Structure and function of the retina. The structure of the main structures of the eye

The structure of the human eye is almost identical to its structure in many animal species. Even sharks and squids have human eye structure. This suggests that this one appeared a very long time ago and practically did not change over time. All eyes according to their device can be divided into three types:

1. eye spot in unicellular and protozoan multicellular organisms;
2. simple arthropod eyes resembling a glass;

The device of the eye is complex, it consists of more than a dozen elements. The structure of the human eye can be called the most complex and highly accurate in his body. slightest violation or a discrepancy in anatomy leads to a marked deterioration in vision or complete blindness. Therefore, there are individual specialists who focus their efforts on this body. It is extremely important for them to know in the smallest detail how the human eye works.

General information about the structure

The entire composition of the organs of vision can be divided into several parts. IN visual system includes not only the eye itself, but also the optic nerves coming from it, the area of ​​\u200b\u200bthe brain that processes incoming information, as well as organs that protect the eye from damage.

The protective organs of vision include the eyelids and lacrimal glands. Important is muscular system eyes.

The eye itself consists of a refractive, accommodative and receptor system.

Image Acquisition Process

Initially, the light passes through the cornea - a transparent section of the outer shell, which carries out the primary focusing of light. Some of the rays are filtered out by the iris, the other part passes through a hole in it - the pupil. Adaptation to the intensity of the light flux is carried out by the pupil by means of expansion or contraction.

The final refraction of light occurs with the help of a lens. Then after passing through vitreous body, rays of light fall on the retina of the eye - a receptor screen that converts the information of the light flux into information of the nerve impulse. The image itself is formed in the visual part of the human brain.

Apparatus for changing and processing light

Light refracting structure

It is a lens system. The first lens - thanks to this part of the eye, the field of view of a person is 190 degrees. Violations of this lens lead to tunnel vision.

The final refraction of light occurs in the lens of the eye, it focuses the rays of light on a small area of ​​the retina. The lens is responsible for changes in its shape leading to nearsightedness or farsightedness.

Accommodation structure

This system regulates the intensity of the incoming light and its focus. It consists of the iris, pupil, annular, radial and ciliary muscles, and the lens can also be attributed to this system. Focusing for seeing distant or close objects occurs by changing its curvature. The curvature of the lens is changed by the ciliary muscles.

The regulation of the light flux is due to a change in the diameter of the pupil, expansion or contraction of the iris. The annular muscles of the iris are responsible for the contraction of the pupil, and the radial muscles of the iris are responsible for its expansion.

Receptor structure

Represented by the retina, consisting of a photo receptor cells and suitable neuron endings. The anatomy of the retina is complex and heterogeneous, it has a blind spot and an area with hypersensitivity, it itself consists of 10 layers. Behind main function photoreceptor cells are responsible for processing light information, divided by shape into rods and cones.

human eye device

Only a small part is available for visual observation. eyeball, namely, one sixth. The rest of the eyeball is located in the depth of the orbit. Weight is approximately 7 grams. It is irregular in shape spherical shape, slightly elongated in the sagittal (deep) direction.

A change in sagittal length results in nearsightedness and farsightedness, as well as a change in the shape of the lens.

Interesting fact: the eye is the only part human body identical in size and mass in our entire genus, it differs only by fractions of millimeters and milligrams.

Eyelids

Their purpose is to protect and moisturize the eye. Above the eyelid is thin layer skin and eyelashes, the latter are designed to divert flowing drops of sweat and to protect the eye from dirt. The eyelid is supplied with an abundant network of blood vessels, it holds its shape with the help of a cartilaginous layer. Below is the conjunctiva slime layer containing many glands. The glands moisten the eyeball to reduce friction as it moves. The moisture itself is evenly distributed over the eye as a result of blinking.

An interesting fact: a person blinks 17 times per minute, when reading a book, the frequency is almost halved, and when reading text on a computer, it disappears almost completely. That is why the eyes get so tired from the computer.

For blinking, the main part of the eyelid is a muscular layer. Uniform hydration occurs at the connection of the upper and lower eyelids, semi-covered upper eyelid does not contribute to uniform hydration. Blinking also protects the organ of vision from flying small particles of dust and insects. Blinking also helps in excretion foreign objects, the lacrimal glands are also responsible for this.

An interesting fact: the muscles of the eyelid are the fastest, blinking takes 100-150 milliseconds, a person can blink at a speed of 5 times per second.

The direction of a person’s gaze depends on their work, with inconsistent work, strabismus occurs. are divided into a dozen groups, the main ones are those that are responsible for the direction of a person’s gaze, raising and lowering the eyelid. Muscle tendons grow into the tissue of the sclerotic membrane.

An interesting fact: the muscles of the eye are the most active, even the heart muscle is inferior to them.

Interesting fact: the Maya considered strabismus beautiful, they special exercises develop strabismus in their children.

Sclera and cornea

The sclera protects the structure human eye, it is represented fibrous tissue and covers 4/5 of its part. It is quite strong and dense. Thanks to these qualities, the structure of the eye does not change its shape, and the inner membranes are reliably protected. The sclera is opaque, White color("whites" of the eyes), contains blood vessels.

In contrast, the cornea is transparent, has no blood vessels, oxygen enters through upper layer from the surrounding air. The cornea is a very sensitive part of the eye, after damage it does not recover, resulting in blindness.

Iris and pupil

The iris is a moving diaphragm. It is involved in the regulation of the light flux passing through the pupil - a hole in it. To filter out light, the iris is opaque, has special muscles for expanding and narrowing the lumen of the pupil. The circular muscles surround the iris in a ring; when they contract, the pupil narrows. The radial muscles of the iris move away from the pupil like rays; when they contract, the pupil expands.

The iris has a variety of colors. The most common of them is brown, less common are green, gray and Blue eyes. But there are more exotic colors of the iris: red, yellow, purple and even white. Brown color acquired due to melanin, with a high content of it, the iris becomes black. With a low content, the iris acquires a gray, blue or blue tint. Red color is found in albinos, and yellow possible with lipofuscin pigment. Green color is a combination of blue and yellow.

An interesting fact: the fingerprint scheme has 40 unique indicators, and the iris scheme has 256. This is why the retinal scan is used.

An interesting fact: the blue color of the eyes is a pathology, it appeared as a result of a mutation about 10,000 years ago. At milestones blue-eyed people was a common ancestor.

lens

Its anatomy is quite simple. This is a biconvex lens, the main task of which is to focus the image on the retina. The lens is enclosed in a shell of single-layer cubic cells. It is fixed in the eye with the help of strong muscles, these muscles can affect the curvature of the lens, thereby changing the focus of the rays.

Retina

The multilayer receptor structure is located inside the eye, on its back wall. Her anatomy has been remapped to better handle incoming light. The basis of the receptor apparatus of the retina are cells: rods and cones. With a lack of light, clarity of perception is possible thanks to the sticks. Cones are responsible for color transmission. The conversion of the light flux into an electrical signal is carried out using photochemical processes.

An interesting fact: children do not distinguish colors after childbirth, the layer of cones is finally formed only after two weeks.

Cones respond to light waves in different ways. They are divided into three groups, each of which perceives only its specific color: blue, green or red. There is a place on the retina where the optic nerve enters, there are no photoreceptor cells. This area is called the "Blind Spot". There is also an area with the greatest content photosensitive cells "Yellow spot", it causes a clear picture in the center of the field of view. The retina is interesting in that it does not adhere tightly to the next vascular layer. Because of this, sometimes there is such a pathology as retinal detachment.

Our body interacts with the environment through the senses, or analyzers. With their help, a person is not only able to "feel" the outside world, on the basis of these sensations he has special forms reflections - self-awareness, creativity, the ability to foresee events, etc.

What is an analyzer?

According to I.P. Pavlov, each analyzer (and even the organ of vision) is nothing but a complex “mechanism”. He is able not only to receive signals environment and transform their energy into momentum, but also to produce the highest analysis and synthesis.

The organ of vision, like any other analyzer, consists of 3 integral parts:

The peripheral part, which is responsible for the perception of the energy of external irritation and its processing into a nerve impulse;

Conducting pathways, thanks to which the nerve impulse passes directly to the nerve center;

The cortical end of the analyzer (or sensory center), located directly in the brain.

Sticks consist of inner and outer segments. The latter is formed using double membrane discs, which are folds plasma membrane. Cones differ in size (they are larger) and the nature of the disks.

There are three types of cones and only one type of rods. The number of rods can reach 70 million, or even more, while cones - only 5-7 million.

As already mentioned, there are three types of cones. Each of them takes different colour: blue, red or yellow.

Sticks are needed to perceive information about the shape of the object and the illumination of the room.

From each of the photoreceptor cells, a thin process departs, which forms a synapse (the place where two neurons contact) with another process of bipolar neurons (neuron II). The latter transmit excitation to already larger ganglion cells (neuron III). Axons (processes) of these cells form the optic nerve.

lens

This is a biconvex crystal clear lens with a diameter of 7-10 mm. It has no nerves or blood vessels. Under the influence of the ciliary muscle, the lens is able to change its shape. It is these changes in the shape of the lens that are called accommodation of the eye. When set to far vision, the lens flattens out, and when set to near vision, it increases.

Together with the lens, it forms the refractive medium of the eye.

vitreous body

It fills all the free space between the retina and the lens. It has a jelly-like transparent structure.

The structure of the organ of vision is similar to the principle of the device of the camera. The pupil acts as a diaphragm, constricting or expanding depending on the light. As a lens - the vitreous body and the lens. Light rays hit the retina, but the image is upside down.

Thanks to the refractive media (thus the lens and the vitreous body), the light beam hits the macula on the retina, which is the best vision zone. Light waves reach cones and rods only after they have passed through the entire thickness of the retina.

locomotive apparatus

The motor apparatus of the eye consists of 4 striated rectus muscles (lower, upper, lateral and medial) and 2 oblique (lower and upper). The rectus muscles are responsible for turning the eyeball in the corresponding direction, and the oblique muscles are responsible for turning around the sagittal axis. The movements of both eyeballs are synchronous only thanks to the muscles.

Eyelids

Skin folds, the purpose of which is to limit the palpebral fissure and close it when closed, protect the eyeball from the front. There are about 75 eyelashes on each eyelid, the purpose of which is to protect the eyeball from foreign objects.

Approximately once every 5-10 seconds a person blinks.

lacrimal apparatus

Consists of the lacrimal glands and the lacrimal duct system. Tears neutralize microorganisms and are able to moisten the conjunctiva. Without tears, the conjunctiva of the eye and the cornea would simply dry up and the person would go blind.

The lacrimal glands produce about 100 milliliters of tears daily. An interesting fact: women cry more often than men, because the release of tear fluid is promoted by the hormone prolactin (which girls have much more).

Basically, a tear consists of water containing approximately 0.5% albumin, 1.5% sodium chloride, some mucus and lysozyme, which has bactericidal action. It has a slightly alkaline reaction.

The structure of the human eye: diagram

Let's take a closer look at the anatomy of the organ of vision with the help of drawings.

The figure above shows schematically parts of the organ of vision in a horizontal section. Here:

1 - tendon of the middle rectus muscle;

2 - rear camera;

3 - cornea eyes;

4 - pupil;

5 - lens;

6 - anterior chamber;

7 - iris of the eye;

8 - conjunctiva;

9 - tendon of the rectus lateral muscle;

10 - vitreous body;

11 - sclera;

12 - choroid;

13 - retina;

14 - yellow spot;

15 - optic nerve;

16 - retinal blood vessels.

This figure shows the schematic structure of the retina. The arrow shows the direction of the light beam. The numbers are marked:

1 - sclera;

2 - choroid;

3 - retinal pigment cells;

4 - sticks;

5 - cones;

6 - horizontal cells;

7 - bipolar cells;

8 - amacrine cells;

9 - ganglion cells;

10 - fibers optic nerve.

The figure shows a diagram of the optical axis of the eye:

1 - object;

2 - cornea of ​​​​the eye;

3 - pupil;

4 - iris;

5 - lens;

6 - central point;

7 - image.

What are the functions of the organ?

As already mentioned, human vision transmits almost 90% of the information about the world around us. Without him, the world would be the same type and uninteresting.

The organ of vision is a rather complex and not fully understood analyzer. Even in our time, scientists sometimes have questions about the structure and purpose of this organ.

The main functions of the organ of vision are the perception of light, the forms of the surrounding world, the position of objects in space, etc.

Light can cause complex changes in and, thus, is an adequate irritant for the organs of vision. Rhodopsin is believed to be the first to perceive irritation.

The highest quality visual perception will be provided that the image of the object falls on the area of ​​the retinal spot, preferably on its central fossa. The farther from the center the projection of the image of the object, the less distinct it is. Such is the physiology of the organ of vision.

Diseases of the organ of vision

Let's look at some of the most common eye diseases.

1. Farsightedness. Second name this disease- hypermetropia. A person with this disease does not see objects that are close. It is usually difficult to read, work with small objects. It usually develops in older people, but it can also appear in younger people. Farsightedness can be completely cured only with the help of surgical intervention.
2. Nearsightedness (also called myopia). The disease is characterized by the inability to see well objects that are far enough away.
3. Glaucoma - increase intraocular pressure. Occurs due to a violation of the circulation of fluid in the eye. It is treated with medication, but in some cases surgery may be required.
4. A cataract is nothing more than a violation of the transparency of the lens of the eye. Only an ophthalmologist can help get rid of this disease. Required surgical intervention at which a person's vision can be restored.
5. Inflammatory diseases. These include conjunctivitis, keratitis, blepharitis and others. Each of them is dangerous in its own way and has various methods treatment: some can be cured with medicines, and some only with the help of operations.

Disease prevention

First of all, you need to remember that your eyes also need to rest, and excessive loads will not lead to anything good.

Use only high-quality lighting with a lamp with a power of 60 to 100 watts.

Do exercises for the eyes more often and at least once a year undergo an examination by an ophthalmologist.

Remember that eye diseases are enough serious threat the quality of your life.

Website, Moscow
18.08.13 22:26

The eyeball has spherical shape. Its wall consists of three shells: outer, middle and inner. The outer (fibrous) membrane includes the cornea and sclera. The middle membrane is called the vascular (choroid) and consists of three parts - the iris, the ciliary (ciliary) body and the choroid itself.

Sagittal section of the eyeball

Retina (Latin retina) - the inner shell of the eyeball. The retina provides visual perception by converting light energy into the energy of a nerve impulse transmitted through a chain of neurons ( nerve cells) to the cerebral cortex. The retina is most strongly connected with the underlying membranes of the eyeball along the edge of the optic nerve head and in the region of the dentate line. The thickness of the retina different areas it is not the same: at the edge of the optic disc it is 0.4-0.5 mm, in the central fossa 0.2-0.25 mm, in the fovea only 0.07-0.08 mm, in the region of the dentate line about 0.1 mm.

The optic nerve head is the junction nerve fibers retina and represents the beginning of the optic nerve, which carries visual impulses to the brain. Its shape is round or somewhat oval, the diameter is approximately 1.5–2.0 mm. In the center of the optic disc there is a physiological excavation (deepening), where central artery and retinal vein.

The picture of the fundus is normal: 1) the optic disc (in the center of the disc is lighter - the excavation area); 2) yellow spot (macular area).

Section through the region of the optic nerve head: 1) arterial circle optic nerve (Zinn-Haller circle); 2) short ciliary (ciliary) artery; 3) sheaths of the optic nerve; 4) central artery and retinal vein; 5) ophthalmic artery and vein; 6) excavation of the optic disc.

The macula (synonyms: macular area, yellow spot) has the shape of a horizontal oval with a diameter of about 5.5 mm. There is a recess in the center of the macula fovea(fovea), and at the bottom of the latter there is a dimple (foveola). The foveola is located on the temporal side of the optic disc, at a distance of approximately 4 mm. The peculiarity of the foveola is that in this zone the density of photoreceptors is maximum and there are no blood vessels. This area is responsible for color perception and high visual acuity. The macula allows us to read. Only an image focused in the macula can be perceived clearly and distinctly by the brain.

Topography of the macular area

If you remember from the physics course, the image formed after the rays are refracted by a converging lens is an inverse (inverted), real image. The cornea and lens are two strong converging lenses, and therefore, after refraction of rays optical system eyes, in the macular region an inverted image of objects is formed.

This is how the image formed in the macular area looks like

The retina is a very complex organized structure. Microscopically, 10 layers are distinguished in it.

Microscopic structure of the retina: 1) pigment epithelium; 2) a layer of rods and cones; 3) outer glial limiting membrane; 4) outer granular layer; 5) outer mesh layer; 6) inner granular layer; 7) inner mesh layer; 8) ganglionic layer; 9) a layer of nerve fibers; 10) internal glial limiting membrane.

A feature of the retina of the human eye is that it belongs to the type of inverted (inverted).

The layers of the retina are counted from outside to inside, i.e. the pigment epithelium, which is directly adjacent to the choroid, is the first layer, the layer of photoreceptors (rods and cones) is the second layer, and so on. Light passing through the optical system of the eye propagates, as it were, from the inside of the eyeball outward, and in order to reach the layer of photoreceptors that are turned away from light, it must pass through the entire thickness of the retina.

The first layer of the retina, directly bordering the underlying choroid, is the retinal pigment epithelium. This is one layer of densely packed hexagonal cells containing a large amount of pigment. The cells of the pigment epithelium are multifunctional: they absorb an excessive amount of light that enters the photoreceptors (a few photons of light are enough for a nerve impulse to occur), participate in the process of destruction of dead rods and cones, in the processes of their restoration (regeneration), as well as in the metabolism of photoreceptors (the life of the cell). ). Pigment epithelium cells are part of the so-called hematoretinal barrier, which ensures the selective entry of certain substances from the blood capillaries of the choroid into the retina.

The second layer of the retina is represented by light-sensitive cells (photoreceptors). These cells got their name (cone-like and rod-like or simply cones and rods) because of the shape of the outer segment. Rods and cones are the first neuron in the retina.

Rod-like (left) and cone-like (right) photosensitive cells(photoreceptors).

The total number of rods throughout the retina reaches 125–130 million, while there are only about 6–7 million cones. The density of their arrangement in different areas the retina is not the same. So, within the central fossa, the density of cones reaches 110-150 thousand per 1 mm², rods are completely absent. With distance from the fovea, the density of the rods increases, and cones, on the contrary, decreases. On the periphery of the retina, rods are mainly present.

Rods and cones have different light sensitivity: the former function in low light and are responsible for twilight vision, the latter, on the contrary, can function only in sufficiently bright light (day vision).

Cones provide color vision. Allocate "blue", "green" and "red" cones, depending on the wavelength of light, which is predominantly absorbed by their visual pigment (iodopsin). The rods are not able to distinguish colors, with their help we see in black and white. They contain the visual pigment rhodopsin.

Visual pigments are located in special membrane disks of cones and rods, which are located in their outer segments. Stick disks are constantly updated (every 40 minutes a new disk is created) when active participation pigment epithelium. The disks of cones are not renewed during the life of the cell, only some of their important components are replaced.

The region of the optic nerve head is devoid of photoreceptors, therefore physiologically it is the so-called "blind spot". We do not see in this area of ​​the field of view.

Schematic representation of the visual fields: the cross in the center is the point of gaze fixation (the fovea area). The vessels of the retina, which “cover” the photoreceptors in the places of their passage, are the so-called angioscotomas (angio - vessel, scotoma - local area of ​​visual field loss); we do not see these parts of the retina.

Blind spot test. Close your left eye with your palm. With your right eye, look at the quadrangle on the left. Gradually bring your face closer to the screen. At a distance of about 35-40 cm from the screen, the circle on the right will disappear. The explanation for this phenomenon is as follows: under these conditions, the circle falls on the area of ​​the optic disc, which does not contain photoreceptors and therefore "disappears" from the field of view. One has only to slightly shift the gaze away from the quadrangle, and the circle reappears.

The layers of the retina are a series of three neurons and their intercellular connections.

The structure of the retina. The arrow shows the path of light rays. PE - pigment epithelium; K - cone; P - wand; B - bipolar cell; G - ganglion cell; A - amacrine cell, Go - horizontal cell (these two types of cells belong to the so-called intercalary neurons, which provide connections between cells at the level of the layers of the retina), M - Muller cell (a cell that provides a supporting, supporting function, its processes form the outer and inner glial boundary membrane of the retina).

One of the main organs, which is directly related to the perception of the world around us, is the eye analyzer. The organ of vision plays a primary role in the diverse human activities, in its evolution it has reached perfection and performs important features. With the help of the eye, a person selects colors, captures streams of light rays and directs them to light-sensitive cells, recognizes three-dimensional images and distinguishes objects at various distances from him. The human organ of vision is paired and is located in the cranial eye socket.

The eye (organ of vision) is located in the cranium in the orbital cavity. It is held by several muscles located behind and on the sides. They secure and provide motor activity, eye focus.

The anatomy of the organ of vision distinguishes three main parts:

• eyeball;
• nerve fibers;
• auxiliary parts (muscles, eyelashes, glands that produce tears, eyebrows, eyelids).

The shape of the eyeball is spherical. Visually visible only in front, which consists of the cornea. Everything else lies deep in the eye socket. The average size of the eyeball in an adult is 2.4 cm. It is calculated by measuring the distance between the anterior and posterior poles. The straight line that connects this gap is the outer (geometric, sagittal) axis.

If we connect the inner surface of the cornea with a point on the retina, we get the inner axis of the body of the eye, which is located at the posterior pole. Its average length is 2.13 cm.

The main part of the eyeball is a transparent substance, which is enveloped in three shells:

1. Protein is a fairly strong tissue that has the characteristics of a connective tissue. Its function is to protect against injury. different nature. The protein shell covers the entire visual analyzer. The front (visible) part is transparent - this is the cornea. The sclera is the posterior (invisible) protein coat. It is a continuation of the cornea, but differs from it in that it is not a transparent structure. The density of the protein shell provides the eye with its shape.
2. The middle ocular membrane is tissue structure which is pierced blood capillaries. Therefore, it is also called vascular. Its main function is to nourish the eye with all essential substances and oxygen. It is thicker in the visible part and forms the ciliary muscle and body, which, by contracting, guarantees the possibility of the lens to bend. The iris is a continuation ciliary body. It consists of several layers. It is here that there are cells responsible for pigmentation, they determine the shade of the eyes. The pupil looks like a hole that is located in the center of the iris. It is surrounded by circular muscle fibers. Their function is to contract the pupil. Another group of muscles (radical), on the contrary, dilates the pupil. All together helps the human eye regulate the amount of light that enters.
3. The retina is the inner shell, consists of the back and the visual part. The anterior retina has pigment cells and neurons.

In addition, the organ of vision has a lens, aqueous humor and the vitreous body. They are an internal component of the eye and part of the optical system. They break and conduct rays of light through internal structure eyes and focus the image on the retina.

Due to its optical abilities (changes in the shape of the lens), the organ of vision transmits an image of objects that are located at different distances from visual analyzer.

Anatomy of the auxiliary parts of the visual analyzer

The anatomy and physiology of the organ of vision also consists of an auxiliary apparatus. He performs protective function and provides movement.

A tear, which is produced by special glands, protects the eye from hypothermia, drying out and cleans dust and debris.

Whole lacrimal apparatus consists of the following main parts:

• lacrimal gland;
• outlet ducts;
• lacrimal sac;
• lacrimal canal;
• nasolacrimal duct.

Protective abilities also have eyelids, eyelashes and eyebrows. The latter protect the visual apparatus from above and have a hairy structure. They wick away sweat. The eyelids are folds of skin that, when closed, completely hide the eyeball. They protect visual organ from harsh light, dust. From the inside, the eyelid is covered with conjunctiva, and their edges are covered with cilia. The sebaceous glands are also located here, the secret of which lubricates the edge of the eyelids.

General structure the organ of vision cannot be imagined without a muscular apparatus that provides normal motor activity.

It consists of 6 muscle fibers:

• bottom;
• top;
• medial and lateral straight line;
• oblique.

The work of the entire visual analyzer depends on their ability to contract and relax.

Stages of development of the human eye and the secrets of good vision

Anatomy and physiology of the organ of vision has different characteristics at all stages of its formation. At normal flow Pregnancy in a woman, all the structures of the eye are formed in a clear sequence. Already in the formed 9-month-old fetus, the organ of vision has all fully developed membranes. But there are some differences between the eye of an adult and a newborn (mass, shape, size, physiology).

The development of the eye after birth goes through certain stages:

• in the first six months, the child develops a yellow spot and retina (central fovea);
• during the same period, the development of work visual pathways;
• the formation of the functions of nervous reactions occurs up to 4 one month old;
• the final formation of the cells of the cerebral cortex and their centers occurs within 24 months;
• during the first year of life, the development of ties is observed visual apparatus and other sense organs.

So, gradually the organ of vision is formed and improved. Its development continues until puberty. During this period, the eyes of a child almost completely correspond to the parameters of an adult.

Starting from birth, a person must observe the hygiene of the organs of vision, which will ensure long work analyzer. This is especially important when its development and formation takes place.

During this period, children's vision often deteriorates, which is associated with excessive load on the eyes, not following the basic rules, for example, when reading, or insufficiency essential vitamins and micronutrients in the diet.

Let's look at some of important rules visual hygiene, which must be observed not only during the period when development occurs, but throughout life:

1. Protect your eyes from mechanical and chemical negative impact.
2. When reading, provide good lighting, which should be on the left side. But at the same time, it should not be too bright, as this renders light-sensitive cells unusable. Provide soft lighting.
3. The distance from the book to the eyes should not be less than 35 cm.
4. Do not read in transport, lying down. Constant movement and changing the distance between the book and the eye apparatus leads to rapid fatigue, permanent shift focus and wrong work muscles.
5. Completely supply the body enough vitamin A.

The eye is a complex optical apparatus of the human body. Its main function is to transmit an image to the cerebral cortex for analysis of surrounding objects. At the same time, the brain and organs of vision are closely related. Therefore, it is very important to preserve the basic functions of our visual analyzer.

People at all times thought about the complex structure human body. This is how the wise Greek Herophilus described the retina of the eye in ancient times: Sun rays". This poetic comparison turned out to be surprisingly accurate. Today it can be confidently asserted that the retina of the eye is precisely a "grid" capable of "catching" even individual light quanta.

The retina can be defined as a multi-element photodetector of images, which, according to a simplified structure, is represented as a branching of the optic nerve with additional features image processing.

The retina of the eye occupies a zone with a diameter of about 22 mm, and due to this, almost completely (about 72% inner surface eyeball) covers the fundus of the eye with photoreceptors from the ciliary body to the blind spot - the exit zone from the fundus of the optic nerve. With ophthalmoscopy, it looks like a light disk due to the higher (than in other areas of the retina) light reflectance.

Blind spot and central retinal area

In the exit zone of the optic nerve, the retina does not have photosensitive receptors. Therefore, the image of objects that fall into this place, a person does not see (hence the name "blind spot"). It has a size of approximately 1.8 - 2 mm in diameter, located in a horizontal plane at a distance of 4 mm from the posterior pole of the eyeball towards the nose below the pole of the eyeball.

The central area of ​​the retina, which is called the macula, macula or macular area, looks like the darkest area of ​​the fundus. At different people its color can vary from dark yellow to dark brown. The central zone has a somewhat elongated oval shape in the horizontal plane. The size of the macula is not precisely defined, but it is generally accepted that in the horizontal plane it is from 1.5 to 3 mm.

The yellow spot, like the blind spot, is not located in the zone of the pole of the eyeball. Its center is displaced in the horizontal plane in the opposite direction from the blind spot: at a distance of about 1 mm from the axis of symmetry of the optical system of the eye.

The retina of the eye has a different thickness. In the blind spot area, it is the thickest (0.4 - 0.5 mm). It has the smallest thickness in the central zone of the macula (0.07 - 0.1 mm), where the so-called central fossa is formed. At the edges of the retina (the dentate line), its thickness is approximately 0.14 mm.

Although the retina looks like a thin film, it still has a complex microstructure. In the direction of the rays that enter the retina through the transparent media of the eye and the membrane that separates the vitreous body from the retina, the first layer of the retina is transparent nerve fibers. They are "conductors" through which photoelectric signals are transmitted to the brain, carrying information about the visual picture of objects of observation: images that are focused by the optical system of the eye on the fundus.

Light, the distribution density of which on the surface of the retina is proportional to the brightness of the field of objects, penetrates through all layers of the retina and enters the light-sensitive layer, composed of cones and rods. This layer performs active absorption of light.

The cones have a length of 0.035 mm and a diameter of 2 µm in the central zone of the macula to 6 µm in the peripheral zone of the retina. The sensitivity threshold of cones is approximately 30 quanta of light, and the threshold energy is 1.2 10 -17 J. Cones are photoreceptors of the "color" vision day.

The three-component theory of G. Helmholtz, according to which the perception of color by the eye is provided by three types of cones with different color sensitivity, enjoys the greatest acceptability. Each cone has different concentration three types of pigment - a photosensitive substance:

- the first type of pigment (blue-blue) absorbs light in the wavelength range of 435-450 nm;
- the second type (green) - in the range of 525-540 nm;
- the third type (red) - in the range of 565-570 nm.

Rods are receptors for night, "black and white" vision. Their length is 0.06 mm, and their diameter is about 2 microns. They have a threshold sensitivity of 12 photons of light at a wavelength of 419 nm or a threshold energy of 4.8 0 -18 J. Therefore, they are much more sensitive to light flux.

However, due to the weak spectral sensitivity of the rods, objects of observation at night are perceived by a person as gray or black and white.

The density of cones and rods on the retina is not the same. The greatest density is observed in the area of ​​the yellow spot. When approaching the periphery of the retina, the density decreases.

In the center of the fovea (foveoli) are only cones. Their diameter in this place is the smallest, they are densely hexagonally enclosed. In the foveal zone, the density of cones is 147,000-238,000 per 1 mm. This area of ​​the retina has the highest spatial resolution, and therefore is intended to observe the most important fragments of space on which a person fixes his gaze.

Farther from the center, the density decreases to 95,000 per 1 mm, and in the parafovea, to 10,000 per 1 mm. The density of rods is the highest in the parafoveoli - 150,000-160,000 per 1 mm. Farther from the center, their density also decreases, and at the periphery of the retina it is only 60,000 per 1 mm. The average density of rods on the retina is 80,000-100,000 per 1 mm.

Retinal Functions

There is a discrepancy between the number of individual photoreceptors (7000000 cones and 120000000 rods) and 1.2 million optic nerve fibers. It manifests itself in the fact that the number of "photodetectors" is more than 10 times greater than the number of "conductors" that connect the retina with the corresponding centers of the brain.

This makes clear the function of the layers of the retina: it consists in switching between individual photoreceptors and areas of the visual center of the brain. On the one hand, they do not overload the brain with “small”, secondary information, and on the other hand, they do not allow the loss of an important component of visual information about the environment observed by the eye. Therefore, each cone from the foveal zone has its own personal channel for the passage of nerve impulses to the brain.

However, as one moves away from the foveola, such channels are already formed for groups of photoreceptors. This is served by horizontal, bipolar amacrine and, as well as its outer and inner layers. If each ganglion cell has only its own personal fiber (axon) to transmit signals to the brain, this means that, due to the switching action of bipolar and horizontal cells, it must have synaptic contact either with one (in the foveola zone) or with several (in the peripheral zone) photoreceptors.

It is clear that for this it is necessary to carry out the corresponding horizontal switching of photoreceptors and bipolar cells at a lower level, as well as bipolar and ganglion cells at a lower level. highest level. Such switching is provided through the processes of horizontal and amacrine cells.

Synaptic contacts are electrochemical contacts (synapses) between cells, which are carried out due to electrochemical processes involving specific substances (neurotransmitters). They ensure the "transfer of matter" through the "nerves-conductors". Therefore, connections between different dendrites of the retina depend not only on nerve impulses, but also on processes throughout the body. These processes can deliver neurotransmitters to the synaptic zones in the retina and to the brain both with the participation of nerve impulses and with the flow of blood and other fluids.

Dendrites are processes of nerve cells that receive signals from other neurons, receptor cells, and conduct nerve impulses through synaptic contacts to the body of neurons. The collection of dendrites forms a dendritic branch. The collection of dendritic branches is called a dendritic tree.

Amacrine cells perform "lateral inhibition" between adjacent ganglion cells. This feedback switching of bipolar and ganglionic cells is provided. This not only solves the problem of connecting a limited number of nerve fibers to the brain a large number photoreceptors, but also pre-processing of information coming from the retina to the brain, that is, spatial and temporal filtering of visual signals.

These are the functions of the retina. As you can see, it is very fragile and important. Take care of her!