The structure of the eye and its work
Mar 29, 2018
The eye is located in the orbital cavity of the skull. From the bones of the orbital cavity to the outer surface of the globular eyeball, the muscles that turn it are suitable. In the future, we will specifically focus on the work of these muscles, since, as will be shown, they have the most direct relation to the power of our vision.
The organs surrounding the eye are intended by Nature to protect it from the harmful effects of the external environment. Hairs of the eyebrows lead to the sides flowing from the forehead liquid( most often sweat drops), eyelashes prevent the ingress of dust into the eye. The lacrimal gland located at the outer corner of the eye also belongs to its protective organs. It emits a tear, which all the time wets the surface of the eyeball, does not allow drying out the living cells of the outer layer of the eye, warms it, removes foreign particles that come into its eyes, and then drains from the inner corner of the eye through the tear duct to the nasal cavity.
How does the eye work? The dense white skin( sclera), covering the eye from the outside, protects it from mechanical and chemical damage, from the penetration of foreign particles and microorganisms. In the front of the eye, this sheath passes
into a transparent cornea, the , which, like a glazed window, freely passes light rays. The average - choroid is permeated with a dense network of blood vessels that supply the eyeball with blood. On the inner surface of this shell is a thin layer of coloring matter - black pigment, which absorbs light rays. In the front of the eye, opposite the cornea, the vascular membrane passes into the iridescent, which can have a different color - from light blue to black. It is determined by the amount and composition of the pigment contained in this coating. The cornea and iris do not adhere to each other tightly. Between them is a space filled with perfectly clear liquid.
Cornea and clear liquid pass light rays that enter the eyeball through the pupil - a hole located in the middle of the iris. It is necessary to get inside the eye the rays of bright light, as there is a reflex narrowing of the pupil hole. With a weak light, the pupil, on the contrary, expands. Directly behind the pupil is the transparent lens, the having the shape of a biconvex lens and surrounded by the ring, or, in a different way, the ciliary muscle. According to Western science, the ability of the ring muscle to reduce
and relaxation, on the one hand, and the natural elasticity of the lens, on the other, are the main conditions for focusing in the eye. We will return to this issue in the future, here, in passing, we note that we share this conviction of our Western colleagues only in part.
Passing through the crystalline lens and then through a transparent, crystal-like crystal, vitreous body, which fills the entire inner part of the eyeball, rays of light fall on the inner, very thin shell of the eye - the retina. Retin-A, despite the fact that it is extremely thin( in fact its thickness varies from 1/33 cm to less than half of this value), it has an extremely complex structure. It consists of eight layers, of which, it is believed, only one is associated with the perception of visual images. This layer consists of the smallest rod-shaped and cone-shaped cells, differing from each other in shape and very unevenly distributed across the retina. These light-sensing cells are called visual receptors. In them, under the influence of stimulation caused by light rays, there is an excitation that is performed on the processes of neurons, collecting in the optic nerve. On it the excitement is already in the brain.
The visual receptors located in the retina divide, as we have said, into two groups different in structure and function - the so-called rods and cones. The rods are irritated by weak twilight light, but do not have the ability to perceive color. The cones are irritated only by bright light and are capable of perceiving colors. The excitations arising in the receptors are transmitted along the centripetal neurons, the processes of which in a certain region of the retina are assembled, as we have said, in the optic nerve. It passes through all the shells of the eyeball, comes out of it and is sent to the brain. In the place where the optic nerve emerges from the retina, there are no light-sensing cells in it. Images of objects arising on this site are not perceived by us. Therefore, he received the name blind spot.
In the middle of the retina, just in front of the pupil, there is a small round elevation - the so-called yellow spot, representing congestion of cones. That is why we see most clearly those objects that are directly opposite the pupil. In the center of this spot is placed fovea - a deep fovea of a darker color. In the center of the fossa there is not a single stick, but the cones are elongated and closely pressed together. Other layers in this place, on the contrary, are extremely thin or disappear altogether. Outside the center of the fovea, the cones become thicker and less common, alternating with chopsticks, whose numbers are increasing as they move toward the edges of the retina.
The ability of a yellow spot to give the brain detailed information about the subject under consideration is associated with a very high concentration of light-sensing elements here, and also with the fact that each cone is connected to its own individual neuron. The rods of such an individual neuron do not have and are forced to be grouped together by whole clusters around a single cell.
The cones are not only in the yellow spot, but in the rest of the central part of the visual field, only here their concentration is much lower. And on the periphery of cones is not at all. There are only sticks - light-sensing elements of higher sensitivity. Since several sticks send their information to the same nerve cell, at twilight very weakly excited sticks can energize their neuron by joint efforts and the eye will still see something, whereas the cones that are addressed only to their own nerve cell, in this case are powerless. It is the insignificant involvement of the cones in the twilight light that explains the phenomenon that for the human eye at night all cats are sulfur.
Thus, we use the rods only at dusk, when the cones are simply a hindrance. We could see much better at night if it were not for the habit of focusing the image on the yellow spot - the so-called central fixation. Therefore, at night, we see things much better, the image of which appears on the side parts of the retina, and this happens when we do not look directly at the object that we want to see. Incidentally, for the development of this skill is exercise number 3 V group( § 20).
As for a night view, a significant part of the retina is completely or partially useless - the one that is so familiar and convenient to use during the day, you only need to train peripheral areas in the twilight light, that is, those that bring us little benefit in the daytime.
Let's go, however, further. Receptors of the eye perceive visual irritations due to the fact that images appear on the retina of objects visible to us. How does this happen? The rays from the objects to which our eyes are directed pass through the cornea, the fluid between it and the iris, the lens and the vitreous. In each of these environments, they change their direction - they are refracted. This process of refraction of light rays in the optical system of the eye is called refraction. But it would be more accurate to understand the refractive power of the of the eye optical system under the refraction of the .
And then we finally came to a rather delicate issue, in which our views are at variance with the views of orthodox Western science. This question is how the accommodation process, the , ie the eye's adaptation to the vision at a distance occurs. However, we must warn the reader in advance that we are not going to insult here the best feelings of our Western scientific colleagues, or to conduct with them any in-depth controversy on the issues of the affected area. We simply point out what is happening, and we completely leave the care of our understanding of the truth in the hands of our Western friends.
When considering close subjects, a clear image of them can appear on the retina only if the refraction of the rays in the eye is greater than when examining distant objects. And most ophthalmologists believe that the main thing for the refraction of light in the eye is the lens. They believe that we can see clearly both objects that are at a relatively great distance from us, and objects that are close to us, only because the biconvex lens due to the surrounding annular muscle can change its curvature, become more convex ormore flat. When the annular muscle contracts the lens, then, in their opinion, it should increase its curvature;and as soon as the muscle relaxes, the lens, due to natural elasticity, again flattened.
When examining objects close to the eye, the annular muscle tenses, and the curvature of the lens increases, so that the refraction of the rays in the eye becomes large, and a clear image of the subject under consideration appears on the retina.
When we peer into distant objects, the muscles relax, and the lens is flattened, so that the refraction of the rays in it becomes smaller. That is why in normal vision on the retina of the eye, in all cases, a clear image of the objects should be obtained.
This is a general outline of the view of orthodox ophthalmology. We dwelled on it in detail because, at least in part, but it is fair, and,
, to go further, we needed to master this relatively simple point of view.
However, in reality everything is much more complicated. I must say that in Western science there is now a fairly influential direction, close in many of its views to the point of view of the yogis, which has a completely different opinion on this score.
This school believes that the decisive factor of refraction in the eye are the surrounding eyeball straight and oblique muscles. In the opinion of this school, the role of straight and oblique muscles is not limited to only that, cutting, they turn the eyeball, allowing us to thereby change the direction of view and consider those or other of the objects around us.
The task of these muscles is primarily to change the shape of the eyeball, which as necessary becomes that elongated, then flattened in the anteroposterior axis, , which allows you to achieve a clear image of objects on the retina according to the distance they are removed from our eyes.
With this understanding, the opinion of official Western ophthalmology, which considers that the shape of the eyeball is unchanged, proves to be untenable. It is this opinion that gave rise to a theory that attempts to explain the abnormalities of refraction by the congenital irregularity of the shape of the eyeball. Thus, this theory attributes the merit in the accommodation exclusively to the operation of the annular muscle and the change in the curvature of the lens. At the same time, the congenital elongation of the eyeball should be the cause of myopia, and the shortening - , respectively, of hypermetropia. However, since the shape of the eyeball changes as and when necessary, this theory just as well as the opinion giving rise to it is not worthy of attention.
It is well known that after the removal of the lens due to cataracts, the eye is often able to be accommodated in the same way as before. In itself, this fact ruthlessly crosses out the refractional theory of the orthodox. Dr. William Bates writes on this subject that he observed many such cases. Patients do not have
only read the font diamonds in their glasses for distance at a distance of 33, 26 and less centimeters( the hardest time in such cases is to read at very small distances), but one patient could do it without glasses at all. At the same time, as Dr. Bates points out, the retinoscope in all cases showed that a real accommodation is taking place and that it is not carried out in any intricate way that dogmatists try to explain this inconvenient phenomenon, but by accurately adjusting the focus to the appropriate distances. Therefore, it is quite appropriate to talk about the strength of the straight and oblique muscles of the eye, on the one hand, and the natural elasticity of the eyeball, on the other.
Summing up our essay on the refraction of light rays in the eye, we will say that we do not share the categorical nature of any of the opposing sides in the West, since such categoricality would rule out the correctness of the opposite point of view. In our opinion, each of these two theories is valid, and they should not be opposed, but viewed in unity. However, if the activity of the straight and oblique muscles is to be recognized as determining in the refractive force of the eye, then behind the lens and the ring muscle, it is necessary to leave only the auxiliary function of the subcorrection. This approach, I think, will explain all the contradictions and inconsistencies of Western theories prone to excessive exclusivity and rivalry. It is not necessary to think that Nature, this greatest and most perfect constructor, creates unnecessary details in their machines or will tolerate their presence if they are so.
In the future, we will, as necessary, more than once will return to this point, and now again turn to the image that is obtained on the retina. Since the lens is a biconvex lens, the image of objects arising on the retina, in accordance with the laws of physics, is reduced and inverted. The complex process of perception of visual stimuli, begun in the retina, ends in the visual zone of the cortex of the cerebral hemispheres. It is carried out thanks to the visual analyzer, which conducts the final discrimination of stimuli. That is why we distinguish the shape of objects, their color, size, illumination, location, movement. The image of objects on the retina, inverted by the lens, in the brain once again turns up to coincidence with their real location. This is due to the influence of various psychic causes, among which the determining role is played by the interaction of excitations entering the brain from all sense organs.
The eye, therefore, is simply a light-receiving device, like a camera or a movie camera, only our brain "sees".This he adds the information obtained from millions of photosensitive cells of our eye, into intricate pictures;it is here, in the brain, "the pictures" that are made by the eyes appear. It is because he sees not the eye and hears not the ear, but the brain that mediates our soul, our personal "I" in the crude world of matter, is explained by the curious circumstance that we so often see or hear not what is but onlysomething that we already know or know. How many times each of us caught himself on that did not notice any features of the subject, dozens of times before we saw it, while someone else who knew did not tell us about it!