

It is known that fish of different species react differently to light of different intensities and different wavelengths, i.e., different colors. So, bright artificial light attracts some fish (Caspian sprat, saury, horse mackerel, mackerel, etc.) and scares away others (mullet, lamprey, eel, etc.). Different species are also selectively related to different colors and different light sources - surface and underwater. All this is the basis for the organization of industrial fishing for electric light (this is how sprat, saury and other fish are caught).

Vision gives a person a detailed image of the environment and allows you to navigate and act in it. The organ of vision is the eye. In the eye, light energy is converted into nerve impulse energy.

The eye is built according to the chamber type. It is shaped like a ball, sometimes called an eyeball.

Shells of the eye

The dense fibrous membrane, which, like a bag, contains all the internal elements, is called the sclera. The front of the sclera has a transparent area called the cornea.

Rice. 1. The structure of the eye.

Under the sclera is the choroid. It contains the blood vessels that feed the eye. In front of the eye, the choroid passes into the iris, which in the middle has a hole with a changing diameter - the pupil.

The third, inner shell is called the retina, it contains receptor cells.

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optical apparatus

The optical apparatus of the eye includes all transparent elements:

• cornea;
• anterior chamber fluid;
• lens;
• vitreous body.

The lens divides the eye into anterior and posterior chambers. It has the shape of a biconvex lens. By function, it is a lens that can change its curvature due to the contraction of the ciliary muscles.

It is impossible to see near and far objects at the same time. When viewing close objects, the lens becomes convex, and distant objects become flatter.

Rice. 2. Appearance of the eye.

Outside, the eye is periodically closed by two eyelids, which moisten the cornea with a tear secreted by the lacrimal gland.

Receptor apparatus

After passing through the vitreous body, light enters the retina. It consists of several layers of cells.

Rice. 3. Layers of the retina.

The retina contains rods and cones - 2 types of photoreceptors.

Sticks:

• perceive twilight light;
• more numerous;
• give night, black and white vision.

Cones:

• active in daylight;
• less numerous;
• provide daylight color vision.

In the adjacent layers of the retina there are neurons that perceive the nerve impulse from the receptors. The neurons of the retina form the optic nerve, which transmits impulses to the brain.

We look with two eyes, but we get one image because we use identical parts of the retina of both eyes. If you move the eyeball with your finger, the image immediately forks.

Table "Structure and functions of the eye"

Imaging

The eye is often compared to a camera, since in it an inverted and reduced image is obtained on the sensitive layer (retina). Children in the first months of life confuse the top and bottom of objects, but then their brain learns to “flip” the picture.

What have we learned?

We briefly reviewed the structure of the eye and the functions of its parts. The retina of the eye contains photoreceptors - the peripheral part of the visual analyzer. In receptor cells, the energy of light is converted into electrical energy of the nerve impulse. The optic nerve is formed from the processes of retinal neurons. The optical apparatus transmits and refracts light rays, projecting an image on the retina.

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