Passage of light through the eye. The structure and functions of the human organs of vision. Eyeball and auxiliary apparatus. Huge amount of detail

, lens and vitreous body. Their combination is called diopter apparatus. Under normal conditions, refraction (refraction) of light rays from the visual target by the cornea and lens occurs, so that the rays are focused on the retina. The refractive power of the cornea (the main refractive element of the eye) is 43 diopters. The convexity of the lens can vary, and its refractive power varies between 13 and 26 diopters. Due to this, the lens provides accommodation of the eyeball to objects that are at close or far distances. When, for example, rays of light from a distant object enter a normal eye (with a relaxed ciliary muscle), the target appears on the retina in focus. If the eye is directed to a nearby object, they focus behind the retina (i.e., the image on it is blurred) until accommodation occurs. The ciliary muscle contracts, loosening the tension of the girdle fibers; the curvature of the lens increases, and as a result, the image is focused on the retina.

The cornea and lens together form a convex lens. Rays of light from an object pass through the nodal point of the lens and form an inverted image on the retina, as in a camera. The retina can be compared to photographic film because both of them capture visual images. However, the retina is much more complex. It processes a continuous sequence of images, and also sends messages to the brain about the movements of visual objects, threatening signs, periodic changes in light and dark, and other visual data about the external environment.

Although the optical axis of the human eye passes through the nodal point of the lens and the point of the retina between the fovea and the optic nerve head (Fig. 35.2), the oculomotor system orients the eyeball to the site of the object, called the fixation point. From this point, a beam of light passes through the nodal point and is focused in the fovea; thus, it runs along the visual axis. The rays from the rest of the object are focused in the area of ​​the retina around the fovea (Fig. 35.5).

The focusing of rays on the retina depends not only on the lens, but also on the iris. The iris acts as the diaphragm of a camera and regulates not only the amount of light entering the eye, but, more importantly, the depth of the visual field and the spherical aberration of the lens. With a decrease in pupil diameter, the depth of the visual field increases and the light rays are directed through the central part of the pupil, where spherical aberration is minimal. Changes in the diameter of the pupil occur automatically (i.e. reflexively) when adjusting (accommodating) the eye to viewing close objects. Therefore, during reading or other eye activities associated with the discrimination of small objects, the image quality is improved by the optical system of the eye.

Image quality is affected by another factor - light scattering. It is minimized by limiting the beam of light, as well as its absorption by the pigment of the choroid and the pigment layer of the retina. In this respect, the eye again resembles a camera. There too, scattering of light is prevented by confining the beam of rays and absorbing it by the black paint covering the inner surface of the chamber.

Focusing of the image is disturbed if the size of the pupil does not match the refractive power of the diopter apparatus. With myopia (myopia), images of distant objects are focused in front of the retina, not reaching it (Fig. 35.6). The defect is corrected with concave lenses. Conversely, with hypermetropia (farsightedness), images of distant objects are focused behind the retina. To eliminate the problem, convex lenses are needed (Fig. 35.6). True, the image can be temporarily focused due to accommodation, but the ciliary muscles get tired and the eyes get tired. With astigmatism, asymmetry occurs between the radii of curvature of the surfaces of the cornea or lens (and sometimes the retina) in different planes. For correction, lenses with specially selected radii of curvature are used.

The elasticity of the lens gradually decreases with age. Decreases the efficiency of his accommodation when looking at close objects (presbyopia). At a young age, the refractive power of the lens can vary over a wide range, up to 14 diopters. By the age of 40, this range is halved, and after 50 years - up to 2 diopters and below. Presbyopia is corrected with convex lenses.

Equipment: collapsible model of the eye, table "Visual analyzer", three-dimensional objects, reproductions of paintings. Handouts for desks: drawings "The structure of the eye", cards for fixing on this topic.

During the classes

I. Organizational moment

II. Checking students' knowledge

1. Terms (on the board): sense organs; analyzer; the structure of the analyzer; types of analyzers; receptors; nerve pathways; think tank; modality; areas of the cerebral cortex; hallucinations; illusions.

2. Additional homework information (student messages):

– for the first time we meet the term “analyzer” in the works of I.M. Sechenov;
- per 1 cm of skin from 250 to 400 sensitive endings, on the surface of the body there are up to 8 million of them;
- about 1 billion receptors are located on the internal organs;
- THEM. Sechenov and I.P. Pavlov believed that the activity of the analyzer is reduced to the analysis of the effects on the body of the external and internal environment.

III. learning new material

(Message of the topic of the lesson, goals, objectives and motivation of students' learning activities.)

1. The meaning of vision

What is the meaning of vision? Let's answer this question together.

Yes, indeed, the organ of vision is one of the most important sense organs. We perceive and cognize the world around us primarily with the help of vision. So we get an idea about the shape, size of the object, its color, notice the danger in time, admire the beauty of nature.

Thanks to vision, a blue sky opens before us, young spring foliage, bright colors of flowers and butterflies fluttering above them, a golden field of fields. Wonderful autumn colors. We can admire the starry sky for a long time. The world around us is beautiful and amazing, admire this beauty and take care of it.

It is difficult to overestimate the role of vision in human life. The thousand-year experience of mankind is passed down from generation to generation through books, paintings, sculptures, architectural monuments, which we perceive with the help of vision.

So, the organ of vision is vital for us, with the help of it a person receives 95% of information.

2. Eye position

Consider the drawing in the textbook and establish which bone processes are involved in the formation of the eye socket. ( Frontal, zygomatic, maxillary.)

What is the role of the eye sockets?

And what helps to turn the eyeball in different directions?

Experiment No. 1. The experiment is carried out by students sitting at the same desk. One needs to follow the movement of the pen at a distance of 20 cm from the eye. The second one moves the handle up-down, right-left, describes a circle with it.

How many muscles move the eyeball? ( At least 4, but there are 6 in total: four straight and two oblique. Due to the contraction of these muscles, the eyeball can rotate in the orbit.)

3. Eye protectors

Experience number 2. Watch your neighbor's eyelids blink and answer the question: what is the function of the eyelids? ( Protection against light irritation, protection of the eyes from foreign particles.)

Eyebrows trap the sweat flowing from the forehead.

Tears have a lubricating and disinfecting effect on the eyeball. The lacrimal glands - a kind of "tears factory" - open under the upper eyelid with 10-12 ducts. Tears are 99% water and only 1% salt. This is a wonderful eyeball cleaner. Another function of tears has also been established - they remove dangerous poisons (toxins) from the body, which are produced at the time of stress. In 1909, the Tomsk scientist P.N. Lashchenkov discovered a special substance in the lacrimal fluid, lysozyme, capable of killing many microbes.

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4. The structure of the visual analyzer

We see only when there is light. The sequence of rays passing through the transparent medium of the eye is as follows:

light beam → cornea → anterior chamber of the eye → pupil → posterior chamber of the eye → lens → vitreous body → retina.

The image on the retina is reduced and inverted. However, we see objects in their natural form. This is due to the life experience of a person, as well as the interaction of signals from all the senses.

The visual analyzer has the following structure:

1st link - receptors (rods and cones on the retina);
2nd link - optic nerve;
3rd link - brain center (occipital lobe of the brain).

The eye is a self-adjusting device, it allows you to see near and distant objects. Even Helmholtz believed that the model of the eye is a camera, the lens is the transparent refractive media of the eye. The eye is connected to the brain through the optic nerve. Vision is a cortical process, and it depends on the quality of information coming from the eye to the centers of the brain.

Information from the left side of the visual fields from both eyes is transmitted to the right hemisphere, and from the right side of the visual fields of both eyes to the left.

If the image from the right and left eyes enters the corresponding brain centers, then they create a single three-dimensional image. Binocular vision - vision with two eyes - allows you to perceive a three-dimensional image and helps determine the distance to an object.

Table. The structure of the eye

5. Conclusions

1. A person perceives light with the help of the organ of vision.

2. Light rays are refracted in the optical system of the eye. A reduced reverse image is formed on the retina.

3. The visual analyzer includes:

- receptors (rods and cones);
- nerve pathways (optic nerve);
- brain center (occipital zone of the cerebral cortex).

IV. Consolidation. Working with handouts

Exercise 1. Set a match.

1. Lens. 2. Retina. 3. Receptor. 4. Pupil. 5. Vitreous body. 6. Optic nerve. 7. Protein membrane and cornea. 8. Light. 9. Vascular membrane. 10. Visual area of ​​the cerebral cortex. 11. Yellow spot. 12. Blind spot.

A. Three parts of the visual analyzer.
B. Fills the inside of the eye.
B. Cluster of cones in the center of the retina.
G. Changes curvature.
D. Carries out various visual stimuli.
E. Protective membranes of the eye.
G. Place of exit of the optic nerve.
3. Imaging site.
I. Hole in the iris.
K. Black nourishing layer of the eyeball.

(Answer: A - 3, 6, 10; B - 5; AT 11; G - 1; D - 8; E - 7; W -12; Z - 2; I - 4; K - 9.)

Task 2. Answer the questions.

How do you understand the expression “The eye looks, but the brain sees”? ( In the eye, only excitation of receptors occurs in a certain combination, and we perceive the image when the nerve impulses reach the zone of the cerebral cortex.)

The eyes feel neither heat nor cold. Why? ( There are no heat and cold receptors in the cornea.)

Two students argued: one argued that the eyes get more tired when looking at small objects that are close, and the other - distant objects. Which of them is right? ( The eyes get tired more when looking at objects that are close, as this greatly strains the muscles that ensure the work (increase in curvature) of the lens. Looking at distant objects is a rest for the eyes.)

Task 3. Sign the structural elements of the eye indicated by numbers.

Literature

Vadchenko N.L. Test your knowledge. Encyclopedia in 10 volumes. T. 2. - Donetsk, ICF "Stalker", 1996.
Zverev I.D. Reading book on human anatomy, physiology and hygiene. – M.: Enlightenment, 1983.
Kolesov D.V., Mash R.D., Belyaev I.N. Biology. Human. Textbook for 8 cells. – M.: Bustard, 2000.
Khripkova A.G. Natural science. – M.: Enlightenment, 1997.
Sonin N.I., Sapin M.R. Human biology. – M.: Bustard, 2005.

Photo from the site http://beauty.wild-mistress.ru

Separate parts of the eye (cornea, lens, vitreous body) have the ability to refract the rays passing through them. WITH eye physics point of view yourself an optical system capable of collecting and refracting rays.

refractive the strength of individual parts (lenses in the device re) and the entire optical system of the eye is measured in diopters.

Under one diopter is understood as the refractive power of a lens whose focal length is 1 m. If refractive power increases, focal length shortens struggles. From here it follows that a lens with a focal length a distance of 50 cm will have a refractive power of 2 diopters (2 D).

The optical system of the eye is very complex. It suffices to point out that there are only several refractive media, and each medium has its own refractive power and structural features. All this makes it extremely difficult to study the optical system of the eye.

Rice. Building an image in the eye (explained in the text)

The eye is often compared to a camera. The role of the camera is played by the cavity of the eye, darkened by the choroid; The retina is the photosensitive element. The camera has a hole in which the lens is inserted. Rays of light entering the hole pass through the lens, refract and fall on the opposite wall.

The optical system of the eye is a refractive collecting system. It refracts the rays passing through it and again gathers them into one point. Thus, a real image of a real object appears. However, the image of the object on the retina is reversed and reduced.

To understand this phenomenon, let us turn to the schematic eye. Rice. gives an idea of ​​the course of rays in the eye and obtaining an inverse image of an object on the retina. The beam departing from the upper point of the object, indicated by the letter a, passing through the lens, is refracted, changes direction and occupies the position of the lower point on the retina, indicated in the figure A 1 The beam from the lower point of the object B, refracting, falls on the retina as the upper point in 1 . Rays from all points fall in the same way. Consequently, a real image of the object is obtained on the retina, but it is reversed and reduced.

So, calculations show that the size of the letters of this book, if when reading it is at a distance of 20 cm from the eye, on the retina will be 0.2 mm. the fact that we see objects not in their inverted image (upside down), but in their natural form, is probably due to accumulated life experience.

A child in the first months after birth confuses the upper and lower sides of the object. If such a child is shown a burning candle, the child, trying to grab the flame, stretches out his hand not to the upper, but to the lower end of the candle. By controlling the indications of the eye with the hands and other sense organs in the course of later life, a person begins to see objects as they are, despite their reverse image on the retina.

Eye accommodation. A person cannot simultaneously see objects that are at different distances from the eye equally clearly.

In order to see an object well, it is necessary that the rays emanating from this object are collected on the retina. Only when the rays fall on the retina do we see a clear image of the object.

The adaptation of the eye to receive distinct images of objects at different distances is called accommodation.

In order to obtain a clear image in every caseing, it is necessary to change the distance between the refractive lens and the rear wall of the camera. This is how the camera works. To get a clear image on the back of the camera, move the lens back or zoom in. According to this principle, accommodation occurs in fish. In them, the lens with the help of a special device moves away or approaches the back wall of the eye.

Rice. 2 CHANGE IN THE CURVATURE OF THE LENS IN ACCOMMODATION 1 - lens; 2 - lens bag; 3 - ciliary processes. The top figure is an increase in the curvature of the lens. The ciliary ligament is relaxed. Lower figure - the curvature of the lens is reduced, the ciliary ligaments are stretched.

However, a clear image can also be obtained if the refractive power of the lens changes, and this is possible by changing its curvature.

According to this principle, accommodation occurs in humans. When seeing objects at different distances, the curvature of the lens changes and due to this, the point where the rays converge approaches or moves away, each time falling on the retina. When a person examines close objects, the lens becomes more convex, and when considering distant objects, it becomes flatter.

How does the curvature of the lens change? The lens is in a special transparent bag. The curvature of the lens depends on the degree of tension of the bag. The lens has elasticity, so when the bag is stretched, it flattens out. When the bag is relaxed, the lens, due to its elasticity, acquires a more convex shape (Fig. 2). The change in the tension of the bag occurs with the help of a special circular accommodative muscle, to which the ligaments of the capsule are attached.

With the contraction of the accommodation muscles, the ligaments of the lens bag weaken and the lens acquires a more convex shape.

The degree of change in the curvature of the lens also depends on the degree of contraction of this muscle.

If an object located at a distant distance is gradually brought closer to the eye, then accommodation begins at a distance of 65 m. As the object approaches the eye further, the accommodative efforts increase and at a distance of 10 cm are exhausted. Thus, the point of near vision will be at a distance of 10 cm. With age, the elasticity of the lens gradually decreases, and consequently, the ability to accommodate also changes. The nearest point of clear vision for a 10-year-old is at a distance of 7 cm, for a 20-year-old - at a distance of 10 cm, for a 25-year-old - 12.5 cm, for a 35-year-old - 17 cm, for a 45-year-old - 33 cm, in a 60-year-old - 1 m, in a 70-year-old - 5 m, in a 75-year-old the ability to accommodate is almost lost and the nearest point of clear vision moves to infinity.

The lens and the vitreous body. Their combination is called a diopter apparatus. Under normal conditions, light rays are refracted (refracted) from a visual target by the cornea and lens, so that the rays are focused on the retina. The refractive power of the cornea (the main refractive element of the eye) is 43 diopters. The convexity of the lens can vary, and its refractive power varies between 13 and 26 diopters. Due to this, the lens provides accommodation of the eyeball to objects that are at close or far distances. When, for example, rays of light from a distant object enter a normal eye (with a relaxed ciliary muscle), the target appears on the retina in focus. If the eye is directed to a nearby object, they focus behind the retina (i.e., the image on it is blurred) until accommodation occurs. The ciliary muscle contracts, loosening the tension of the girdle fibers; the curvature of the lens increases, and as a result, the image is focused on the retina.

The cornea and lens together make up a convex lens. Rays of light from an object pass through the nodal point of the lens and form an inverted image on the retina, as in a camera. The retina can be compared to photographic film because both of them capture visual images. However, the retina is much more complex. It processes a continuous sequence of images, and also sends messages to the brain about the movements of visual objects, threatening signs, periodic changes in light and darkness, and other visual data about the external environment.

Although the optical axis of the human eye passes through the nodal point of the lens and the point of the retina between the fovea and the optic nerve head (Fig. 35.2), the oculomotor system orients the eyeball to the site of the object, called the fixation point. From this point, a beam of light passes through the nodal point and is focused in the fovea; thus, it runs along the visual axis. The rays from the rest of the object are focused in the retinal area around the fovea (Fig. 35.5).

The focusing of rays on the retina depends not only on the lens, but also on the iris. The iris acts as the diaphragm of a camera and regulates not only the amount of light entering the eye, but, more importantly, the depth of the visual field and the spherical aberration of the lens. With a decrease in pupil diameter, the depth of the visual field increases and the light rays are directed through the central part of the pupil, where spherical aberration is minimal. Changes in the diameter of the pupil occur automatically (i.e. reflexively) when adjusting (accommodating) the eye to viewing close objects. Therefore, during reading or other eye activities associated with the discrimination of small objects, the image quality is improved by the optical system of the eye.

Image quality is affected by another factor - light scattering. It is minimized by limiting the beam of light, as well as its absorption by the pigment of the choroid and the pigment layer of the retina. In this respect, the eye again resembles a camera. There too, scattering of light is prevented by confining the beam of rays and absorbing it by the black paint covering the inner surface of the chamber.

Focusing of the image is disturbed if the size of the pupil does not match the refractive power of the diopter apparatus. With myopia (myopia), images of distant objects are focused in front of the retina, not reaching it (Fig. 35.6). The defect is corrected with concave lenses. Conversely, with hypermetropia (farsightedness), images of distant objects are focused behind the retina. To fix the problem, convex lenses are needed (Fig. 35.6). True, the image can be temporarily focused due to accommodation, but the ciliary muscles get tired and the eyes get tired. With astigmatism, asymmetry occurs between the radii of curvature of the surfaces of the cornea or lens (and sometimes the retina) in different planes. For correction, lenses with specially selected radii of curvature are used.

The elasticity of the lens gradually decreases with age. Decreases the efficiency of his accommodation when looking at close objects (presbyopia). At a young age, the refractive power of the lens can vary over a wide range, up to 14 diopters. By the age of 40, this range is halved, and after 50 years - up to 2 diopters and below. Presbyopia is corrected with convex lenses.

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 sight, we would most likely just live in darkness.

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 at a variety of distances, regulate the amount of incoming light, distinguish between a huge number of colors and even more shades, correct spherical and chromatic aberrations, etc. Associated with the brain of the eye are six levels of the retina, in which even before the information is sent to the brain, the data passes through the compression stage.

But how is our vision arranged? How, by amplifying the color reflected from objects, do we transform it into an image? If we think about it seriously, we can conclude that the device 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 Higher Power is responsible for the creation of man, then you can attribute this merit to them. But let's not understand, but continue the conversation about the device of vision.

Huge amount of detail

The structure of the eye and its physiology can be called truly ideal. Think for yourself: both eyes are in the bony sockets of the skull, which protect them from all kinds of damage, but they protrude from them just so that the widest possible horizontal view is provided.

The distance at which the eyes are apart 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 think of what would happen if our eyes were square or triangular or their movement would be chaotic - this would make vision limited, chaotic and ineffective.

So, the structure of the eye is extremely complicated, but this is precisely what makes it possible for about four dozen of its various components to work. And even if there were not even one of these elements, the process of seeing would cease to be carried out as it should be carried out.

To see how complex the eye is, we suggest you turn your 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.

The passage of light

As light approaches the eye, the light rays collide with the cornea (otherwise known as the cornea). The transparency of the cornea allows light to pass through it into the inner surface of the eye. Transparency, by the way, is the most important characteristic of the cornea, and it remains transparent due to the fact that a special protein that it contains inhibits the development of blood vessels - a process that occurs in almost every tissue of the human body. In the event that the cornea was not transparent, the other components of the visual system would not matter.

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

After the 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 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 change directly with the iris, and this is due to its unique structure, because it consists of two different types of muscle tissue (even here there are muscles!). The first muscle is circular compressive - 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 the muscle. The second muscle is expanding - it is located radially, i.e. along the radius of the iris, which can be compared with the spokes in the wheel. In dark light, this second muscle contracts, and the iris opens the pupil.

Many people still experience some difficulties when they try to explain how the above-mentioned elements of the human visual system are formed, because in any other intermediate form, i.e. at any evolutionary stage, they simply could not work, but a person sees from the very beginning of his existence. Mystery…

Focusing

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

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

It is important to note that the unique structure and composition provides the cornea and lens with a high refractive power, which guarantees a short focal length. And how amazing that such a complex system fits in just one eyeball (just think how a person could look like if, for example, a meter would be required to focus the 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 proportion 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 speak of as something that only happened through stepwise 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 here it is still more curious, because in this situation the refraction of light rays is even stronger. This is provided by an increase in the curvature of the lens. The lens is connected by means of ciliary bands to the ciliary muscle, which, by contracting, allows the lens to take on a more convex shape, thereby increasing its refractive power.

And here again it is impossible not to mention the most complex structure of the lens: it consists of many threads, which consist of cells connected to each other, and thin bands connect it with the ciliary body. Focusing is carried out under the control of the brain extremely quickly and on a full "automatic" - it is impossible for a person to carry out such a process consciously.

The meaning of "film"

Focusing results in focusing the image on the retina, which is a multi-layered, light-sensitive tissue that covers the back of the eyeball. The retina contains approximately 137,000,000 photoreceptors (for comparison, modern digital cameras can be cited, in which there are 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 - about 400,000 per 1 mm².

It would not be superfluous to quote here the words of microbiologist Alan L. Gillen, who speaks in his book "Body by Design" of the retina 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 man-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 of them. But even more amazing is that the human eye can pick up 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. 2 types of photoreceptors have a special shape, 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 receptive to light, but are able to distinguish colors - the optimal work of cones is noted in the daytime.

Thanks to the work of photoreceptors, light rays are transformed into complexes of electrical impulses and sent to the brain at an incredibly high speed, and these impulses themselves overcome 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 a signal, they redirect it to bipolar cells, and they redirect the signals already processed by themselves to ganglion cells, more than a million axons (neurites through which nerve impulses are transmitted) which make up a single optic nerve, through which data enters the brain.

Two layers of interneurons, before visual data is sent to the brain, contribute to the parallel processing of this information by six levels of perception located in the retina of the eye. This is necessary in order for the images to be 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, much is still unknown about the workings of the human brain, but even what the scientific world can provide today is 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?

And here's the thing: the retinal point of one eye exactly matches the retinal point of the other, and this means that both images, getting into the brain, can be superimposed on each other and combined together to form a single image. The information received by the photoreceptors of each of the eyes converges in the visual cortex of the brain, where a single image appears.

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

As you know, due to the refraction of light, the visual images entering the brain are initially very small and inverted, 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 images taken with both eyes are redirected to and the right parts are redirected to the left. Thus, each of the hemispheres of the looking 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 the connection.

Image separation and extremely complex optical paths 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, in the process of processing visual information, removes "blind" spots, distortions due to micro-movements of the eyes, blinking, angle of view, etc., offering its owner an adequate holistic image of the observed.

Another important element of the visual system is. It is impossible to belittle the importance of this issue, because. to be able to use the sight properly at all, we must be able to turn our eyes, raise them, lower them, in short, move our eyes.

In total, 6 external muscles can be distinguished that connect to the outer surface of the eyeball. These muscles include 4 straight (lower, upper, lateral and middle) and 2 oblique (lower and upper).

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 turning two eyes, the movement of all 12 muscles automatically changes (6 muscles for each eye). And it is remarkable that this process is continuous and very well coordinated.

According to the famous ophthalmologist Peter Jeni, the control and coordination of the connection 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 most complex processes occurring in the brain. If we add to this the accuracy of redirection of the gaze, the smoothness and evenness of movements, the speed with which the eye can rotate (and it totals up to 700 ° per second), and combine all this, we get a mobile eye that is actually phenomenal in terms of performance. system. And the fact that a person has two eyes makes it even more complicated - with synchronous eye movement, the same muscular innervation is required.

The muscles that rotate the eyes are different from the muscles of the skeleton, as they they are made up of many different fibers, and they are controlled by an even greater number of neurons, otherwise the accuracy 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.

Given that the eye is one of the most important organs of the human body, it needs continuous care. It is precisely for this that the “integrated cleaning system”, which consists of eyebrows, eyelids, eyelashes and lacrimal glands, is provided, if you can call it that.

With the help of the lacrimal glands, a sticky liquid is regularly produced, moving at a slow speed down the outer surface of the 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 excreted from the body.

Tears contain a very strong antibacterial substance that destroys viruses and bacteria. The eyelids perform the function of glass cleaners - they clean and moisturize the eyes due to involuntary blinking at an interval of 10-15 seconds. Together with the eyelids, eyelashes also work, preventing any litter, dirt, microbes, etc. from getting into the eye.

If the eyelids did not fulfill their function, a person's eyes would gradually dry up and become covered with scars. If there were no tear duct, the eyes would be constantly flooded with tear fluid. If a person did not blink, debris would get into his eyes, and he could even go blind. The entire "cleansing 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 in the process of his interaction with other people and the world around him. Eyes can radiate love, burn with anger, reflect joy, fear or anxiety, or fatigue. Eyes show where a person is looking, whether he is interested in something or not.

For example, when people roll their eyes while conversing with someone, this can be interpreted in a completely different way than the usual upward gaze. Big eyes in children cause delight and tenderness in others. And the state of the pupils reflects the state of consciousness in which a person is at a given moment in time. Eyes are an indicator of life and death, if we speak in a global sense. Perhaps for this reason they are called the "mirror" of the soul.

Instead of a conclusion

In this lesson, we examined 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 nevertheless we tried to convey the material so that you have a clear idea of ​​HOW a person sees.

You could not fail to notice that both the complexity and the possibilities of the eye allow this organ to surpass even the most modern technologies and scientific developments many times over. The eye is a clear demonstration of 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 over the years, vision may deteriorate, t .e. the visual system starts to fail.

But the deterioration of vision in most cases is not an irreversible process - knowing certain techniques, this process can be reversed, and vision can be made, 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 of our vision development course will be devoted to methods of restoring vision.

Look to 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. Only 1 option can be correct for each question. After you select one of the options, the system automatically moves on to the next question. The points you receive are affected by the correctness of your answers and the time spent on passing. Please note that the questions are different each time, and the options are shuffled.