Systems and parts of the eye structure functions. The structure of the human eye photo with a description

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 chiasm. 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 eyeball consists of three shells: outer, middle and inner. The outer, or fibrous, membrane is formed from dense connective tissue - the cornea (in front) and an opaque sclera, or tunica (back). The middle (vascular) membrane contains blood vessels and consists of three sections:

1) anterior section (iris, or iris). The iris contains smooth muscle fibers that make up two muscles: a circular, constricting pupil, located almost in the center of the iris, and a radial, dilating the pupil. Closer to the anterior surface of the iris is a pigment that determines the color of the eye and the opacity of this shell. The iris adjoins with its back surface to the lens;

2) middle section (ciliary body). The ciliary body is located at the junction of the sclera with the cornea and has up to 70 ciliary radial processes. Inside the ciliary body is the ciliary, or ciliary, muscle, which consists of smooth muscle fibers. The ciliary muscle is attached by ciliary ligaments to the tendon ring and the lens bag;

3) the posterior section (the choroid itself).

The most complex structure has an inner shell (retina). The main receptors in the retina are rods and cones. The human retina contains about 130 million rods and about 7 million cones. Each rod and cone has two segments - outer and inner, the cone has a shorter outer segment. The outer segments of the rods contain visual purple, or rhodopsin (purple substance), in the outer segments of the cones - iodopsin (violet). The inner segments of the rods and cones are connected to neurons that have two processes (bipolar cells) that are in contact with ganglion neurons that are part of the optic nerve with their fibers. Each optic nerve contains about 1 million nerve fibers.

The distribution of rods and cones in the retina has the following order: in the middle of the retina there is a central fovea (yellow spot) with a diameter of 1 mm, it contains only cones, closer to the central fossa are cones and rods, and on the periphery of the retina - only rods. In the fovea, each cone is connected to one neuron through a bipolar cell, and to the side of it, several cones are also connected to one neuron. Rods, unlike cones, are connected to one bipolar cell in several pieces (about 200). Due to this structure, the greatest visual acuity is provided in the fovea. At a distance of approximately 4 mm medially from the central fossa is the papilla of the optic nerve (blind spot), in the center of the nipple are the central artery and the central vein of the retina.

Between the posterior surface of the cornea and the anterior surface of the iris and part of the lens is the anterior chamber of the eye. Between the posterior surface of the iris, the anterior surface of the ciliary ligament and the anterior surface of the lens is the posterior chamber of the eye. Both chambers are filled with transparent aqueous humor. The entire space between the lens and the retina is occupied by a transparent vitreous body.

Light refraction in the eye. The refractive media of the eye include: the cornea, the aqueous humor of the anterior chamber of the eye, the lens and the vitreous body. In many ways, the clarity of vision depends on the transparency of these media, but the refractive power of the eye depends almost entirely on the refraction in the cornea and lens. Refraction is measured in diopters. The diopter is the reciprocal of the focal length. The refractive power of the cornea is constant and equal to 43 diopters. The refractive power of the lens is unstable and varies over a wide range: when looking at the near distance - 33 diopters, at a distance - 19 diopters. The refractive power of the entire optical system of the eye: when looking into the distance - 58 diopters, at a short distance - 70 diopters.

Parallel light rays, after refraction in the cornea and lens, converge to one point in the fovea. The line passing through the centers of the cornea and lens to the center of the macula is called the visual axis.

Accommodation. The ability of the eye to clearly distinguish objects at different distances is called accommodation. The phenomenon of accommodation is based on the reflex contraction or relaxation of the ciliary, or ciliary, muscle, innervated by the parasympathetic fibers of the oculomotor nerve. Contraction and relaxation of the ciliary muscle changes the curvature of the lens:

a) when the muscle contracts, the ciliary ligament relaxes, which causes an increase in light refraction, because the lens becomes more convex. Such a contraction of the ciliary muscle, or visual tension, occurs when an object approaches the eye, that is, when viewing an object that is as close as possible;

b) when the muscle relaxes, the ciliary ligaments stretch, the lens bag squeezes it, the curvature of the lens decreases and its refraction decreases. This occurs when the object is removed from the eye, i.e., when looking into the distance.

The contraction of the ciliary muscle begins when an object approaches a distance of about 65 m, then its contractions increase and become distinct when an object approaches a distance of 10 m. Further, as the object approaches, the contractions of the muscles increase more and more and finally reach the limit at which clear vision becomes impossible. The minimum distance from an object to the eye at which it is clearly visible is called the nearest point of clear vision. In a normal eye, the far point of clear vision is at infinity.

Farsightedness and myopia. A healthy eye, when looking into the distance, refracts a beam of parallel rays so that they are focused in the fovea. With myopia, parallel rays are focused in front of the fovea, diverging rays fall into it and therefore the image of the object is blurred. The causes of myopia may be the tension of the ciliary muscle during accommodation at a close distance or too long the longitudinal axis of the eye.

In farsightedness (due to a short longitudinal axis), parallel rays are focused behind the retina, and converging rays enter the fovea, which also causes blurred images.

Both vision defects can be corrected. Myopia is corrected by biconcave lenses, which reduce refraction and shift the focus to the retina; farsightedness - biconvex lenses that increase the refraction and therefore move the focus to the retina.

Located in the eye socket (orbit). The walls of the orbit are formed by the facial and cranial bones. The visual apparatus consists of the eyeball, optic nerve and a number of auxiliary organs (muscles, lacrimal apparatus, eyelids). Muscles allow the eyeball to move. These are a pair of oblique muscles (upper and lower muscles) and four rectus muscles (upper, lower, internal and external).

The eye as an organ

The human organ of vision is a complex structure that includes:

• Peripheral organ of vision (eyeball with appendages);
• Pathways (optic nerve, optic tract);
• Subcortical centers and higher visual centers.

The peripheral organ of vision (eye) is a paired organ, the device of which allows you to perceive light radiation.

Eyelashes and eyelids perform a protective function. Accessory organs include the lacrimal glands. Tear fluid is needed to warm, moisturize and clean the surface of the eyes.

Basic structures

The eyeball is an organ of complex structure. The internal environment of the eye is surrounded by three shells: outer (fibrous), middle (vascular) and inner (reticulate). The outer shell for the most part consists of protein opaque tissue (sclera). In its anterior part, the sclera passes into the cornea: the transparent part of the outer shell of the eye. Light enters the eyeball through the cornea. The cornea is also necessary for the refraction of light rays.

The cornea and sclera are strong enough. This allows them to maintain intraocular pressure and maintain the shape of the eye.

The middle layer of the eye is:

• Iris;
• Vascular membrane;
• Ciliary (ciliary) body.

The iris consists of loose connective tissue and a network of blood vessels. In its center is the pupil - a hole with a diaphragm device. In this way, it can regulate the amount of light entering the eye. The edge of the iris passes into the ciliary body, covered with sclera. The annular ciliary body consists of the ciliary muscle, vessels, connective tissue and processes of the ciliary body. The lens is attached to the processes. The functions of the ciliary body are the process of accommodation and production. This fluid nourishes some parts of the eye and maintains a constant intraocular pressure.

It also forms the substances necessary to ensure the process of vision. In the next layer of the retina are processes called rods and cones. Through the processes, the nervous excitation that provides visual perception is transmitted to the optic nerve. The active part of the retina is called the fundus, which contains blood vessels, and the macula, where most of the cone processes responsible for color vision are located.

Shape of rods and cones

Inside the eyeball are:

• intraocular fluid;
• vitreous body.

The posterior surface of the eyelids and the anterior part of the eyeball over the sclera (to the cornea) are covered by the conjunctiva. This is the mucous membrane of the eye, which looks like a thin transparent film.

The structure of the anterior part of the eyeball and lacrimal apparatus

Optical system

Depending on the functions performed by different parts of the organs of vision, it is possible to distinguish between the light-transmitting and light-perceiving parts of the eye. The light-perceiving part is the retina. The image of objects perceived by the eye is reproduced on the retina using the optical system of the eye (the light-conducting section), which consists of the transparent medium of the eye: the vitreous body, the moisture of the anterior chamber and the lens. But mainly the refraction of light occurs on the outer surface of the eye: the cornea and in the lens.

Optical system of the eye

Rays of light pass through these refractive surfaces. Each of them deflects a light beam. In the focus of the optical system of the eye, the image appears as its inverted copy.

The process of refraction of light in the optical system of the eye is denoted by the term "refraction". The optical axis of the eye is a straight line that passes through the center of all refractive surfaces. Light rays emanating from infinitely distant objects are parallel to this straight line. Refraction in the optical system of the eye collects them in the main focus of the system. That is, the main focus is the place where objects at infinity are projected. From objects that are at a finite distance, the rays, refracting, are collected in additional foci. Additional tricks are further than the main one.

In studies of the functioning of the eye, the following parameters are usually taken into account:

• Refractive, or refraction;
• Corneal curvature radius;
• Refractive index of the vitreous.

It is also the radius of curvature of the retinal surface.

Age development of the eye and its optical power

After the birth of a person, his organs of vision continue to form. In the first six months of life, the area of ​​the macula and the central area of ​​the retina are formed. The functional mobility of the visual pathways also increases. During the first four months, the morphological and functional development of the cranial nerves occurs. Until the age of two years, the improvement of the cortical visual centers, as well as the visual cellular elements of the cortex, continues. In the first years of a child's life, the connections between the visual analyzer and other analyzers are formed and strengthened. The development of human organs of vision is completed by the age of three.

Light sensitivity in a child appears immediately after birth, but a visual image cannot yet appear. Quite quickly (within three weeks), the baby develops conditioned reflex connections, which lead to the improvement of the functions of spatial, objective and.

Central vision develops in humans only in the third month of life. Subsequently, it is improved.

The visual acuity of the newborn is very low. By the second year of life, it rises to 0.2–0.3. By the age of seven, it develops to 0.8–1.0.

The ability to perceive color appears at the age of two to six months. At the age of five, color vision in children is fully developed, although it continues to improve. Also gradually (approximately by school age) they reach the normal level of the border of the field of view. Binocular vision develops much later than other functions of the eye.

Adaptation

Adaptation is the process of adapting the organs of vision to a changing level of illumination of the surrounding space and objects in it. Distinguish between the process of dark adaptation (changes in sensitivity when moving from bright light to complete darkness) and light adaptation (when moving from darkness to light).

The "adaptation" of the eye, which perceived bright light, to vision in the dark develops unevenly. At first, the sensitivity increases quite quickly, and then slows down. Complete completion of the dark adaptation process can take several hours.

Light adaptation takes a much shorter period of time - about one to three minutes.

Accommodation

Accommodation is the process of "adaptation" of the eye to a clear distinction between those objects that are located in space at different distances from the perceiver. The mechanism of accommodation is associated with the possibility of changing the curvature of the surfaces of the lens, that is, changing the focal length of the eye. This occurs when the ciliary body is stretched or relaxed.

With age, the ability of the organs of vision to accommodate gradually decreases. Develops (age farsightedness).

Visual acuity

The concept of "visual acuity" refers to the ability to see separately points that are located in space at a certain distance from each other. In order to measure visual acuity, the concept of "visual angle" is used. The smaller the angle of view, the higher the visual acuity. Visual acuity is considered one of the most important functions of the eye.

Determining visual acuity is one of the key work of the eye.

Hygiene is a part of medicine that develops rules that are important for preventing diseases and promoting the health of various organs and body systems. The main rule aimed at maintaining the health of vision is to prevent eye fatigue. It is important to learn how to relieve stress, use vision correction methods if necessary.

Also, hygiene of vision provides for measures that protect the eyes from pollution, injuries, burns.

Hygiene

Workplace equipment is part of the activities that allow the eyes to function normally. The organs of vision "work" best in conditions closest to natural. Unnatural lighting, low eye mobility, dry indoor air can lead to visual impairment.

Eye health is greatly influenced by the quality of nutrition.

Exercises

There are quite a few exercises that help maintain good vision. The choice depends on the state of vision of a person, his capabilities, lifestyle. It is best to get expert advice when choosing certain types of gymnastics.

A simple set of exercises designed to relax and train:

1. Blink intensively for one minute;
2. "Blink" with closed eyes;
3. Direct your gaze to a certain point located far from the person. Look into the distance for a minute;
4. Look at the tip of the nose, look at it for ten seconds. Then again look into the distance, close your eyes;
5. Lightly patting with your fingertips, massage the eyebrows, temples and infraorbital region. After that, you need to cover your eyes with your palm for one minute.

Exercise should be done once or twice a day. It is also important to use the complex to relax from intense visual stress.

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conclusions

The eye is a sensory organ that provides the function of vision. Most of the information about the world around us (about 90%) comes to a person through vision. The unique optical system of the eye allows you to get a clear image, distinguish colors, distances in space, and adapt to changing lighting conditions.

The eyes are a complex and sensitive organ. Its pretty, but also creating unnatural operating conditions. In order to maintain eye health, hygiene recommendations must be followed. In the event of problems with vision or the occurrence of eye diseases, it is necessary to seek the advice of a specialist. This will help a person maintain visual functions.

Undoubtedly, each of the sense organs 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 - one 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;
  • accessory system;
  • propulsion system.
• Area responsible for conducting nerve signals.
• subcortical centers.
• Cortical visual centers.

Anatomy of the structure of the human eye

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

Outer layer of the eye represented by connective tissue. The anterior zone is called the cornea, it has a transparent structure. The back zone is the sclera, better known as the protein. Due 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. Corneal cells form a clear order, it is he who provides the ability 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 zone of the fibrous layer is very significant. This is due to the fact that the zone is a place of concentration of nerve endings.

Sclera (protein). Differs in opacity and durability. The composition includes fibers having 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, is the pupil. Muscles inside the iris allow the pupil to change in diameter. This happens when they contract and relax. It is important to note that the indicated zone determines the shade of human eyes.

Ciliary or ciliary body. Location - the 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 the eye fluid. Special ligaments attached to the vessels, in turn, fix the lens.

Choroid. Posterior zone of the middle shell. Represented by arteries and veins, with their help, other parts of the eye are nourished.

Inner lining of the eye- retina. The thinnest of all three shells. Represented by different types of cells: rods and cones.

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

The 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 is in the macula or corpus luteum. The main function of this zone is to provide visual acuity.

The ocular nucleus (eye cavity). The kernel 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 with the pupil. Due to this, intraocular fluid easily circulates between the two cavities.

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

• capsule;
• capsular epithelium;
• crystalline substance.

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

vitreous body. Occupies most of the eye. The consistency is like a gel. Main components: water and hyaluronic acid. Provides nutrition to the retina and enters the optical system of the eye. The vitreous body consists of three components:

• directly vitreous body;
• boundary membrane;
• klyuev channel.

In this video you will see how the human eye works.

Protective system of the eye

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 the skin. The main task is to protect the eye. 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 on the entire surface of the eyelids from the inside.

Conjunctiva. The 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 sheets of the conjunctiva, a hollow space is formed, which protects 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 the outer surface of the eye, 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 are responsible for eye movement. Muscles originate in the eye socket. Following the entire eye, the muscles end in the protein.

In addition, in this system there are muscles due to which the eyelids can close and open - the muscle that lifts the eyelid, and the circular or orbital muscle.

Photo of the structure of the human eye

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

The organ of vision is the most important of all human senses, because about 90% of information about the outside world a person receives through a visual analyzer or visual system.

The organ of vision is the most important of all human senses, because about 90% of information about the outside world a person receives through a visual analyzer or visual system. The main functions of the organ of vision are central, peripheral, color and binocular vision, as well as light perception.

A person sees not with his eyes, but through his eyes, from where information is transmitted through the optic nerve to certain areas of the occipital lobes of the cerebral cortex, where the picture of the outside world that we see is formed.

The structure of the visual system

The visual system consists of:

* Eyeball;

* Protective and auxiliary apparatus of the eyeball (eyelids, conjunctiva, lacrimal apparatus, oculomotor muscles and orbital fascia);

* Life support systems of the organ of vision (blood supply, production of intraocular fluid, regulation of hydro and hemodynamics);

* Conducting pathways - optic nerve, optic chiasm and optic tract;

* Occipital lobes of the cerebral cortex.

Eyeball

The eye has the shape of a sphere, so the allegory of an apple began to be applied to it. The eyeball is a very delicate structure, therefore it is located in the bony recess of the skull - the eye socket, where it is partially sheltered from possible damage.

The human eye is not quite the correct spherical shape. In newborns, its dimensions are (on average) along the sagittal axis 1.7 cm, in adults 2.5 cm. The mass of the eyeball of a newborn is up to 3 g, an adult - up to 7-8 g.

Features of the structure of the eyes in children

In newborns, the eyeball is relatively large, but short. By 7-8 years, the final size of the eyes is established. The newborn has a relatively larger and flatter cornea than adults. At birth, the shape of the lens is spherical; throughout life, it grows and becomes flatter. In newborns, there is little or no pigment in the stroma of the iris. The bluish color of the eyes is due to the translucent posterior pigment epithelium. When the pigment begins to appear in the iris, it takes on its own color.

The structure of the eyeball

The eye is located in the orbit and is surrounded by soft tissues (fatty tissue, muscles, nerves, etc.). In front, it is covered with conjunctiva and covered with eyelids.

Eyeball consists of three membranes (outer, middle and inner) and contents (vitreous body, lens, and aqueous humor of the anterior and posterior chambers of the eye).

Outer, or fibrous, shell of the eye represented by dense connective tissue. It consists of a transparent cornea in the anterior part of the eye and a white opaque sclera. With elastic properties, these two shells form the characteristic shape of the eye.

The function of the fibrous membrane is to conduct and refract light rays, as well as protect the contents of the eyeball from adverse external influences.

Cornea- transparent part (1/5) of the fibrous membrane. The transparency of the cornea is due to the uniqueness of its structure, in it all the cells are located in a strict optical order and there are no blood vessels in it.

The cornea is rich in nerve endings, so it is very sensitive. The impact of unfavorable external factors on the cornea causes a reflex contraction of the eyelids, providing protection for the eyeball. The cornea not only transmits, but also refracts light rays, it has a large refractive power.

Sclera- the opaque part of the fibrous membrane, which has a white color. Its thickness reaches 1 mm, and the thinnest part of the sclera is located at the exit of the optic nerve. The sclera consists mainly of dense fibers that give it strength. Six oculomotor muscles are attached to the sclera.

Functions of the sclera- protective and shaping. Numerous nerves and vessels pass through the sclera.

choroid, the middle layer, contains the blood vessels that carry blood to feed the eye. Just below the cornea, the choroid passes into the iris, which determines the color of the eyes. At its center is pupil. The function of this shell is to limit the entry of light into the eye at high brightness. This is achieved by constricting the pupil in high light and dilating in low light.

Behind the iris is located lens, similar to a biconvex lens that catches light as it passes through the pupil and focuses it on the retina. Around the lens, the choroid forms a ciliary body, in which the ciliary (ciliary) muscle is embedded, which regulates the curvature of the lens, which provides a clear and distinct vision of objects at different distances.

When this muscle is relaxed, the ciliary band attached to the ciliary body is stretched and the lens is flattened. Its curvature, and hence the refractive power, is minimal. In this state, the eye sees distant objects well.

In order to see near objects, the ciliary muscle contracts and the tension of the ciliary girdle weakens, so that the lens becomes more convex, hence more refractive.

This property of the lens to change its refractive power of the beam is called accommodation.

Inner shell eyes presented retina– highly differentiated nervous tissue. The retina of the eye is the front edge of the brain, an extremely complex formation both in structure and in function.

Interestingly, during embryonic development, the retina is formed from the same group of cells as the brain and spinal cord, so it is true to say that the retinal surface is an extension of the brain.

In the retina, light is converted into nerve impulses, which are transmitted along the nerve fibers to the brain. There they are analyzed, and the person perceives the image.

The main layer of the retina is a thin layer of light-sensitive cells - photoreceptors. They are of two types: responding to weak light (rods) and strong (cones).

Sticks there are about 130 million, and they are located throughout the retina, except for the very center. Thanks to them, a person sees objects on the periphery of the field of view, including in low light.

There are about 7 million cones. They are located mainly in the central zone of the retina, in the so-called yellow spot. The retina here is maximally thinned, all layers are missing, except for the layer of cones. A person sees best with a yellow spot: all light information that falls on this area of ​​\u200b\u200bthe retina is transmitted most fully and without distortion. Only day and color vision is possible in this area.

Under the influence of light rays in photoreceptors, a photochemical reaction occurs (disintegration of visual pigments), as a result of which energy (electric potential) is released that carries visual information. This energy in the form of nervous excitation is transmitted to other layers of the retina - to bipolar cells, and then to ganglion cells. At the same time, due to the complex connections of these cells, random “noise” in the image is removed, weak contrasts are enhanced, moving objects are perceived more sharply.

Ultimately, all visual information in an encoded form is transmitted in the form of impulses along the fibers of the optic nerve to the brain, its highest instance - the posterior cortex, where the visual image is formed.

Interestingly, the rays of light, passing through the lens, are refracted and turned over, due to which an inverted reduced image of the object appears on the retina. Also, the picture from the retina of each eye enters the brain not entirely, but as if cut in half. However, we see the world normally.

Therefore, it is not so much in the eyes as in the brain. In essence, the eye is simply a perceiving and transmitting instrument. The brain cells, having received an inverted image, turn it over again, creating a true picture of the surrounding world.

Contents of the eyeball

The contents of the eyeball are the vitreous body, the lens, and the aqueous humor of the anterior and posterior chambers of the eye.

The vitreous body by weight and volume is approximately 2/3 of the eyeball and more than 99% consists of water, in which a small amount of protein, hyaluronic acid and electrolytes are dissolved. This is a transparent, avascular gelatinous formation that fills the space inside the eye.

The vitreous body is quite firmly connected with the ciliary body, the lens capsule, as well as with the retina near the dentate line and in the region of the optic nerve head. With age, the connection with the lens capsule weakens.

Auxiliary apparatus of the eye

The auxiliary apparatus of the eye includes the oculomotor muscles, lacrimal organs, as well as the eyelids and conjunctiva.

oculomotor muscles

The oculomotor muscles provide the mobility of the eyeball. There are six of them: four straight and two oblique.

The rectus muscles (superior, inferior, external, and internal) originate from a ring of tendons located at the apex of the orbit around the optic nerve and insert into the sclera.

The superior oblique muscle starts from the periosteum of the orbit above and medially from the visual opening, and, going somewhat backwards and downwards, is attached to the sclera.

The inferior oblique muscle originates from the medial wall of the orbit behind the inferior orbital fissure and inserts on the sclera.

The blood supply to the oculomotor muscles is carried out by the muscular branches of the ophthalmic artery.

The presence of two eyes allows us to make our vision stereoscopic (that is, to form a three-dimensional image).

Precise and well-coordinated work of the eye muscles allows us to see the world around us with two eyes, i.e. binocularly. In case of dysfunction of the muscles (for example, with paresis or paralysis of one of them), double vision occurs or the visual function of one of the eyes is suppressed.

It is also believed that the oculomotor muscles are involved in the process of adjusting the eye to the process of vision (accommodation). They compress or stretch the eyeball so that the rays coming from the observed objects, whether far or near, can hit the retina exactly. In this case, the lens provides finer adjustment.

Blood supply to the eye

The brain tissue that conducts nerve impulses from the retina to the visual cortex, as well as the visual cortex, normally almost everywhere has a good supply of arterial blood. Several large arteries that are part of the carotid and vertebrobasilar vascular systems participate in the blood supply of these brain structures.

Arterial blood supply to the brain and visual analyzer is carried out from three main sources - the right and left internal and external carotid arteries and the unpaired basilar artery. The latter is formed as a result of the fusion of the right and left vertebral arteries located in the transverse processes of the cervical vertebrae.

Almost the entire visual cortex and partly the cortex of the parietal and temporal lobes adjacent to it, as well as the occipital, midbrain and pontine oculomotor centers are supplied with blood by the vertebrobasilar basin (vertebra - translated from Latin - vertebra).

In this regard, circulatory disorders in the vertebrobasilar system can cause dysfunction of both the visual and oculomotor systems.

Vertebrobasilar insufficiency, or vertebral artery syndrome, is a condition in which blood flow in the vertebral and basilar arteries is reduced. The cause of these disorders may be compression, increased tone of the vertebral artery, incl. as a result of compression by bone tissue (osteophytes, herniated disc, subluxation of the cervical vertebrae, etc.).

As you can see, our eyes are an exceptionally complex and amazing gift of nature. When all departments of the visual analyzer work harmoniously and without interference, we see the world around us clearly.

Treat your eyes carefully and carefully!