home Audience 12 How does the human eye work and how does it work? How does the human eye work and how does it work?

How does the human eye work and how does it work? How does the human eye work and how does it work?

The eye apparatus is stereoscopic and in the body is responsible for the correct perception of information, the accuracy of its processing and further transmission to the brain.

The right part of the retina, through transmission through the optic nerve, sends information from the right lobe of the image to the brain, left side transmits left lobe, as a result, the brain connects both, and a common visual picture is obtained.

The lens is fixed with thin threads, one end of which is tightly woven into the lens, its capsule, and the other end is connected to the ciliary body.

When the tension of the threads changes, the process of accommodation occurs . The lens is deprived lymphatic vessels and blood vessels, as well as nerves.

It provides the eye with light conduction and refraction, gives it the function of accommodation, and is the separator of the eye into posterior section and anterior section.

Vitreous body

The vitreous body of the eye is the largest formation. This is a colorless gel-like substance, which is formed in the form of a spherical shape, it is flattened in the sagittal direction.

The vitreous body consists of a gel-like substance of organic origin, a membrane and a vitreous canal.

In front of it is the lens, zonular ligament and ciliary processes, its posterior part comes close to the retina. Compound vitreous and retina occurs at optic nerve and in the part of the dentate line, where the flat part of the ciliary body is located. This area is the base of the vitreous body, and the width of this belt is 2-2.5 mm.

Chemical composition of the vitreous body: 98.8 hydrophilic gel, 1.12% dry residue. When hemorrhage occurs, the thromboplastic activity of the vitreous increases sharply.

This feature is aimed at stopping bleeding. IN in good condition The vitreous body has no fibrinolytic activity.

Nutrition and maintenance of the vitreous environment is provided by diffusion nutrients, which through the glassy membrane enter the body from intraocular fluid and osmosis.

There are no vessels or nerves in the vitreous body, and its biomicroscopic structure is various forms tapes gray with white specks. Between the ribbons there are areas without color, completely transparent.

Vacuoles and opacities in the vitreous appear with age. In cases where partial loss of the vitreous body occurs, the area is filled with intraocular fluid.

Aqueous humor chambers

The eye has two chambers that are filled with aqueous humor. Moisture is formed from the blood by processes of the ciliary body. Its release occurs first into the anterior chamber, then it enters the anterior chamber.

Aqueous humor enters the anterior chamber through the pupil. The human eye produces from 3 to 9 ml of moisture per day. The aqueous humor contains substances that nourish the lens, the endothelium of the cornea, the anterior part of the vitreous, and the trabecular meshwork.

It contains immunoglobulins, which help remove hazardous factors from the eye, its inner part. If outflow aqueous humor is disturbed, it can develop an eye disease such as glaucoma, as well as increase the pressure inside the eye.

In cases of violation of the integrity of the eyeball, loss of aqueous humor leads to hypotony of the eye.

Iris

The iris is the avant-garde part of the vascular tract. It is located immediately behind the cornea, between the cameras and in front of the lens. The iris has round shape and is located around the pupil.

It consists of the boundary layer, the stromal layer and the pigment-muscle layer. It has an uneven surface with a pattern. The iris contains pigment cells, which are responsible for eye color.

The main tasks of the iris are: regulation of the light flux that passes to the retina through the pupil and protection of light-sensitive cells. Visual acuity depends on the correct functioning of the iris.

The iris has two groups of muscles. One group of muscles is located around the pupil and regulates its reduction, the other group is located radially along the thickness of the iris, regulating the dilation of the pupil. The iris has many blood vessels.

Retina

Is optimal thin shell nerve tissue and represents you the peripheral department visual analyzer. The retina contains photoreceptor cells that are responsible for perception, as well as for converting electromagnetic radiation into nerve impulses. It is adjacent to the vitreous body on the inside, and to the vascular layer of the eyeball on the outside.

The retina has two parts. One part is the visual part, the other is the blind part, which does not contain photosensitive cells. The internal structure of the retina is divided into 10 layers.

The main task of the retina is to receive the light flux, process it, converting it into a signal, which forms complete and encoded information about the visual image.

Optic nerve

The optic nerve is a network of nerve fibers. Among these thin fibers is the central canal of the retina. The starting point of the optic nerve is in the ganglion cells, then its formation occurs by passing through the sclera and the growth of nerve fibers with meningeal structures.

The optic nerve has three layers - hard, arachnoid, soft. There is liquid between the layers. Diameter optic disc is about 2 mm.

Topographic structure of the optic nerve:

intraocular;
intraorbital;
intracranial;
intratubular;

How the human eye works

The light flux passes through the pupil and through the lens is brought into focus on the retina. The retina is rich in light-sensitive rods and cones, of which there are more than 100 million in the human eye.

Video: "The Process of Vision"

Rods provide sensitivity to light, and cones give the eye the ability to distinguish colors and small details. After refraction of the light flux, the retina transforms the image into nerve impulses. These impulses then go to the brain, which processes the incoming information.

Diseases

Diseases associated with disturbances in the structure of the eyes can be caused either by the incorrect location of its parts in relation to each other, or by internal defects of these parts.

The first group includes diseases that lead to a decrease in visual acuity:

Myopia. It is characterized by an increased length of the eyeball compared to the norm. This causes the light passing through the lens to focus not on the retina, but in front of it. The ability to see objects located at a distance from the eyes is impaired. Myopia corresponds to a negative number of diopters when measuring visual acuity.
Farsightedness. It is a consequence of a decrease in the length of the eyeball or loss of elasticity by the lens. In both cases, accommodation capabilities are reduced, correct focusing of the image is disrupted, and light rays converge behind the retina. The ability to see objects located nearby is impaired. Farsightedness corresponds to a positive number of diopters.
Astigmatism. This disease is characterized by a violation of the sphericity of the eye shell due to defects in the lens or cornea. This leads to uneven convergence of light rays entering the eye, and the clarity of the image received by the brain is disrupted. Astigmatism is often accompanied by nearsightedness or farsightedness.

Pathologies associated with functional disorders certain parts of the organ of vision:

Cataract. With this disease, the lens of the eye becomes cloudy, its transparency and ability to transmit light are impaired. Depending on the degree of clouding, visual impairment can vary, up to and including complete blindness. For most people, cataracts occur in old age but do not progress to severe stages.
Glaucoma – pathological change intraocular pressure. It can be provoked by many factors, for example, a decrease in the anterior chamber of the eye or the development of cataracts.
Myodesopsia or “flying spots” before the eyes. It is characterized by the appearance of black dots in the field of vision, which can be presented in different quantities and sizes. The spots arise due to disturbances in the structure of the vitreous body. But the causes of this disease are not always physiological - “floaters” can appear due to overwork or after suffering from infectious diseases.
Strabismus. Triggered by change correct position eyeball in relation to the eye muscle or malfunction eye muscles.
Retinal detachment. Retina and back vascular wall are separated from each other. This occurs due to a violation of the tightness of the retina, which occurs when its tissue ruptures. Detachment is manifested by clouding of the outlines of objects before the eyes, and the appearance of flashes in the form of sparks. If individual corners disappear from the field of view, this means that the detachment has become severe forms. If left untreated, complete blindness occurs.
Anophthalmos is insufficient development of the eyeball. Rare congenital pathology, the reason for which is a violation of the formation frontal lobes brain Anophthalmos can also be acquired, then it develops after surgical operations(for example, to remove tumors) or severe eye injuries.

Prevention

You should take care of your health circulatory system, especially the part that is responsible for blood flow to the head. Many visual defects occur due to atrophy and damage to the optic and brain nerves.
Avoid eye strain. When working with constant viewing of small objects, you need to take regular breaks and perform eye exercises. Workplace should be arranged so that the brightness of lighting and the distance between objects are optimal.
Getting enough minerals and vitamins into the body is another condition for maintaining healthy vision. Vitamins C, E, A and minerals such as zinc are especially important for the eyes.
Proper eye hygiene helps prevent the development of inflammatory processes, complications of which can significantly impair vision.

Associate Professor of the Department of Eye Diseases. | Chief Editor site

Practices emergency, outpatient and routine ophthalmology. Conducts diagnostics and conservative treatment farsightedness, allergic diseases eyelids, myopia. Performs probing, removal foreign bodies, fundus examination with a three-mirror lens, rinsing the nasolacrimal ducts.

In the morning, as soon as we open our eyes, they begin to collect information and send it to the brain for decoding. The eyes are an extremely sensitive and complex device. They must be protected from bright light sunlight And accidental damage, for example, when you go out for a walk. In this article you will learn how the eye works.

The work of the eye resembles the work of a camera. Light enters the eye through the pupil. Light passes through the lens (behind the pupil) and is refracted at the retina. It converts the image into nerve impulses, which are then transmitted to the brain, where all information about light and shape is processed. The retina contains millions of special light-sensitive cells called rods and cones. Rods are sensitive to light, and thanks to cones we distinguish colors and small details.

Reliable protection

Eyebrows, eyelashes and eyelids protect the eyes from dust. For example, on a hot day, droplets of sweat stop the eyebrows, and on a rainy day, droplets of rain stop them. Eyelashes trap dust particles that can get into your eyes. And our eyelids are a kind of curtains made of folds of skin that rise and fall with the help of muscles. These curtains move so quickly that they do not interfere with our eyes at all. We don't even notice it.

Do not Cry!

Do you like to cry? Of course not - any of you will answer. Meanwhile, every time you blink, you cry. The fact is that there is a special gland in the eye that stores liquid - tears. When you blink, the eyelid opens the lacrimal gland, thereby flushing the eye. And if some irritant gets there (for example, smoke or onions), then the number of tears increases greatly.

Why are the eyes different colors?

The color of the eye depends on the content of the dye in the iris. It is called melanin and is inherited by a person from his parents. Brown eye color is the most common in the world. Most rare color- blue.

Why can't people see in the dark?

When there is not enough light, the cones (cells that recognize color) cannot work effectively. At this time, the sticks (reacting to light) continue to work until it gets completely dark. But with their help we see the world in shades of black and white, and the image clarity decreases.

- Every day the eye makes more than 60 thousand movements when we look around, up or down.

- There are approximately 1% of people on earth whose left and right eyes are different colors.

- When exposed to daylight or too much cold, a person's eye color may change.

Vision is the channel through which a person receives approximately 70% of all data about the world that surrounds him. And this is possible only for the reason that human vision is one of the most complex and amazing visual systems on our planet. If there were no vision, we would all most likely simply live in the dark.

The human eye has a perfect structure and provides vision not only in color, but also in three dimensions and with the highest sharpness. It has the ability to instantly change focus to a variety of distances, regulate the volume of incoming light, distinguish between a huge number of colors, and more. large quantity shades, correct spherical and chromatic aberrations, etc. The eye brain is connected to six levels of the retina, in which the data goes through a compression stage even before information is sent to the brain.

But how does our vision work? How do we transform color reflected from objects into an image by enhancing color? If you think about this seriously, you can conclude that the structure of the human visual system is “thought out” to the smallest detail by the Nature that created it. If you prefer to believe that the Creator or some other person is responsible for the creation of man High power, then you can attribute this merit to them. But let's not understand, but continue talking about the structure of vision.

Huge amount of details

The structure of the eye and its physiology can frankly be called truly ideal. Think for yourself: both eyes are located in the bony sockets of the skull, which protect them from all kinds of damage, but they protrude from them in such a way as to ensure the widest possible horizontal vision.

The distance the eyes are from each other provides spatial depth. And the eyeballs themselves, as is known for certain, have a spherical shape, due to which they are able to rotate in four directions: left, right, up and down. But each of us takes all this for granted - few people imagine what would happen if our eyes were square or triangular or their movement was chaotic - this would make vision limited, chaotic and ineffective.

So, the structure of the eye is extremely complex, but this is precisely what makes the work of about four dozen of its different components possible. And even if at least one of these elements were missing, the process of vision would cease to be carried out as it should be carried out.

To see how complex the eye is, we invite you to pay attention to the figure below.

Let's talk about how the process of visual perception is implemented in practice, what elements of the visual system are involved in this, and what each of them is responsible for.

Passage of light

As light approaches the eye, light rays collide with the cornea (otherwise known as the cornea). The transparency of the cornea allows light to pass through it inner surface eyes. Transparency, by the way, is the most important characteristic cornea, and it remains transparent due to the fact that a special protein it contains inhibits the development of blood vessels - a process that occurs in almost every tissue human body. If the cornea were not transparent, the remaining components of the visual system would have no significance.

Among other things, the cornea prevents debris, dust and any other substances from entering the internal cavities of the eye. chemical elements. And the curvature of the cornea allows it to refract light and help the lens focus light rays on the retina.

After light has passed through the cornea, it passes through a small hole located in the middle of the iris. The iris is a round diaphragm that is located in front of the lens just behind the cornea. The iris is also the element that gives the eye color, and the color depends on the predominant pigment in the iris. The central hole in the iris is the pupil familiar to each of us. The size of this hole can be changed to control the amount of light entering the eye.

The size of the pupil will be changed directly by the iris, and this is due to its unique structure, because it consists of two various types muscle tissue (even there are muscles here!). The first muscle is a circular compressor - it is located in the iris in a circular manner. When the light is bright, it contracts, as a result of which the pupil contracts, as if being pulled inward by a muscle. The second muscle is an extension muscle - it is located radially, i.e. along the radius of the iris, which can be compared to the spokes of a wheel. In dark lighting, this second muscle contracts, and the iris opens the pupil.

Many still experience some difficulties when they try to explain how the formation of the above-mentioned elements of the human visual system occurs, because in any other intermediate form, i.e. at any evolutionary stage they simply would not be able to work, but man sees from the very beginning of his existence. Mystery…

Focusing

Bypassing the above stages, light begins to pass through the lens located behind the iris. The lens is an optical element shaped like a convex oblong ball. The lens is absolutely smooth and transparent, there are no blood vessels in it, and it itself is located in an elastic sac.

Passing through the lens, light is refracted, after which it is focused on the fovea of the retina - the most sensitive place containing the maximum number of photoreceptors.

It is important to note that the unique structure and composition provide the cornea and lens with a high refractive power, guaranteeing a short focal length. And how amazing it is that such a complex system fits in just one eyeball (just think what a person could look like if, for example, a meter was required to focus light rays coming from objects!).

No less interesting is that the combined refractive power of these two elements (cornea and lens) is in excellent correlation with the eyeball, and this can be safely called another proof that visual system created simply unsurpassed, because the process of focusing is too complex to talk about it as something that happened only through step-by-step mutations - evolutionary stages.

If we are talking about objects located close to the eye (as a rule, a distance of less than 6 meters is considered close), then everything is even more curious, because in this situation the refraction of light rays turns out to be even stronger. This is ensured by an increase in the curvature of the lens. The lens is connected through ciliary bands to the ciliary muscle, which, when contracted, allows the lens to take on a more convex shape, thereby increasing its refractive power.

And here again we cannot fail to mention the most complex structure lens: it consists of many threads, which consist of cells connected to each other, and thin belts connect it with the ciliary body. Focusing is carried out under the control of the brain extremely quickly and completely “automatically” - it is impossible for a person to carry out such a process consciously.

Meaning of "camera film"

The result of focusing is the concentration of the image on the retina, which is multilayer fabric, sensitive to light, covering the back of the eyeball. The retina contains approximately 137,000,000 photoreceptors (for comparison, we can cite modern digital cameras, which have no more than 10,000,000 such sensory elements). Such a huge number of photoreceptors is due to the fact that they are located extremely densely - approximately 400,000 per 1 mm².

It would not be out of place here to cite the words of microbiologist Alan L. Gillen, who speaks in his book “The Body by Design” about the retina of the eye as a masterpiece of engineering design. He believes that the retina is the most amazing element of the eye, comparable to photographic film. The light-sensitive retina, located on the back of the eyeball, is much thinner than cellophane (its thickness is no more than 0.2 mm) and much more sensitive than any human-made photographic film. The cells of this unique layer are capable of processing up to 10 billion photons, while the most sensitive camera can process only a few thousand. But what’s even more surprising is that human eye can capture single photons even in the dark.

In total, the retina consists of 10 layers of photoreceptor cells, 6 layers of which are layers of light-sensitive cells. There are 2 types of photoreceptors special form, which is why they are called cones and rods. Rods are extremely sensitive to light and provide the eye with black-and-white perception and night vision. Cones, in turn, are not so sensitive to light, but are able to distinguish colors - optimal performance of cones is noted in daytime days.

Thanks to the work of photoreceptors, light rays are transformed into complexes of electrical impulses and sent to the brain at incredible speeds. high speed, and these impulses themselves travel over a million nerve fibers in a fraction of a second.

The communication of photoreceptor cells in the retina is very complex. Cones and rods are not directly connected to the brain. Having received the signal, they redirect it to bipolar cells, and they redirect the signals they have already processed to ganglion cells, more than a million axons (neurites along which nerve impulses are transmitted) which form a single optic nerve, through which data enters the brain.

Two layers of interneurons, before visual data is sent to the brain, facilitate parallel processing of this information by six layers of perception located in the retina. This is necessary so that images are recognized as quickly as possible.

Brain perception

After the processed visual information enters the brain, it begins to sort, process and analyze it, and also forms a complete image from individual data. Of course, about work human brain There is still a lot that is unknown, but even what the scientific world can provide today is quite enough to be amazed.

With the help of two eyes, two “pictures” of the world that surrounds a person are formed - one for each retina. Both “pictures” are transmitted to the brain, and in reality the person sees two images at the same time. But how?

But the point is this: the retinal point of one eye exactly corresponds to the retinal point of the other, and this suggests that both images, entering the brain, can overlap each other and be combined together to obtain a single image. The information received by the photoreceptors in each eye converges in the visual cortex, where a single image appears.

Due to the fact that the two eyes may have different projections, some inconsistencies may be observed, but the brain compares and connects the images in such a way that a person does not perceive any inconsistencies. Moreover, these inconsistencies can be used to obtain a sense of spatial depth.

As is known, due to the refraction of light visual images, entering the brain, are initially very small and upside down, but “at the output” we get the image that we are used to seeing.

In addition, in the retina, the image is divided by the brain in two vertically - through a line that passes through the retinal fossa. The left parts of the images received by both eyes are redirected to , and the right parts are redirected to the left. Thus, each of the hemispheres of the viewing person receives data from only one part of what he sees. And again - “at the output” we get a solid image without any traces of connection.

The separation of images and extremely complex optical pathways make it so that the brain sees separately from each of its hemispheres using each of the eyes. This allows you to speed up the processing of the flow of incoming information, and also provides vision with one eye if suddenly a person for some reason stops seeing with the other.

We can conclude that the brain, in the process of processing visual information, removes “blind” spots, distortions due to micro-movements of the eyes, blinks, angle of view, etc., offering its owner an adequate holistic image of what is being observed.

Another one of important elements the visual system is . There is no way to downplay the importance of this issue, because... In order to be able to use our vision properly at all, we must be able to turn our eyes, raise them, lower them, in short, move our eyes.

In total there are 6 external muscles, which connect to the outer surface of the eyeball. These muscles include 4 rectus muscles (inferior, superior, lateral and middle) and 2 obliques (inferior and superior).

At the moment when any of the muscles contracts, the muscle that is opposite to it relaxes - this ensures smooth eye movement (otherwise all eye movements would be jerky).

When you turn both eyes, the movement of all 12 muscles (6 muscles in each eye) automatically changes. And it is noteworthy that this process is continuous and very well coordinated.

According to the famous ophthalmologist Peter Janey, control and coordination of the communication of organs and tissues with the central nervous system through the nerves (this is called innervation) of all 12 eye muscles is one of the very complex processes, occurring in the brain. If we add to this the accuracy of gaze redirection, the smoothness and evenness of movements, the speed with which the eye can rotate (and it amounts to a total of up to 700° per second), and combine all this, we will actually get a phenomenal movement in terms of performance. ocular system. And the fact that a person has two eyes makes it even more complex - with synchronous eye movements, the same muscular innervation is necessary.

The muscles that rotate the eyes are different from the skeletal muscles because... they are made up of many different fibers, and they are also controlled a large number neurons, otherwise precision of movements would become impossible. These muscles can also be called unique because they are able to contract quickly and practically do not get tired.

Considering that the eye is one of the most important organs human body, he needs continuous care. It is precisely for this purpose that an “integrated cleaning system” is provided, so to speak, which consists of eyebrows, eyelids, eyelashes and lacrimal glands.

With the help of the lacrimal glands, a sticky liquid is regularly produced, moving at a slow speed down the outer surface eyeball. This liquid washes away various debris (dust, etc.) from the cornea, after which it enters the internal lacrimal canal and then flows down the nasal canal, being eliminated from the body.

Tears contain a very strong antibacterial substance that destroys viruses and bacteria. The eyelids act as windshield wipers - they clean and moisturize the eyes through involuntary blinking at intervals of 10-15 seconds. Along with the eyelids, eyelashes also work, preventing any debris, dirt, germs, etc. from entering the eye.

If the eyelids did not fulfill their function, a person's eyes would gradually dry out and become covered with scars. If it weren't for tear duct, the eyes would constantly be filled with tear fluid. If a person did not blink, debris would get into his eyes and he could even go blind. The entire “cleaning system” must include the work of all elements without exception, otherwise it would simply cease to function.

Eyes as an indicator of condition

A person’s eyes are capable of transmitting a lot of information during his interaction with other people and the world around him. The eyes can radiate love, burn with anger, reflect joy, fear or anxiety, or fatigue. The eyes show where a person is looking, whether he is interested in something or not.

For example, when people roll their eyes while talking to someone, this can be interpreted very differently from a normal upward gaze. Big eyes children cause delight and tenderness among those around them. And the state of the pupils reflects the state of consciousness in which this moment time there is a person. Eyes are an indicator of life and death, if we speak in a global sense. This is probably why they are called the “mirror” of the soul.

Instead of a conclusion

In this lesson we looked at the structure of the human visual system. Naturally, we missed a lot of details (this topic itself is very voluminous and it is problematic to fit it into the framework of one lesson), but we still tried to convey the material so that you have a clear idea of HOW a person sees.

You couldn't help but notice that both the complexity and capabilities of the eye allow this organ to surpass even the most modern technologies and scientific developments. The eye is clear demonstration the complexity of engineering in a huge number of nuances.

But knowing about the structure of vision is, of course, good and useful, but the most important thing is to know how vision can be restored. The fact is that a person’s lifestyle, the conditions in which he lives, and some other factors (stress, genetics, bad habits, diseases and much more) - all this often contributes to the fact that vision can deteriorate over the years, i.e. the visual system begins to malfunction.

But vision deterioration in most cases is not an irreversible process - knowing certain techniques, this process you can reverse it and make your vision, if not the same as that of a baby (although this is sometimes possible), then as good as possible for each individual person. Therefore, the next lesson in our course on vision development will be devoted to methods of vision restoration.

Look at the root!

Test your knowledge

If you want to test your knowledge on the topic of this lesson, you can take a short test consisting of several questions. For each question, only 1 option can be correct. After you select one of the options, the system automatically proceeds to next question. The points you receive are affected by the correctness of your answers and the time spent on completion. Please note that the questions are different each time and the options are mixed.

Vision and hearing are much better developed in humans than the sense of smell. Light-sensitive cells and cells that detect sounds are collected in us, like in all highly developed animals, in special organs - the eyes and ears.

Like a camera, our eye has a “lens window” (cornea), a diaphragm (iris), an “adjustable lens” (lens) and a light-sensitive layer (the retina, which lies deep in the eye). Retinal cells send signals along the optic nerve to the cerebral cortex.

There are two types of light-sensitive cells in the human eye: rods and cones. The rods distinguish between dark and light. Cones perceive color. Cells of both types are located on the retina, which is thin and riddled with blood vessels. inner shell eyeball. In general, the eyeball consists of several dense layers of connective tissue that give it its shape.

Thanks to the lens, everything we see is reflected upside down on the retina. However, the brain corrects the distorted picture. In general, he easily adapts to everything. If someone decides to stand on his head for weeks on end, soon instead of upside-down pictures he will again begin to see normal, “put on his feet” images.

1. Optic nerve; 2. Muscle; 3. Frontal bone; 4. Cornea; 5. Muscle

The front part of the eyeball - the cornea - is transparent, like glass: it transmits light into the eye. The light is then captured by the eye's "diaphragm" - the iris - and collected into a beam. Pigment cells in the iris give the eyes a certain color. If there is a lot of pigment, the eyes are colored Brown color, if there is little or none of it - in greenish-gray and blue tones. The light then enters the pupil, a hole in the iris surrounded by two small muscles. In bright light, one muscle constricts the pupil, the other dilates it if it is dark. Having passed the pupil, the light rays fall directly on the lens - an elastic organ that constantly tries to take the shape of a ball. A ring of muscles interferes with it: they constantly stretch and reduce the convexity of the lens. So, the lens easily changes its curvature. Therefore, light rays fall precisely on the layer of the retina dotted with rods and cones, and we clearly see objects. When we look at objects that are close to us, the lens becomes convex and refracts rays more strongly, and when objects are far away from us, it becomes flatter and refracts rays weaker. With age, the lens loses elasticity. In order to somehow fix the problem, we have to help our natural lens- lens - and use glasses.

Like a camera, the eye is equipped with a “lens window,” a “diaphragm,” an “adjustable lens,” and a “photosensitive layer,” which resembles photographic film. Only this layer is part of the eye itself, its retina. And yet a person sees more than a camera. After all, he looks at the world with two eyes. Both the left and right eyes see objects differently. Our brain compares the two images received and judges the shape of what we see. That's why people have spatial vision. But, for example, a chicken’s eyes are set on the sides of its head, and it is not endowed with three-dimensional vision.

Myopia and farsightedness

Almost every third person suffers from visual impairment. Myopia and farsightedness are the most common, but can be corrected very well with glasses or contact lenses. Myopia occurs as a result of eye pathology. Myopic man can see clearly up close, but when looking into the distance the image becomes very blurry. Farsightedness is a consequence of normal aging of the eye. Starting at the age of 40, we see up close less and less clearly, as over the years the lens loses its flexibility.

The structure of the human eye is practically no different from the structure of many animals. In particular, the eyes of humans and octopuses have the same anatomy.

The human organ of vision is incredibly complex system, including a large number of elements. And if its anatomy has been disturbed, then this becomes the cause of vision deterioration. In the worst case, it causes absolute blindness.

Diagram of the structure of the human eye:

Human eye: external structure

The external structure of the eye is represented by the following elements:

The structure of the eyelid is quite complex. The eyelid protects the eye from negativity environment, preventing accidental injury. Presented by muscle tissue, outside protected skin, and from the inside - the mucous membrane, which is called the conjunctiva. It is this that ensures eye hydration and unhindered movement of the eyelid. Its outer outer edge is covered with eyelashes that perform a protective function.

The lacrimal department is represented by:

lacrimal gland. She is based in top corner outer part of the eye socket;
accessory glands. Placed inside the conjunctival membrane and near the upper edge of the eyelid;
drainage lacrimal ducts. Located on inside corners of the eyelids.

Tears serve two functions:

disinfect the conjunctival sac;
provide the necessary level of moisture to the surface of the cornea and conjunctiva.

The pupil occupies the center of the iris and is a round hole with a varying diameter (2 - 8 mm). Its expansion and contraction depends on illumination and occurs in automatic mode. It is through the pupil that light falls on the surface of the retina, which sends signals to the brain. The muscles of the iris are responsible for its work - expansion and contraction.

The cornea is represented by a completely transparent elastic membrane. It is responsible for maintaining the shape of the eye and is the main refractive medium. Anatomical structure The human cornea consists of several layers:

epithelial. Protects the eye, maintains the necessary level of moisture, ensures oxygen penetration;
Bowman's membrane. Eye protection and nutrition. Incapable of self-healing;
stroma. The main part of the cornea contains collagen;
Descemet's membrane. Acts as an elastic separator between the stroma and the endothelium;
endothelium. Responsible for the transparency of the cornea and also provides its nutrition. If damaged, it does not recover well, causing clouding of the cornea.

Sclera (white part) – opaque outer shell eyes. The lateral and posterior part of the eye is lined with the white surface, but in front it smoothly transforms into the cornea.

The structure of the sclera is represented by three layers:

episclera;
sclera substance;
dark scleral plate.

It includes nerve endings and an extensive network of blood vessels. The muscles responsible for the movement of the eyeball are supported (attached) by the sclera.

Human eye: internal structure

The internal structure of the eye is no less complex and includes:

lens;
vitreous body;
iris;
retina;
optic nerve.

Internal structure of the human eye:

The lens is another important refractive medium of the eye. It is responsible for focusing the image on its retina. The structure of the lens is simple: it is a completely transparent biconvex lens with a diameter of 3.5–5 mm with variable curvature.

The vitreous body is the largest spherical formation, filled with a gel-like substance that contains water (98%), protein and salts. It is completely transparent.

The iris of the eye is located directly behind the cornea, surrounding the opening of the pupil. It has the shape of a regular circle and is penetrated by many blood vessels.

The iris can have different shades. The most common is brown. Green, gray and blue eyes are more rare. Iris blue color is a pathology and appeared as a result of a mutation about 10 thousand years ago. Therefore, all people with blue eyes single ancestor.

The anatomy of the iris is represented by several layers:

border;
stromal;
pigment-muscular.

On its uneven surface there is a pattern characteristic of the eye of a particular person, created by pigmented cells.

The retina is one of the sections of the visual analyzer. External side it is adjacent to eyeball, and the inner one touches the vitreous body. The structure of the human retina is complex.

It has two parts:

visual, responsible for the perception of information;
blind (it completely lacks light-sensitive cells).

The work of this part of the eye is to receive, process and transform the light flux into an encrypted signal about the resulting visual image.

The retina is made up of special cells - cones and rods. At poor lighting The rods are responsible for the clarity of the picture. The duty of cones is to transmit color. The eye of a newborn baby in the first weeks of life does not distinguish color, since the formation of the cone layer in children is completed only by the end of the second week.

The optic nerve is represented by many intertwined nerve fibers, including the central canal of the retina. The thickness of the optic nerve is approximately 2 mm.

Table of the structure of the human eye and description of the functions of a specific element:

The importance of vision for a person cannot be overestimated. We receive this gift of nature as very young children, and our main task is to preserve it for as long as possible.

We invite you to watch a short video tutorial on the structure of the human eye.