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

The structure of the human eye is almost identical to that of many animal species. Even sharks and squids have the same eye structure as a human. This suggests that this one appeared a very long time ago and has remained virtually unchanged over time. All eyes according to their structure can be divided into three types:

1. eyespot in unicellular and multicellular protozoa;
2. simple eyes of arthropods resembling a glass;

The structure 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. The slightest violation or a discrepancy in anatomy results in marked impairment of vision or complete blindness. Therefore, there are individual specialists who focus their efforts on this organ. It is extremely important for them to know in great 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 part of the 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. It is important muscular system eyes.

The eye itself consists of a light-refracting, accommodative and receptor system.

Image Acquisition Process

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

The final refraction of light occurs with the help of a lens. After which, having passed through vitreous, rays of light fall on the retina of the eye - a receptor screen that converts the information of the light flux into information of a 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 is, thanks to this part of the eye, a person’s field of vision is 190 degrees. Violations of this lens lead to tunnel vision.

The final refraction of light occurs in the lens of the eye, which focuses light rays onto a small area of ​​the retina. The lens is responsible for, changes in its shape lead to myopia or farsightedness.

Accommodative structure

This system regulates the intensity of 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.

Regulation of the light flux occurs due to changes in the diameter of the pupil, expansion or contraction of the iris. The circular muscles of the iris are responsible for the compression of the pupil, and the radial muscles of the iris are responsible for its expansion.

Receptor structure

Represented by a retina consisting of a photo receptor cells and the endings of neurons suitable for them. 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, divided according to their shape into rods and cones, are responsible for processing light information.

The structure of the human eye

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

A change in sagittal length leads to myopia 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 weight throughout our genus, it differs only by fractions of millimeters and milligrams.

Eyelids

Their purpose is to protect and moisturize the eye. Located on top of the eyelid thin layer skin and eyelashes, the latter are designed to remove dripping drops of sweat and protect the eye from dirt. The eyelid is equipped 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 moisturize the eyeball to reduce friction during its movement. The moisture itself is evenly distributed throughout the eye as a result of blinking.

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. This 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 junction of the upper and lower eyelids, half-closed upper eyelid does not promote uniform hydration. Blinking also protects the organ of vision from flying small particles of dust and insects. Blinking also helps eliminate foreign objects, the lacrimal glands are also responsible for this.

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; when they work uncoordinated, strabismus occurs. are divided into a dozen groups, the main ones being those that are responsible for the direction of a person’s gaze, the raising and lowering of the eyelid. Muscle tendons grow into the tissue of the sclerotic membrane.

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

Interesting fact: the Mayans considered squint beautiful, they special exercises developed 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 durable 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 movable diaphragm. It is involved in the regulation of the light flux passing through the pupil - the hole in it. To filter out light, the iris is opaque and has special muscles to dilate and constrict 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 extend 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 also 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. When the content is low, 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.

Interesting fact: the fingerprint pattern has 40 unique indicators, and the iris pattern has 256. This is why retinal scanning is used.

Interesting fact: blue eye color is a pathology; it appeared as a result of a mutation approximately 10,000 years ago. At the milestones blue-eyed people had 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 influence the curvature of the lens, thereby changing the focusing of the rays.

Retina

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

Interesting fact: children do not distinguish colors after birth; 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 own specific color: blue, green or red. There is a place on the retina where the optic nerve enters; there are no photoreceptor cells here. This area is called the "Blind Spot". There is also an area with the greatest content light-sensitive cells “Machine Spot”, it determines a clear picture in the center of the visual field. The retina is interesting in that it is loosely adjacent to the next vascular layer. Because of this, sometimes there is such a pathology as retinal detachment.

Our body interacts with the environment using sense organs, or analyzers. With their help, a person is not only able to “feel” the external world, based on 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 more than 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 perceiving the energy of external irritation and processing it into a nerve impulse;

Pathways through which the nerve impulse passes directly to the nerve center;

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

The rods consist of inner and outer segments. The latter is formed using double membrane disks, 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 the number of cones is only 5-7 million.

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

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

From each of the photoreceptor cells there is a thin process that forms a synapse (the place where two neurons contact) with another process of bipolar neurons (neuron II). The latter transmit excitation to larger ganglion cells (neuron III). The 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 neither nerves nor 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 distance vision, the lens flattens, and when set to near vision, it enlarges.

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, narrowing or expanding depending on the lighting. As a lens - the vitreous body and the lens. Light rays hit the retina, but the image comes out upside down.

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

Locomotor system

The motor apparatus of the eye consists of 4 striated rectus muscles (inferior, superior, lateral and medial) and 2 oblique muscles (inferior and superior). The rectus muscles are responsible for turning the eyeball in the appropriate 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, provide protection to 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.

A person blinks approximately once every 5-10 seconds.

Lacrimal apparatus

Consists of the lacrimal glands and lacrimal duct system. Tears neutralize microorganisms and can moisturize the conjunctiva. Without tears, the conjunctiva of the eye and the cornea would simply dry out, and the person would go blind.

The lacrimal glands produce about one hundred milliliters of tears every day. Interesting fact: women cry more often than men, because the secretion of tear fluid is promoted by the hormone prolactin (of which girls have much more).

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

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 schematically shows 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;

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 - blood vessels of the retina.

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

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 functions does the organ perform?

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

The organ of vision is a rather complex and not fully studied 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, forms of the surrounding world, the position of objects in space, etc.

Light can cause complex changes c and, thus, is an adequate irritant for the visual organs. It is believed that rhodopsin is 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 fovea. The further from the center the projection of the image of an object, the less distinct it is. This 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 title this disease- hypermetropia. A person with this disease has difficulty seeing objects that are close. Usually reading and working with small objects are difficult. It usually develops in older people, but can also appear in young people. Farsightedness can be completely cured only through surgical intervention.
2. Myopia (also called myopia). The disease is characterized by the inability to clearly see objects that are far enough away.
3. Glaucoma - increase intraocular pressure. Occurs due to impaired circulation of fluid in the eye. It is treated with medication, but in some cases surgery may be required.
4. 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, in 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 Treatments: Some can be cured with medication, while others can only be cured with surgery.

Disease Prevention

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

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

Do eye exercises more often and be examined by an ophthalmologist at least once a year.

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

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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 choroid (choroid) and consists of three parts - the iris, the ciliary (ciliary) body and the choroid itself.

Sagittal section of the eyeball

The retina (lat. retina) is the inner lining of the eyeball. The retina provides visual perception by converting light energy into the energy of a nerve impulse transmitted along a chain of neurons ( nerve cells) in the cerebral cortex. The retina is most firmly connected to the underlying membranes of the eyeball along the edge of the optic disc and in the area of ​​the dentate line. Retinal thickness different areas varies: at the edge of the optic disc it is 0.4-0.5 mm, in the central fovea 0.2–0.25 mm, in the fovea only 0.07–0.08 mm, in the area of ​​the dentate line about 0.1 mm.

The optic disc is the junction point 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 nerve head there is a physiological excavation (depression) where central artery and retinal vein.

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

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

The macula (synonyms: macular area, macula) has the shape of a horizontal oval with a diameter of about 5.5 mm. In the center of the macula there is a depression - 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 nerve head, 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. Thanks to the macula, we are able to read. Only the image focused in the macula can be perceived by the brain clearly and clearly.

Topography of the macular region

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

This is what 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) layer of rods and cones; 3) external glial limiting membrane; 4) outer granular layer; 5) outer mesh layer; 6) internal granular layer; 7) inner mesh layer; 8) ganglion layer; 9) layer of nerve fibers; 10) internal glial limiting membrane.

A peculiarity of the retina of the human eye is that it is of the inverted (inverted) type.

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, etc. Light, passing through the optical system of the eye, spreads as if 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, immediately adjacent to the underlying choroid, is the retinal pigment epithelium. It is a single layer of densely packed hexagonal cells containing large amounts of pigment. Pigment epithelial cells are multifunctional: they absorb excessive amounts of light falling on the photoreceptors (a few quanta of light are enough to generate a nerve impulse), participate in the process of destruction of dead rods and cones, in the processes of their recovery (regeneration), as well as in the metabolism of photoreceptors (cell activity ). Pigment epithelial cells are part of the so-called blood-retinal barrier, which ensures the selective flow 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 of the retina.

Rod-shaped (left) and cone-shaped (right) light sensitive cells(photoreceptors).

The total number of rods throughout the retina reaches 125–130 million, while cones are only about 6–7 million. The density of their arrangement in various areas the retina is not the same. Thus, within the central fovea, the density of cones reaches 110–150 thousand per 1 mm², rods are completely absent. As you move away from the fovea, the density of rods increases, and cones, on the contrary, decreases. At 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 lighting (day vision).

Cones provide color vision. There are “blue”, “green” and “red” cones, depending on the wavelength of light that is predominantly absorbed by their visual pigment (iodopsin). Rods are not capable of distinguishing colors; with their help we see in black and white. They contain the visual pigment rhodopsin.

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

The optic disc region is devoid of photoreceptors, and therefore physiologically represents a 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 (foveal area). The retinal vessels, which “cover” the photoreceptors at the places where they pass, are so-called angioscotomas (angio - vessel, scotoma - local area of ​​loss of the visual field); We do not see with these areas of the retina.

Blind spot test. Cover your left eye with your palm. With your right eye, look at the quadrangle on the left. Gradually move your face closer to the screen. At approximately a distance of 35-40 cm from the screen, the circle on the right will disappear. The explanation for this phenomenon is the following: under these conditions, the circle falls on the area of ​​the optic nerve head, which does not contain photoreceptors and therefore “disappears” from the field of vision. One has only to shift one's gaze slightly away from the quadrangle, and the circle appears again.

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

Retinal structure. The arrow shows the path of light rays. PE - pigment epithelium; K - cone; P - stick; B - bipolar cell; G - ganglion cell; A - amacrine cell, Go - horizontal cell (these two types of cells belong to the so-called interneurons, which provide connections between cells at the level of the layers of the retina), M - Müller 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 functions. 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 orbit.

The eye (the organ of vision) is located in the skull in the orbital cavity. It is held in place by several muscles located at the back and sides. They secure and provide motor activity, eye focusing.

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. Only the front, which consists of the cornea, is visually visible. 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 external (geometric, sagittal) axis.

If we connect the inner surface of the cornea to a point on the retina, we get the internal 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 membranes:

1. Protein is a fairly strong tissue that has connective characteristics. Its functions include protection against injury of various nature. The protein coat covers the entire visual analyzer. The front (visible) part is transparent - this is the cornea. The sclera is the posterior (invisible) protein membrane. 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 gives the eye its shape.
2. The middle ocular layer is tissue structure, which is permeated blood capillaries. Therefore, it is also called vascular. Its main function is to nourish the eye with all necessary substances and oxygen. It is thicker in the visible part and forms the ciliary muscle and body, which, by contracting, guarantees the ability 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 help the human eye regulate the amount of light that penetrates inside.
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 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.

Thanks to its optical abilities (changes in the shape of the lens), the organ of vision transmits images 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 physical activity.

Tear, which is produced by special glands, protects the eye from hypothermia, drying out and cleanses it of dust and debris.

All lacrimal apparatus consists of the following main parts:

• lacrimal gland;
• drainage ducts;
• lacrimal sac;
• tear duct;
• nasolacrimal duct.

Eyelids, eyelashes and eyebrows also have protective abilities. 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. The inside of the eyelid is covered with conjunctiva, and their edges are covered with cilia. The sebaceous glands are also located here, the secretion of which lubricates the edge of the eyelids.

General structure The organ of vision cannot be imagined without the muscular system, which ensures normal motor activity.

It consists of 6 muscle fibers:

• bottom;
• top;
• medial and lateral rectus;
• 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 course During pregnancy, a woman's eye structures are formed in a clear sequence. Already in a fully 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 (weight, shape, size, physiology).

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

• in the first six months, the baby’s macula and retina (fovea) develop;
• During the same period, the work developed visual pathways;
• formation of nervous reaction functions occurs up to 4 one month old;
• the final formation of cerebral cortex cells and their centers occurs within 24 months;
• During the first year of life, connections develop visual apparatus and other sense organs.

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

Starting from birth, a person must maintain visual hygiene, which will ensure long work analyzer. This is especially important when its development and formation occurs.

During this period, children's vision often deteriorates, which is associated with excessive load in the eyes, failure to comply with basic rules, for example, when reading, or insufficiency essential vitamins and microelements in the diet.

Let's look at some of the 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, ensure good lighting, which should be located 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 while lying down in public transport. Constant movement and changing the distance between the book and the eye apparatus leads to rapid fatigue, permanent shift focusing and malfunction muscles.
5. Provide your body completely enough vitamin A.

The eye is a complex optical apparatus of the human body. Its main function is to transmit images to the cerebral cortex for analysis of surrounding objects. At the same time, the brain and visual organs are closely connected. Therefore, it is very important to maintain 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, back in ancient times, described the retina of the eye: “A fishing net taken, thrown to the bottom of the eye glass, which catches Sun rays". This poetic comparison turned out to be surprisingly accurate. Today we can confidently say that the retina of the eye is precisely a “grid” capable of “catching” even individual quanta of light.

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

The retina of the eye occupies an area 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 zone where the optic nerve exits the fundus. With ophthalmoscopy, it looks like a light disk due to the higher light reflection coefficient (than in other areas of the retina).

Blind spot and central retinal area

In the area where the optic nerve exits, the retina does not have photosensitive receptors. Therefore, a person does not see the image of objects that fall into this place (hence the name “blind spot”). It measures approximately 1.8 - 2 mm in diameter, located in the 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 zone of the retina, called the macula, macula, or macular zone, appears as the darkest area of ​​the fundus. U 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 determined, but it is generally accepted that in the horizontal plane it ranges from 1.5 to 3 mm.

The macula, like the blind spot, is not located at the pole of the eyeball. Its center is shifted in the horizontal plane in the direction opposite to 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 different thicknesses. In the blind spot area it is 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 separating 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 falls on the photosensitive layer, composed of cones and rods. This layer actively absorbs light.

Cones have a length of 0.035 mm and a diameter from 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 for day “color” vision.

The most accepted is the three-component theory of G. Helmholtz, according to which the perception of color by the eye is ensured by three types of cones with different color sensitivities. Each cone has different concentrations three types of pigment - photosensitive substance:

— the first type of pigment (blue-blue) absorbs light in the wavelength range 435-450 nm;
- second type (green) - in the range of 525-540 nm;
- 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 quanta 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 luminous flux.

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

The density of cones and rods across the retina is not the same. The highest density is observed in the macula area. As you approach the periphery of the retina, the density decreases.

In the center of the fovea (foveola) there are only cones. Their diameter in this place is the smallest; they are tightly 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 greatest spatial resolution, and therefore is intended for observing the most important fragments of space on which a person fixes his gaze.

Further 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 highest in the parafoveoli - 150,000-160,000 per 1 mm. Further 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 (7,000,000 cones and 12,000,000 rods) and the 1.2 million fibers of the optic nerve. 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 is to carry out commutation 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 that the eye observes. Therefore, each cone from the foveal zone has its own personal channel for the passage of nerve impulses to the brain.

However, as we move away from the foveola, such channels are formed for groups of photoreceptors. This is served by the horizontal, bipolar amacrine and, as well as its external and internal layers. If each ganglion cell has only its own personal fiber (axon) for transmitting signals to the brain, this means that, thanks to the switching action of bipolar and horizontal cells, it must have synaptic contact with either one (in the foveal zone) or 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. top 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 “transfer of matter” along “conductor nerves”. 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 set of dendritic branches is called a dendritic tree.

Amacrine cells perform "lateral inhibition" between adjacent ganglion cells. This feedback switching of bipolar and ganglion cells is ensured. This not only solves the problem of connecting a limited number of nerve fibers to the brain large quantity photoreceptors, but also carries out preliminary 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, she is very fragile and important. Take care of her!