External structure of the human eye. Structure of the human eye

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 it is human vision that 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. more 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 it seriously, you can conclude that the device visual system a person is “thought out” to the smallest detail by the Nature that created him. If you prefer to believe that the Creator or some other person is responsible for the creation of man Higher 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 that’s exactly what it does possible work about four dozen of its different components. 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 internal cavities eyes litter, dust and any 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 maximum quantity 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 surprising it is that such 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 the fact 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 the visual system is 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 a multilayered tissue sensitive to light covering back eyeball. The retina contains approximately 137,000,000 photoreceptors (for comparison, modern digital cameras, in which there are no more than 10,000,000 similar 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. Photosensitive 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 amazing is that the human eye can detect a few 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 incredibly 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 much is still unknown, but even that scientific world can provide today, 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 you know, 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 in 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.

It can be concluded that the brain is 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 that 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, the control and coordination of the communication of organs and tissues with the central nervous system through nerves (this is called innervation) of all 12 eye muscles represents 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 mobile eye that is phenomenal in terms of performance. 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,” so to speak, is provided, which consists of eyebrows, eyelids, eyelashes and tear glands.

The lacrimal glands regularly produce a sticky fluid, with slow speed moving down outer surface eyeball. This liquid washes away various debris (dust, etc.) from the cornea, after which it enters the internal tear duct 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 at the 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 a topic 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.

The human eye is often cited as an example of amazing natural engineering - but judging by the fact that this is one of 40 variants of devices that appeared in the process of evolution in different organisms, we should moderate our anthropocentrism and recognize that the structure of the human eye is not something then perfect.

It’s best to start the story about the eye with a photon. A quantum of electromagnetic radiation slowly flies directly into the eye of an unsuspecting passerby, who squints from the unexpected glare from someone’s watch.

The first part of the eye's optical system is the cornea. It changes the direction of light. This is possible due to such a property of light as refraction, which is also responsible for the rainbow. The speed of light is constant in vacuum - 300,000,000 m/s. But when moving from one medium to another (in this case, from air to the eye), light changes its speed and direction of movement. Air has a refractive index of 1.000293, and the cornea has a refractive index of 1.376. This means that the light beam in the cornea slows down by a factor of 1.376 and is deflected closer to the center of the eye.

A favorite way to split partisans is to shine a bright lamp in their face. This hurts for two reasons. Bright light is powerful electromagnetic radiation: Trillions of photons attack the retina, and its nerve endings are forced to transmit a frenzied number of signals to the brain. From overstrain, nerves, like wires, burn out. This forces the iris muscles to contract as hard as they can, desperately trying to close the pupil and protect the retina.

And flies up to the pupil. Everything is simple with it - it is a hole in the iris. Using the circular and radial muscles, the iris can constrict and dilate the pupil accordingly, regulating the amount of light entering the eye, like the diaphragm in a camera. The diameter of the human pupil can vary from 1 to 8 mm depending on the lighting.

Having flown through the pupil, the photon hits the lens - the second lens responsible for its trajectory. The lens refracts light weaker than the cornea, but it is mobile. The lens hangs on ciliary muscles, which change its curvature, thereby allowing us to focus on objects at different distances from us.

Visual impairment is associated with focus. The most common are myopia and farsightedness. In both cases, the image is not focused on the retina, as it should, but in front of it (myopia) or behind it (farsightedness). This is due to the eye, which changes shape from round to oval, and then the retina moves away from the lens or approaches it.

After the lens, the photon flies through the vitreous body (transparent jelly - 2/3 of the volume of the entire eye, 99% is water) straight to the retina. Here photons are detected and arrival messages are sent along nerves to the brain.

The retina is lined with photoreceptor cells: when there is no light, they produce special substances - neurotransmitters, but as soon as a photon hits them, the photoreceptor cells stop producing them - and this is a signal to the brain. There are two types of these cells: rods, which are more sensitive to light, and cones, which are better at detecting movement. We have about one hundred million rods and another 6-7 million cones, in total more than one hundred million light-sensitive elements - that’s more than 100 megapixels, which no “Hassel” could ever dream of.

The blind spot is a breakthrough point where there are no light-sensitive cells at all. It is quite large - 1-2 mm in diameter. Fortunately, we have binocular vision and a brain that combines two pictures with spots into one normal one.

At the moment of signal transmission, a problem with logic arises in the human eye. The underwater resident octopus, which does not particularly need vision, is much more consistent in this sense. In octopuses, a photon first hits the layer of cones and rods on the retina, immediately behind which a layer of neurons waits and transmits the signal to the brain. In humans, light first breaks through layers of neurons - and only then hits the photoreceptors. Because of this, there is a first spot in the eye - a blind spot.

The second spot is yellow, this is the central area of the retina directly opposite the pupil, just above the optic nerve. The eye sees best in this place: the concentration of light-sensitive cells here is greatly increased, so our vision in the center of the visual field is much sharper than the peripheral one.

The image on the retina is inverted. The brain knows how to correctly interpret the picture, and restores the original image from the inverted one. Children see everything upside down for the first couple of days while their brain installs its Photoshop. If we put on glasses that reverse the image (this was first done back in 1896), then after a couple of days our brain will learn to interpret such an inverted picture correctly.

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The eye is paired organ visual system that perceives electromagnetic radiation in the light range.

Almost 90% of all information is perceived by us through vision.

The human eye consists of the following sections:

Retina. Primary department optic nerve. Here a nerve impulse is formed and sent along the further visual pathway;
Vitreous body. It appears as a jelly-like mass that refracts light;
Lens. This is a lens that is adjusted by the ciliary muscle and allows you to see objects near and far equally well;
Iris and pupil. This is a fluid-filled cavity located under the cornea. Behind it is the iris, which is shaped like a ring. It consists of connective tissue, muscle and pigment cells that give the eyes their color. Depending on the flow of light, it can narrow or expand. The hole that is inside is the pupil;
Cornea. It is located in the front of the eye and is a transparent convex plate;
Conjunctiva. This is a thin membrane that covers the surface of the eye.

The eye is nourished by vessels located directly behind the retina.

Human eye diagram:

Structure of the human eye

Eye capsule - outer shell the eyeball, the main part of which is formed by the sclera (5/6 of the plane), the smaller part is the cornea.

Sclera- a dense, fibrous membrane, poor in cellular elements and blood vessels, in front gradually passes into the cornea. In this case, the inner and middle layers of the sclera turn into a transparent cornea earlier than the outer ones, through which the deep transparent layers are visible.

IN superficial sections sclera, its border with the cornea is a translucent belt - the area where the sclera transitions to the cornea. This is the limbus. The normal width of the limba is 1.5–2 mm.

The cornea has a convex shape, with a diameter of 10–11 mm.

Cornea- the anterior, convex part of the outer fibrous capsule of the eye. It is spherical, without vessels, shiny, transparent and very sensitive. The cornea has a convex shape, with a diameter of 10–11 mm.

The vascular tract consists of the following sections: the iris, ciliary body and choroid. It is located in the middle between the sclera and loose tissue with numerous slits, separated from it by space for the outflow of intraocular fluid.

Iris– the lens located in front separates the anterior and posterior chambers (displays). In its center there is a pupil. It reacts to light, and thanks to this, the iris regulates the flow of light to the light-sensitive apparatus.

Iris with ciliary body- This is the organ of formation of intraocular fluid. The connection of the ciliary body with the lens of the eye leads to their working together in the act of accommodation.

The retina performs the function of light perception. It extends to the ciliary body and iris by double-layered epithelium. The optical part of the retina is very firmly fixed in the area of the optic nerve head.

The remaining areas are tightly adjacent to the vitreous plate. Well connected to the rod and cone layers. These two layers are connected to each other and to other elements of the retina (more loosely). Despite the fact that the pigment epithelium belongs to the retina, it is anatomically connected specifically to the choroid.

The retina is thin, almost transparent. Functionally, the retina is divided into two layers: the light-sensitive (external) and the light-conducting (cerebral) layers, consisting of three neurons.

Rods and cones– light-sensitive photoreceptors or visual cells. They consist of external and internal segments and fibers with a nucleus and have pigments: rhodopsin in rods and iodopsin in cones. The number of cones is seven million, rods about 130 million.

There are no optic cells in the area of the optic nerve head, here is the functional optically inactive zone - . At a distance of 4 mm from the outside of the disc, there is a yellow spot with a central depression - a fossa, where only the cones are located.

This is the functional center of the retina with high visual ability. Up close macular spot, each cone is surrounded by one row of rods. Between the cones there are already 2–4 rods, and towards the periphery the number of rods increases, and the number of cones decreases.

Physiological role the retina is determined by its photosensitive and light-conducting functions.

Of the elements of retinal tissue, the most pigmented epithelium is involved in the formation of visual purple.

It plays a role in vision by absorbing light rays that unnecessarily irritate the retina; prevents scattering of rays and directs the light, similar to the action of a reflector.

Rods and cones have different functions. Rods are the elements for determining the intensity of light, and cones are responsible for the qualitative perception of object shapes, brightness and color.

This heterogeneity of the retina leads to a functional difference between its center and periphery. The peculiarities of the combination of rods and cones with special cells lead to the fact that a single cone has its place in nervous system. But sticks do not have such representation. This gives clarity to images and the perception of the shape of objects (properties of the macula areas).

At the periphery, where there are more rods, irritation enters the brain through one conductor from a group of cells that occupy a large area. Yes, it is ensured high sensitivity retina to low light, with simultaneous blur visual perception items.

Now you know the structure of the eyeball, but how do we get a picture in our heads?

Image acquisition process

The unique optical system of the eye allows you to obtain a clear image of objects. Light rays pass through all parts of the eye and are refracted in them according to the laws of optics.

The main role in obtaining the image is played by the lens. In order for objects to be clearly visible, their image must be focused in the center of the retina. Due to the fact that the lens can change its curvature, thereby changing the refractive power of the eye, a person can see objects equally well both at close and far distances. This process is called accommodation.

Rays of light pass through optical system eyes, are processed and transmitted to central departments visual system. The retina consists of 3 layers:

The first (pigment), absorbs light rays and allows you to clearly see objects;
The second layer (photoreceptors) perceives light and converts its energy into visual impulses;
Third layer ( nerve cells connected to photoreceptors). Through it, information is transmitted to the cerebral cortex (visual areas), where it is analyzed.

The most popular causes of visual impairment

Vision may deteriorate for the following reasons:

The human eye is a complex optical system consisting of many functional elements. Thanks to their coordinated work, we perceive 90% of incoming information, that is, the quality of our life largely depends on vision. Knowing the structure of the eye will help us better understand how it works and the importance of the health of each element of its structure.

Many people remember how human eyes work from school. The main parts are the cornea, iris, pupil, lens, retina, macula and optic nerve. Muscles approach the eyeball, providing them with coordinated movement, and for a person - high-quality surround vision. How do all these elements interact with each other?

The structure of the human eye: a view from the inside

The eye structure resembles a powerful lens that collects rays of light. This function is performed by the cornea - the anterior transparent layer of the eye. Interestingly, its diameter increases from birth to 4 years, after which it does not change, although the apple itself continues to grow. This is why young children's eyes appear larger than adults'. Having passed through it, the light reaches the iris - the light-proof diaphragm of the eye, in the center of which there is a hole - the pupil. Thanks to its ability to contract and expand, our eye can quickly adapt to light of different intensities. From the pupil, rays fall on a biconvex lens - the lens. Its function is to refract rays and focus the image. The lens is playing important role as part of a light-refracting apparatus, since it is able to tune in to the vision of objects located at different distances from a person. This arrangement of the eye allows us to see well both near and far.

Many of us remember parts like this from school. human eye, such as the cornea, pupil, iris, lens, retina, macula and optic nerve. What is their purpose?

Upside Down World

From the pupil, rays of light reflected from objects are projected onto the retina of the eye. It represents a kind of screen on which the image of the surrounding world is “transmitted”. Interestingly, it is initially upside down. Thus, land and trees are transferred to top part retina, sun and clouds - on the bottom. What our gaze is currently directed at is projected onto the central part of the retina (fovea). It, in turn, is the center of the macula, or macula zone. It is this area of the eye that is responsible for clear central vision. Anatomical features The fovea determines its high resolution. A person has one central fovea, a hawk has two in each eye, and, for example, in cats it is represented by a long visual stripe. This is why the vision of some birds and animals is sharper than ours. Thanks to this device, our eyes clearly see even small objects and details, and also distinguish colors.

Rods and cones

It is worth mentioning separately the photoreceptors of the retina - rods and cones. They help us see. Cones are responsible for color vision. They are mainly concentrated in the center of the retina. Their sensitivity threshold is higher than that of sticks. With the help of cones, we see colors provided there is sufficient lighting. Rods are also located in the retina, but their concentration is maximum at its periphery. These photoreceptors are active in dim lighting. It is thanks to them that we can distinguish objects in the dark, but we do not see their color, since the cones remain inactive.

Miracle of sight

In order for us to see the world “correctly”, the brain must connect to the work of the eye. Therefore, the information that was collected by the light-sensitive cells of the retina is transmitted optic nerve. To do this, it is converted into electrical impulses. By nerve tissues they are transmitted from the eye to the human brain. This is where the analysis work begins. The brain processes the incoming information, and we perceive the world as it is - the sun in the sky above, and the earth under our feet. To check this fact, you can put special glasses on your eyes that reverse the image. After some time, the brain will adapt, and the person will again see the picture from his usual perspective.

As a result of the processes described, our eyes are able to see the world around us in all its fullness and brightness!

Undoubtedly, each of the senses is important and necessary for a person to fully perceive the world around him.

Vision allows people to see the world as it is - bright, diverse, unique.

Organ - vision

In the human organ - vision - we can distinguish the following components:

Peripheral zone - responsible for correct perception source data. In turn, it is divided into:
- eyeball;
- protection system;
- adnexal system;
- motor system.
The area responsible for conducting nerve signals.
Subcortical centers.
Cortical visual centers.

Anatomy of the human eye structure

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

Outer shell of the eye presented connective tissue. The anterior zone is called the cornea and has a transparent structure. Back zone- sclera, better known as protein. Thanks to the outer shell, the shape of the eye is round.

Cornea. A small part of the outer layer. The shape resembles an ellipse, the dimensions of which are as follows: horizontal - 12 mm, vertical - 11 mm. The thickness of this part of the eye does not exceed one millimeter. Distinctive feature corneas – complete absence blood vessels. The cells of the cornea form a clear order, which is what makes it possible to see the picture undistorted and clear. The cornea is a convex-concave lens with a refractive power of approximately forty diopters. The sensitivity of this area of the fibrous layer is very significant. This is explained by the fact that the zone is the location of nerve endings.

Sclera (protein). It is opaque and durable. The composition includes fibers that have an elastic structure. The muscles of the eye are attached to the protein.

Middle layer of the eye. Presented blood vessels and is divided by ophthalmologists into the following zones:

iris;
ciliary body or ciliary body;
choroid.

Iris. A circle in the center of which, in a special hole, the pupil is located. The muscles located inside the iris allow the pupil to change in diameter. This happens when they contract and relax. It is important to note that the designated zone determines the shade of human eyes.

Ciliary or ciliary body. Location: central zone of the middle ocular membrane. Outwardly it looks like a circular roller. The structure is slightly thickened.

The vascular part of the eye - processes, carry out the formation of ocular fluid. Special ligaments attached to the vessels, in turn, fix the lens.

Choroid. Posterior zone of the medial shell. It is represented by arteries and veins, with their help the other parts of the eye are fed.

Inner lining of the eye– retina. The thinnest of all three shells. Presented different types cells: rods and cones.

It should be noted that peripheral and twilight vision humans are possible due to the fact that the shell contains rods and are highly photosensitivity.

Cones are responsible for central vision. In addition, thanks to cones, a person has the ability to distinguish colors. The maximum concentration of these cells occurs in the macula or corpus luteum. The main function of this zone is to ensure visual acuity.

Ocular nucleus (eye cavity). The core consists of the following components:

fluid that fills the chambers of the eye;
lens;
vitreous body.

The anterior chamber is located between the iris and cornea. The cavity between the lens and the iris is the posterior chamber. The two cavities have the ability to interact using the pupil. Thanks to this, intraocular fluid easily circulates between the two cavities.

Lens. One of the components of the ocular nucleus. Located in a transparent capsule, the location of which is the anterior zone of the vitreous body. Externally similar to a biconvex lens. Power is supplied through intraocular fluid. Ophthalmology identifies several important components lens:

capsule;
capsular epithelium;
lens substance.

Over the entire surface, the lens and vitreous body are separated from each other the thinnest layer liquids.

Vitreous body. Occupies the largest part of the eye. The consistency resembles a gel. Main components: water and hyaluronic acid. Provides nutrition to the retina and is part of the optical system of the eye. The vitreous body consists of three components:

the vitreous body itself;
limiting membrane;
Klyuev channel.

In this video you will see the principle of the human eye.

Eye protection system

Eye socket. Niche formed bone tissue, where the eye is directly located. In addition to the eyeball, it consists of:

optic nerves;
vessels;
fat;
muscles.

Eyelids. Folds formed by skin. The main task is to protect the eyes. Thanks to the eyelids, the eye is protected from mechanical damage and hits foreign bodies. In addition, the eyelids distribute intraocular fluid over the entire surface of the eye. The skin of the eyelids is very thin. Over the entire surface of the eyelids with inside the conjunctiva is located.

Conjunctiva. Mucous membrane of the eyelids. Location: anterior zone of the eye. Gradually transforms into conjunctival sacs without affecting the cornea of the eye. In the closed position of the eyes, with the help of the conjunctival leaves, a hollow space is formed, protecting against drying out and mechanical damage.

Lacrimal system of the eye

Includes several components:

lacrimal gland;
lacrimal sac;
nasolacrimal duct.

The lacrimal gland is located near the outer edge of the orbit, in the upper zone. The main function is the synthesis of tear fluid. Subsequently, the liquid follows excretory ducts and, washing the outer surface of the eye, accumulates in the conjunctival sac. At the last stage, fluid is collected in the lacrimal sac.

Muscular apparatus of the eye

The rectus and oblique muscles are responsible for eye movement. The muscles originate in the orbit. Following along the entire eye, the muscles end in the white.

In addition, this system contains muscles that allow the eyelids to close and open - the levator palpebral muscle and the orbicularis or orbital muscle.