Anatomical issues have always been of particular interest. After all, they concern each of us directly. Almost all, at least once, were interested in what the eye consists of. After all, this is the most sensitive sense organ. It is through the eyes, visually, that we receive about 90% of the information! Only 9% through hearing. And 1% - through other organs. Well, the structure of the eye is a really interesting topic, so you should consider it in as much detail as possible.
Shell
Start with terminology. The human eye is a paired sensory organ that perceives electromagnetic radiation in the light wavelength range.
It consists of shells surrounding the inner core of an organ. Which, in turn, includes aqueous humor, the lens and the vitreous. But more on that later.
Talking about what the eye consists of, special attention should be paid to its shells. There are three of them. The first is outdoor. Dense, fibrous, the 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 cornea and sclera.
The middle membrane is also called vascular. She is responsible for metabolic processes, provides nutrition to the eyes. Consists of the iris, ciliary body and choroid. In the center is the pupil.
And the inner shell is often called mesh. The receptor part of the eye, in which light is perceived and transmitted to the central nervous system. In general, this can be briefly described. But, since each component of this body is extremely important, it is necessary to separately pay attention to each of them. So it’s better to learn what the eye consists of.
Cornea
So, this is the most convex part of the eyeball, 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. In front, the cornea is covered with stratified epithelium. However, scientific words are not very simple in terms of perception, 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 "purpose" of this part of the body. 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 necessary direction. This is the function of the refractive medium.
Talking about what the eye consists of, one cannot help but touch upon the negative influences with which he has to cope. The cornea, for example, is most susceptible to external stimuli. To be more precise - the effects of dust, changes in lighting, wind, and dirt. As soon as something in the external environment changes, the eyelids close (blink), photophobia closes, and tears begin to flow. So, it can be said, damage protection is activated.
Protection
A few words worth saying 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 light begins to scatter more intensively, which affects the quality of vision and perception of the surrounding image. The tear fluid is 99% water. One percent is inorganic substances, which are magnesium carbonate, sodium chloride, and also calcium phosphate.
Tears have bactericidal properties. It is they who wash the eyeball. And its surface, thus, remains protected from dust, foreign bodies and wind.
Another component of the eye is eyelashes. On the upper eyelid, their number is approximately 150-250. At 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 getting onto the surface of the eye.
Iris
So, above it was told about what the outer shell of the eye consists of. Now you can talk about the average. Naturally, we will talk about the iris. It is a thin and movable diaphragm. It is located behind the cornea and between the cameras of the eye - right in front of the lens. Interestingly, it practically does not let in 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 - mesoderm and ectoderm. The first is responsible for the color of the eye, since it contains melanin. In the second layer are pigment cells with fuscin.
If a person has blue eyes, then his ectoderm 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.
Blue eyes have people with a mutation in the HERC2 gene. They produce a minimum of melanin. The stroma density in this case is higher than in the previous case.
In the green eyes, melanin is most. By the way, the gene of red hair 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 such.
But still, most of all melanin is contained 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 still black. Eyes of such a shade contain so much melanin that all the light that enters them is absorbed entirely. And, by the way, often such a “composition” causes a grayish tint of the eyeball.
Vascular membrane
It also needs to be noted with attention, telling what a human eye consists of. It is located directly under the sclera (protein coat). Its main property is accommodation. That is, the ability to adapt to dynamically changing external conditions. In this case, this refers to a change in refractive power. A simple visual example of accommodation: if we need to read what is written on the packaging in small print, we can take a closer look and distinguish between words. Need to see something in the distance? We can do it too. This ability lies in our ability to clearly perceive objects located at one or another distance.
Naturally, talking about what the human eye consists of, you can not forget about the pupil. This is also a rather “dynamic" part of it. The pupil diameter is not fixed, but constantly tapering and expanding. This is due to the fact that the flow of light that goes into the eye is regulated. The pupil, changing in size, "cuts off" too bright sun rays on a particularly clear day, and passes their maximum number in foggy weather or dark.
Should know
On such an amazing component of the eye as the pupil, it is worth focusing attention. 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 a thing - of nothing. In fact, it is! After all, the pupil is a hole in the tissues of the eyeball. But next to him are the muscles that allow him to perform the above function. That is, regulate 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 the expansion of the pupil. It consists of epithelial cells.
It is worth noting the attention of another interesting fact. The middle shell of the eye consists of several elements, but the pupil is the most fragile. If you believe the medical statistics, then 20% of the population has a pathology called anisocoria. It is a condition in which the size of the pupils 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, to which people decide, feeling foggy, pain, ptosis (drooping of the upper eyelid) , etc. But some have diplopia - a “double pupil”.
Retina
This is the part that should be noted with special attention, talking about what the human eye consists of. The retina is a thin shell adjacent to the vitreous. 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, another 10 layers consists of the retina! And to be more precise, its visual part. There is also a "blind" in which there are no photoreceptors. This part is divided into ciliary and iridescent. But it is worth returning to ten layers. The first five are: pigment, photosensory and three external (membrane, granular and plexus). The remaining layers are similar in name. These are three internal (also granular, plexiform and membrane), 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 retinal fossa 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 yet been said about photoreceptors. And, to be more precise, about sticks and cones located on the retina. But this is also an important component.
They 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. This 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 percent vision has approximately 6-7 million cones. Interestingly, they are less sensitive to light (they have it about 100 times worse) than sticks. However, they perceive fast movements better. Incidentally, there are more rods - approximately 120 million. They just contain the notorious rhodopsin.
It is the sticks that provide the visual ability of a person in the dark. The cones are not active at night at all - because they need at least a minimal flux of photons (radiation) to work.
Muscle
It is also necessary to tell about them, discussing the parts of which the eye consists. Muscles - this is what provides a direct arrangement of apples in the orbit. All of them originate from the notorious connective tissue tight ring. The main muscles are called oblique because they are attached to the eyeball at an angle.
The topic is best explained in plain language. 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 rectus motor muscles coincide in their location with the horizontal plane of our eyeball. By the way, they also, in conjunction with oblique, 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: for this or that training (no matter what it is connected with) to give a good effect, each component of the body needs to work.
But that, of course, is not all. There are also longitudinal muscles that begin to work at the moment when we look into the distance. Often people whose activities are associated with painstaking or computer work, feel pain in the eyes. And it becomes easier if you massage them, squeeze them, rotate them. What causes pain? Due to muscle strain. Some of them work constantly, while others rest. That is, for the same reason that hands may hurt if a person carried some heavy thing.
Lens
Talking about what parts the eye consists of, one cannot help but pay attention to this “element”. The lens, which was already mentioned above, is a transparent body. This is a biological lens, in simple terms. 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.
It has a very fragile structure. Outside, the lens is covered with the thinnest capsule that protects it from external factors. Its thickness is only 0.008 mm.
The lens is susceptible to various diseases. The most difficult is cataract. With this disease (age-related, as a rule), a person sees the world muddy, blurry. And in such cases, the lens needs to be replaced with a new, artificial one. Fortunately, it is in our eye in such a place that it is possible to change it 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 includes just a huge number of elements (remember, at least 120 million sticks). And it would be possible to talk about its components for a long time, but we managed to list the most basic ones.