Anatomical questions have always been of some interest. After all, they concern each of us directly. Almost everyone at least once, but was interested in what the eye consists of. After all, it is the most sensitive sense organ. It is through the eyes, visually, that we receive about 90% of the information! Only 9% - with the help of hearing. And 1% - through other organs. Well, the structure of the eye is a really interesting topic, so it's worth considering it in as much detail as possible.
Shells
Start with terminology. The human eye is a paired sensory organ that perceives electromagnetic radiation in the light wavelength range.
It consists of shells that surround the inner core of the organ. Which, in turn, includes the aqueous humor, the lens and the vitreous body. But more on that later.
Telling about what the eye consists of, special attention should be paid to its shells. There are three of them. The first is external. Dense, fibrous, external muscles of the eyeball are attached to it. This shell performs a protective function. And it is she who determines the shape of the eye. Consists of the cornea and sclera.
The middle shell is also calledvascular. It is responsible for metabolic processes, provides nutrition to the eyes. Consists of the iris, ciliary body and choroid. In the very center is the pupil.
And the inner shell is often called mesh. The receptor part of the eye, in which light is perceived and information is transmitted to the central nervous system. In general, this can be said in short. But, since each component of this body is extremely important, it is necessary to separately touch upon each of them. This will help you better understand what the eye is made of.
Cornea
So, this is the most convex part of the eyeball, which makes up its outer shell, as well as a light-refracting transparent medium. The cornea looks like a convex-concave lens.
Its main component is the connective tissue stroma. Anteriorly, the cornea is covered with stratified epithelium. However, scientific words are not very easy to understand, so it is better to explain the topic in a popular way. The main properties of the cornea are sphericity, specularity, transparency, increased sensitivity and the absence of blood vessels.
All of the above determines the "appointment" of this part of the organ. In fact, the cornea of the eye is the same as the lens of a digital camera. Even in structure, they are similar, because both one and the other is a lens that collects and focuses light rays in the required direction. This is the function of the refractive medium.
Talking about what the eye consists of, one cannot help but touch upon the negativeimpact he has to deal with. The cornea, for example, is most susceptible to external stimuli. To be more precise - the impact of dust, changes in lighting, wind, dirt. As soon as something in the external environment changes, the eyelids close (blinking), photophobia, and tears begin to flow. Thus, it can be said that damage protection is activated.
Protection
A few words should be said about tears. It is a natural biological fluid. It is produced by the lacrimal gland. A characteristic feature is a slight opalescence. This is an optical phenomenon, due to which the light begins to scatter more intensely, which affects the quality of vision and the perception of the surrounding image. Tears are 99% water. One percent is inorganic substances, which are magnesium carbonate, sodium chloride, and also calcium phosphate.
Tears have bactericidal properties. They wash the eyeball. And its surface thus remains protected from the effects of dust particles, foreign bodies and wind.
Another component of the eye is eyelashes. On the upper eyelid, their number is approximately 150-250. On the bottom - 50-150. And the main function of eyelashes is the same as that of tears - protective. They prevent dirt, sand, dust, and in the case of animals, even small insects from entering the surface of the eye.
Iris
So, above it was told about what the outer shell of the eye consists of. Now we can talk about the average. Naturally, we will talk aboutiris. It is a thin and movable diaphragm. It is located behind the cornea and between the chambers of the eye - right in front of the lens. Interestingly, it practically does not transmit light.
The iris consists of pigments that determine its color, and circular muscles (due to them, the pupil narrows). By the way, this part of the eye also includes layers. There are only two of them - mesodermal and ectodermal. The first is responsible for the color of the eye, as it contains melanin. The second layer contains pigment cells with fuscin.
If a person has blue eyes, then his ectodermal layer is loose and contains little melanin. This shade is the result of light scattering in the stroma. By the way, the lower its density, the more saturated the color is.
People with a mutation in the HERC2 gene have blue eyes. They produce a minimum of melanin. The density of the stroma in this case is higher than in the previous case.
Green eyes have the most melanin. By the way, the red hair gene plays an important role in the formation of this shade. Pure green is very rare. But if there is at least a "hint" of this shade, then they are called as such.
But still, most of the melanin is found in brown eyes. They absorb all the light. Both high and low frequencies. And the reflected light gives a brown tint. By the way, initially, many thousands of years ago, all people were brown-eyed.
There is also a black color. Eyes of this shade contain so much melanin that all the light entering them is completely absorbed. And, by the way, often such a “composition”causes a grayish tint to the eyeball.
Choroid
It should also be noted with attention, telling what the human eye consists of. It is located directly under the sclera (protein membrane). Its main property is accommodation. That is, the ability to adapt to dynamically changing external conditions. In this case, it concerns the change in refractive power. A simple illustrative example of accommodation: if we need to read what is written on the package in small print, we can look closely and distinguish the words. Need to see something far away? We can do it too. This ability is our ability to clearly perceive objects located at a certain distance.
Naturally, when talking about what the human eye consists of, one cannot forget about the pupil. This is also a rather "dynamic" part of it. The pupil diameter is not fixed, but constantly narrowing and expanding. This is due to the fact that the amount of light that enters the eye is regulated. The pupil, changing in size, "cuts off" too bright sunlight on a particularly clear day, and misses their maximum amount in foggy weather or at night.
Must know
It is worth focusing on such an amazing component of the eye as the pupil. This is perhaps the most unusual in the topic under discussion. Why? If only because the answer to the question of what the pupil of the eye consists of is such - from nothing. In fact, it is! After all, the pupil is a hole in the tissues of the eyeball. But next towith him are the muscles that allow him to perform the above named function. That is, adjust the flow of light.
The unique muscle is the sphincter. It surrounds the extreme part of the iris. The sphincter consists of interwoven fibers. There is also a dilator - the muscle that is responsible for dilating the pupil. It consists of epithelial cells.
One more interesting fact is worth noting. The middle shell of the eye consists of several elements, but the pupil is the most fragile. According to medical statistics, 20% of the population has a pathology called anisocoria. It is a condition in which pupil sizes differ. They can also be deformed. But not all of these 20% have a pronounced symptom. Most do not even know about the presence of anisocoria. Many people become aware of it only after visiting a doctor, which people decide to do, feeling foggy, pain, ptosis (drooping of the upper eyelid), etc. But some people have diplopia - “double pupil”.
Retina
This is the part that needs special attention when talking about what the human eye is made of. The retina is a thin membrane, closely adjacent to the vitreous body. Which, in turn, is what fills 2/3 of the eyeball. The vitreous body gives the eye a regular and unchanging shape. It also refracts light entering the retina.
As already mentioned, the eye consists of three shells. But this is just the foundation. After all, it consists of 10 more layersretina! And to be more precise, its visual part. There is also a “blind” one, in which there are no photoreceptors. This part is divided into ciliary and rainbow. But it's worth going back to ten layers. The first five are: pigmentary, photosensory and three external (membrane, granular and plexus). The rest of the layers are similar in name. These are three internal ones (also granular, plexus-like and membranous), as well as two more, one of which consists of nerve fibers, and the other of ganglion cells.
But what exactly is responsible for visual acuity? The parts that make up the eye are interesting, but I want to know the most important thing. So, the central fovea of the retina is responsible for visual acuity. It is also called the "yellow spot". It has an oval shape, and is opposite the pupil.
Photoreceptors
An interesting sense organ is our eye. What it consists of - the photo is provided above. But nothing has been said about photoreceptors yet. And, to be more precise, about the rods and cones located on the retina. But this is also an important component.
It is they who contribute to the transformation of light irritation into information that enters the central nervous system through the fibers of the optic nerve.
Cones are highly sensitive to light. And all because of the content of iodopsin in them. It is the pigment that provides color vision. There is also rhodopsin, but this is the complete opposite of iodopsin. Since this pigment is responsible for twilight vision.
A person with good 100% vision has approximately 6-7 million cones. Interesting that they are differentless sensitivity to light (they have it about 100 times worse) than sticks. However, fast movements are better perceived. By the way, there are more sticks - about 120 million. They just contain the notorious rhodopsin.
It is the sticks that provide the visual ability of a person in the dark. Cones are not active at all at night - because they need at least a minimal flow of photons (radiation) to work.
Muscles
They also need to be told, discussing the parts that make up the eye. The muscles are what keeps the apples in the eye socket straight. All of them originate from the notorious dense connective tissue ring. The major muscles are called obliques because they attach to the eyeball at an angle.
The topic is best explained in simple terms. Each movement of the eyeball depends on how the muscles are fixed. We can look to the left without turning our heads. This is due to the fact that the direct motor muscles coincide in their location with the horizontal plane of our eyeball. By the way, they, together with oblique ones, provide circular turns. Which includes every gymnastics for the eyes. Why? Because when performing this exercise, all the eye muscles are involved. And everyone knows that in order for this or that training (no matter what it is connected with) to give a good effect, every component of the body needs to work.
But that's not all, of course. There are also longitudinal muscles that begin to work at the momentwhen we look into the distance. Often, people whose activities are associated with painstaking or computer work feel pain in their eyes. And it becomes easier if they are massaged, closed, rotated. What causes pain? Due to muscle strain. Some of them work constantly, while others rest. That is, for the same reason that hands can hurt if a person was carrying some kind of heavy thing.
Crystal
Telling about what parts the eye consists of, one cannot help but touch upon this “element”. The lens, which has already been mentioned above, is a transparent body. It is a biological lens, to put it simply. And, accordingly, the most important component of the light-refracting eye apparatus. By the way, the lens even looks like a lens - it is biconvex, round and elastic.
He has a very fragile build. Outside, the lens is covered with the thinnest capsule that protects it from external factors. Its thickness is only 0.008mm.
The lens is susceptible to various diseases. The worst is the cataract. With this disease (age-related, as a rule), a person sees the world dimly, blurry. And in such cases, it is necessary to replace the lens with a new, artificial one. Fortunately, it is located in our eye in such a place that it can be changed without touching the rest of the parts.
In general, as you can see, the structure of our main sense organ is very complex. The eye is small, but it includes just a huge number of elements (remember, at least 120million sticks). And it would be possible to talk about its components for a long time, but I managed to list the most basic ones.
