Passage of light through the eye. Eye protection devices. Structure and functions of the layers of the retina. The structure and functions of the human visual organs. Eyeball and auxiliary apparatus Through what media of the eye does light pass?

The very front part of the eye is called the cornea. It is transparent (transmits light) and convex (refracts light).

Behind the cornea is Iris, in the center of which there is a hole - the pupil. The iris is made up of muscles that can change the size of the pupil and thus regulate the amount of light entering the eye. The iris contains the pigment melanin, which absorbs harmful ultraviolet rays. If there is a lot of melanin, then the eyes are brown, if the average amount is green, if there is little, they are blue.

The lens is located behind the pupil. This is a transparent capsule filled with liquid. Due to its own elasticity, the lens tends to become convex, while the eye focuses on close objects. When the ciliary muscle relaxes, the ligaments holding the lens tighten and it becomes flat, the eye focuses on distant objects. This property of the eye is called accommodation.

Located behind the lens vitreous, filling the eyeball from the inside. This is the third and final component of the refractive system of the eye (cornea - lens - vitreous).

Behind the vitreous body, on the inner surface of the eyeball is the retina. It consists of visual receptors - rods and cones. Under the influence of light, receptors are excited and transmit information to the brain. The rods are located mainly on the periphery of the retina, they provide only a black and white image, but they only need low lighting (they can work in the twilight). The visual pigment of the rods is rhodopsin, a derivative of vitamin A. The cones are concentrated in the center of the retina, they produce a color image and require bright light. There are two spots in the retina: the yellow spot (it has the highest concentration of cones, the place of greatest visual acuity) and the blind spot (it has no receptors at all, the optic nerve emerges from this place).

Behind the retina (the innermost layer of the eye) is located choroid(average). It contains blood vessels that supply the eye; in the front part it changes into iris and ciliary muscle.

Behind the choroid is located tunica albuginea, covering the outside of the eye. It performs a protective function; in the front part of the eye it is modified into the cornea.

Choose one, the most correct option. The function of the pupil in the human body is
1) focusing light rays onto the retina
2) regulation of luminous flux
3) transformation of light stimulation into nervous excitation
4) color perception

Answer

Choose one, the most correct option. A black pigment that absorbs light is located in the human organ of vision in
1) blind spot
2) choroid
3) tunica albuginea
4) vitreous body

Answer

Choose one, the most correct option. The energy of light rays entering the eye causes nervous excitement
1) in the lens
2) in the vitreous body
3) in visual receptors
4) in the optic nerve

Answer

Choose one, the most correct option. Behind the pupil in the human organ of vision is located
1) choroid
2) vitreous body
3) lens
4) retina

Answer

1. Establish the path of the light beam in the eyeball
1) pupil
2) vitreous body
3) retina
4) lens

Answer

2. Establish the sequence of passage of the light signal to the visual receptors. Write down the corresponding sequence of numbers.
1) pupil
2) lens
3) vitreous body
4) retina
5) cornea

Answer

3. Establish the sequence of arrangement of the structures of the eyeball, starting with the cornea. Write down the corresponding sequence of numbers.
1) retinal neurons
2) vitreous body
3) pupil in the pigment membrane
4) light-sensitive rod and cone cells
5) convex transparent part of the tunica albuginea

Answer

4. Establish the sequence of signals passing through the sensory visual system. Write down the corresponding sequence of numbers.
1) optic nerve
2) retina
3) vitreous body
4) lens
5) cornea
6) visual cortex

Answer

5. Establish the sequence of processes of passage of a ray of light through the organ of vision and a nerve impulse in the visual analyzer. Write down the corresponding sequence of numbers.
1) conversion of a ray of light into a nerve impulse in the retina
2) information analysis
3) refraction and focusing of a light beam by the lens
4) transmission of nerve impulses along the optic nerve
5) passage of light rays through the cornea

Answer

Choose one, the most correct option. The light-sensitive receptors of the eye - rods and cones - are located in the membrane
1) rainbow
2) protein
3) vascular
4) mesh

Answer

1. Choose the three correct options: light-refracting structures of the eye include:
1) cornea
2) pupil
3) lens
4) vitreous body
5) retina
6) yellow spot

Answer

2. Choose three correct answers out of six and write down the numbers under which they are indicated. The optical system of the eye consists of
1) lens
2) vitreous body
3) optic nerve
4) macula of the retina
5) cornea
6) tunica albuginea

Answer

1. Select three correctly labeled captions for the drawing “Structure of the eye.” Write down the numbers under which they are indicated.
1) cornea
2) vitreous body
3) iris
4) optic nerve
5) lens
6) retina

Answer

2. Select three correctly labeled captions for the drawing “Structure of the eye.” Write down the numbers under which they are indicated.
1) iris
2) cornea
3) vitreous body
4) lens
5) retina
6) optic nerve

Answer

3. Select three correctly labeled captions for the picture that depicts the internal structure of the organ of vision. Write down the numbers under which they are indicated.
1) pupil
2) retina
3) photoreceptors
4) lens
5) sclera
6) yellow spot

Answer

4. Select three correctly labeled captions for the picture that depicts the structure of the human eye. Write down the numbers under which they are indicated.
1) retina
2) blind spot
3) vitreous body
4) sclera
5) pupil
6) cornea

Answer

Establish a correspondence between visual receptors and their features: 1) cones, 2) rods. Write numbers 1 and 2 in the correct order.
A) perceive colors
B) active in good lighting
B) visual pigment rhodopsin
D) exercise black-and-white vision
D) contain the pigment iodopsin
E) distributed evenly across the retina

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. The differences between human daytime vision and twilight vision are that
1) cones work
2) color discrimination is not carried out
3) visual acuity is low
4) sticks work
5) color discrimination is carried out
6) visual acuity is high

Answer

Choose one, the most correct option. When viewing an object, a person’s eyes continuously move, providing
1) prevention of eye blindness
2) transmission of impulses along the optic nerve
3) the direction of light rays to the macula of the retina
4) perception of visual stimuli

Answer

Choose one, the most correct option. Human vision depends on the condition of the retina, since it contains light-sensitive cells in which
1) vitamin A is formed
2) visual images arise
3) black pigment absorbs light rays
4) nerve impulses are formed

Answer

Establish a correspondence between the characteristics and membranes of the eyeball: 1) albuginea, 2) vascular, 3) retina. Write numbers 1-3 in the order corresponding to the letters.
A) contains several layers of neurons
B) contains pigment in cells
B) contains the cornea
D) contains the iris
D) protects the eyeball from external influences
E) contains a blind spot

Answer

© D.V. Pozdnyakov, 2009-2019

The human eye is a remarkable achievement of evolution and an excellent optical instrument. The sensitivity threshold of the eye is close to the theoretical limit due to the quantum properties of light, in particular the diffraction of light. The range of intensities perceived by the eye is, the focus can move quickly from a very short distance to infinity.
The eye is a lens system that forms an inverted real image on a light-sensitive surface. The eyeball is approximately spherical in shape with a diameter of about 2.3 cm. Its outer shell is an almost fibrous opaque layer called sclera. Light enters the eye through the cornea, which is the transparent membrane on the outer surface of the eyeball. In the center of the cornea there is a colored ring - iris (iris) with pupil in the middle. They act like a diaphragm, regulating the amount of light entering the eye.
Lens is a lens consisting of a fibrous transparent material. Its shape and therefore focal length can be changed using ciliary muscles eyeball. The space between the cornea and the lens is filled with aqueous fluid and is called front camera. Behind the lens is a clear jelly-like substance called vitreous.
The inner surface of the eyeball is covered retina, which contains numerous nerve cells - visual receptors: rods and cones, which respond to visual stimulation by generating biopotentials. The most sensitive area of ​​the retina is yellow spot, which contains the largest number of visual receptors. The central part of the retina contains only densely packed cones. The eye rotates to examine the object being studied.

Rice. 1. Human eye

Refraction in the eye

The eye is the optical equivalent of a conventional photographic camera. It has a lens system, an aperture system (pupil) and a retina on which the image is captured.

The lens system of the eye is formed from four refractive media: the cornea, the aqueous chamber, the lens, and the glass body. Their refractive indices do not differ significantly. They are 1.38 for the cornea, 1.33 for the aqueous chamber, 1.40 for the lens and 1.34 for the vitreous (Fig. 2).

Rice. 2. The eye as a system of refractive media (numbers are refractive indices)

Light is refracted in these four refractive surfaces: 1) between the air and the anterior surface of the cornea; 2) between the posterior surface of the cornea and the water chamber; 3) between the water chamber and the anterior surface of the lens; 4) between the posterior surface of the lens and the vitreous body.
The strongest refraction occurs on the anterior surface of the cornea. The cornea has a small radius of curvature, and the refractive index of the cornea differs most from the refractive index of air.
The refractive power of the lens is less than that of the cornea. It accounts for about one-third of the total refractive power of the eye's lens systems. The reason for this difference is that the fluids surrounding the lens have refractive indices that are not significantly different from the refractive index of the lens. If the lens is removed from the eye, surrounded by air, it has a refractive index almost six times greater than in the eye.

The lens performs a very important function. Its curvature can be changed, which provides fine focusing on objects located at different distances from the eye.

Reduced eye

A reduced eye is a simplified model of a real eye. It schematically represents the optical system of a normal human eye. The reduced eye is represented by a single lens (one refractive medium). In a reduced eye, all the refractive surfaces of the real eye are summed algebraically to form a single refractive surface.
The reduced eye allows for simple calculations. The total refractive power of the media is almost 59 diopters when the lens is accommodated for vision of distant objects. The central point of the reduced eye lies 17 millimeters in front of the retina. A ray from any point on the object enters the reduced eye and passes through the central point without refraction. Just as a glass lens forms an image on a piece of paper, the lens system of the eye forms an image on the retina. This is a reduced, real, inverted image of an object. The brain forms the perception of an object in an upright position and in real size.

Accommodation

To see an object clearly, it is necessary that after the rays are refracted, an image is formed on the retina. Changing the refractive power of the eye to focus near and distant objects is called accommodation.
The farthest point to which the eye focuses is called farthest point visions - infinity. In this case, parallel rays entering the eye are focused onto the retina.
An object is visible in detail when it is placed as close to the eye as possible. Minimum clear vision distance – about 7 cm with normal vision. In this case, the accommodation apparatus is in the most tense state.
A point located at a distance of 25 cm, called dot best vision, since in this case all the details of the object in question are visible without maximum strain on the accommodation apparatus, as a result of which the eye may not get tired for a long time.
If the eye is focused on an object at a near point, it must adjust its focal length and increase its refractive power. This process occurs through changes in the shape of the lens. When an object is brought closer to the eye, the shape of the lens changes from a moderately convex lens shape to a convex lens shape.
The lens is formed by a fibrous jelly-like substance. It is surrounded by a strong flexible capsule and has special ligaments running from the edge of the lens to the outer surface of the eyeball. These ligaments are constantly tense. The shape of the lens changes ciliary muscle. The contraction of this muscle reduces the tension of the lens capsule, it becomes more convex and, due to the natural elasticity of the capsule, takes on a spherical shape. Conversely, when the ciliary muscle is completely relaxed, the refractive power of the lens is weakest. On the other hand, when the ciliary muscle is in its maximum contracted state, the refractive power of the lens becomes greatest. This process is controlled by the central nervous system.

Rice. 3. Accommodation in a normal eye

Presbyopia

The refractive power of the lens can increase from 20 diopters to 34 diopters in children. The average accommodation is 14 diopters. As a result, the total refractive power of the eye is almost 59 diopters when the eye is accommodated for distance vision, and 73 diopters at maximum accommodation.
As a person ages, the lens becomes thicker and less elastic. Consequently, the ability of a lens to change its shape decreases with age. The power of accommodation decreases from 14 diopters in a child to less than 2 diopters between the ages of 45 and 50 years and becomes 0 at the age of 70 years. Therefore, the lens almost does not accommodate. This disturbance of accommodation is called senile farsightedness. The eyes are always focused at a constant distance. They cannot accommodate both near and far vision. Therefore, to see clearly at various distances, an old person must wear bifocals with the upper segment focused for distance vision and the lower segment focused for near vision.

Refraction errors

Emmetropia . It is believed that the eye will be normal (emmetropic) if parallel light rays from distant objects are focused into the retina when the ciliary muscle is completely relaxed. Such an eye clearly sees distant objects when the ciliary muscle is relaxed, that is, without accommodation. When focusing objects at close distances, the ciliary muscle contracts in the eye, providing a suitable degree of accommodation.

Rice. 4. Refraction of parallel light rays in the human eye.

Hypermetropia (hyperopia). Hypermetropia is also known as farsightedness. It is caused either by the small size of the eyeball or by the weak refractive power of the eye's lens system. Under such conditions, parallel light rays are not refracted sufficiently by the lens system of the eye for the focus (and therefore the image) to be on the retina. To overcome this anomaly, the ciliary muscle must contract, increasing the optical power of the eye. Consequently, a farsighted person is able to focus distant objects on the retina using the mechanism of accommodation. There is not enough accommodation power to see closer objects.
With a small reserve of accommodation, a farsighted person is often unable to accommodate the eye sufficiently to focus not only close, but even distant objects.
To correct farsightedness, it is necessary to increase the refractive power of the eye. To do this, convex lenses are used, which add refractive power to the power of the eye's optical system.

Myopia . In myopia (or nearsightedness), parallel light rays from distant objects are focused in front of the retina, despite the fact that the ciliary muscle is completely relaxed. This happens due to the eyeball being too long, as well as due to the refractive power of the optical system of the eye being too high.
There is no mechanism by which the eye can reduce the refractive power of its lens less than is possible with complete relaxation of the ciliary muscle. The process of accommodation leads to deterioration of vision. Therefore, a person with myopia cannot focus distant objects on the retina. The image can only focus if the object is close enough to the eye. Therefore, a person with myopia has limited range of clear vision.
It is known that rays passing through a concave lens are refracted. If the refractive power of the eye is too great, as in myopia, it can sometimes be neutralized by a concave lens. Using laser technology, it is also possible to correct excessive corneal convexity.

Astigmatism . In an astigmatic eye, the refractive surface of the cornea is not spherical, but ellipsoidal. This occurs due to too much curvature of the cornea in one of its planes. As a result, light rays passing through the cornea in one plane are not refracted as much as rays passing through it in another plane. They do not gather in a common focus. Astigmatism cannot be compensated by the eye using accommodation, but it can be corrected using a cylindrical lens that will correct an error in one of the planes.

Correction of optical anomalies with contact lenses

Recently, plastic contact lenses have been used to correct various vision anomalies. They are placed against the front surface of the cornea and are secured by a thin layer of tears that fills the space between the contact lens and the cornea. Hard contact lenses are made of hard plastic. Their sizes are 1 mm in thickness and 1 cm in diameter. There are also soft contact lenses.
Contact lenses replace the cornea as the outer surface of the eye and almost completely cancel out the portion of the eye's refractive power that normally occurs on the front surface of the cornea. When using contact lenses, the anterior surface of the cornea does not play a significant role in the refraction of the eye. The front surface of the contact lens begins to play the main role. This is especially important in individuals with abnormally formed corneas.
Another feature of contact lenses is that, by rotating with the eye, they provide a wider area of ​​clear vision than regular glasses. They are also more convenient to use for artists, athletes, etc.

Visual acuity

The human eye's ability to see fine details clearly is limited. The normal eye can distinguish different point light sources located at a distance of 25 arc seconds. That is, when light rays from two separate points enter the eye at an angle of more than 25 seconds between them, they are visible as two points. Beams with smaller angular separation cannot be distinguished. This means that a person with normal visual acuity can distinguish two points of light at a distance of 10 meters if they are 2 millimeters apart.

Rice. 7. Maximum visual acuity for two point light sources.

The presence of this limit is provided for by the structure of the retina. The average diameter of the receptors in the retina is almost 1.5 micrometers. A person can normally distinguish two separate dots if the distance between them in the retina is 2 micrometers. Thus, in order to distinguish between two small objects, they must excite two different cones. At least there will be 1 unexcited cone between them.

Human perception of environmental objects occurs through projection onto. Light rays enter here, passing through a complex optical system.

Structure

Depending on the functions that the part of the eye performs, obaglaza.ru states, a distinction is made between the light-conducting and light-receiving parts.

Light-conducting section

The light-conducting department includes the organs of vision with a transparent structure:

• front moisture;

Their main function, according to obaglaza.ru, is to transmit light and refract rays for projection onto the retina.

Light-receiving department

The light-receiving part of the eye is represented by the retina. Following a complex path of refraction in the cornea and lens, the light rays are focused at the back in an inverted manner. In the retina, due to the presence of receptors, a primary analysis of visible objects occurs (differences in colors, light intensity).

Ray Transformation

Refraction is the process of light passing through the optical system of the eye, recalls obaglaza ru. The concept is based on the principles of the laws of optics. Optical science substantiates the laws of the passage of light rays through various media.

1. Optical axes

• Central - a straight line (the main optical axis of the eye) passing through the center of all refractive optical surfaces.
• Visual - rays of light that fall parallel to the main axis are refracted and localized at the central focus.

2. Focus

The main front focus is the point of the optical system where, after refraction, the light fluxes of the central and visual axis are localized and form an image of distant objects.

Additional focuses - collects rays from objects placed at a finite distance. They are located further than the main front focus, since in order for the rays to focus, a larger refraction angle is needed.

Research methods

To measure the functionality of the optical system of the eyes, first of all, according to the site, it is necessary to determine the radius of curvature of all structural refractive surfaces (the front and back sides of the lens and cornea). Quite important indicators are also the depth of the anterior chamber, the thickness of the cornea and lens, the length and angle of refraction of the visual axes.

All these quantities and indicators (except refraction) can be determined using:

• Ultrasound examination;
• Optical methods;
• X-ray.

Correction

Measuring the length of the axes is widely used in the field of the optical system of the eyes (microsurgery, laser correction). With the help of modern medical advances, obaglaza.ru suggests, it is possible to eliminate a number of congenital and acquired pathologies of the optical system (lens implantation, manipulation of the cornea and its prosthetics, etc.).

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 an even greater number of 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 Higher Power is responsible for the creation of man, then you can attribute this credit 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 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 it contains inhibits the development of blood vessels - a process that occurs in almost every tissue of the 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 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 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 different types of 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 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 complex structure of the 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"

Focusing results in focusing the image on the retina, which is a multi-layered light-sensitive tissue 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 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. 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 sensitive to light, but are able to distinguish colors - optimal operation of the 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 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, there is still a lot that is 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?

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 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 important element of 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 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 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 controlled by an even larger 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.

Considering that the eye is one of the most important organs of the human body, it 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 that moves slowly 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 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 there were no tear ducts, 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 in children evoke delight and tenderness among those around them. 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. 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 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 vision can deteriorate over the years, i.e. .e. the visual system begins to malfunction.

But 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 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 moves on to the 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.

Equipment: collapsible model of the eye, “Visual Analyzer” table, three-dimensional objects, reproductions of paintings. Handouts for desks: drawings “Structure of the eye”, cards for reinforcement on this topic.

During the classes

I. Organizational moment

II. Testing students' knowledge

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

2. Additional information on homework (student messages):

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

III. learning new material

(Communication of the topic of the lesson, goals, objectives and motivation for students’ educational 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 know the world around us primarily through vision. This is how we get an idea of ​​the shape, size of an object, its color, notice danger in time, and admire the beauty of nature.

Thanks to vision, the blue sky, young spring foliage, bright colors of flowers and butterflies fluttering above them, and golden fields open before us. 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 on from generation to generation through books, paintings, sculptures, architectural monuments, which we perceive with the help of sight.

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

2. Eye position

Look at the picture in the textbook and determine which bone processes are involved in the formation of the orbit. ( Frontal, zygomatic, maxillary.)

What is the role of the eye sockets?

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 and down, right and left, and describes a circle with it.

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

3. Eye protection

Experiment No. 2. Observe the blinking of your neighbor’s eyelids and answer the question: what function do the eyelids perform? ( Protection from light irritation, eye protection from foreign particles.)

Eyebrows catch sweat flowing from the forehead.

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

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4. Structure of the visual analyzer

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

ray of light → 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 explained by a person’s life experience, as well as the interaction of signals coming from all 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 cerebrum).

The eye is a self-adjusting device; it allows you to see near and distant objects. Helmholtz also believed that the model of the eye is a camera, the lens is the transparent refractive medium 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 part of the visual fields from both eyes is transmitted to the right hemisphere, and from the right part of the visual fields of both eyes - to the left.

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

Table. 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 inverse 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. Match.

1. Lens. 2. Retina. 3. Receptor. 4. Pupil. 5. Vitreous body. 6. Optic nerve. 7. Tunica albuginea and cornea. 8. Light. 9. Choroid. 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.
D. Changes curvature.
D. Provides various visual stimulations.
E. Protective membranes of the eye.
G. Place of exit of the optic nerve.
H. Place of image formation.
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; F –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 receptors are excited in a certain combination, and we perceive the image when the nerve impulses reach the cerebral cortex.)

The eyes feel neither heat nor cold. Why? ( The cornea has no receptors for heat and cold.)

Two students argued: one argued that the eyes get more tired when looking at small objects located close, and the other - at distant objects. Which one is right? ( The eyes become more tired when looking at objects located close to them, since this causes the muscles that ensure the functioning (increased curvature) of the lens to become very tense. Looking at distant objects is a rest for the eyes.)

Task 3. Label the elements of the eye structure indicated by numbers.

Literature

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

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