The eyes are the organ responsible for the sense of sight. Due to the fact that we have two eyes, our brain is able to create spatial images and can also judge distance. The eyes continually provide the brain with signals that define our surroundings. Interestingly, almost 90 percent of all received stimuli come to us through the organ of vision.
The human eye is made of many elements and is a very complex organ of our body. To be able to see clearly, many complex processes take place in the eye and in the brain. Thanks to the structure of our eye, we can receive visual signals in various lighting conditions. We are also able to distinguish the colors that surround us.
The anatomy of the eye is difficult to assimilate. The description of the structure of the eye should begin with the eyeball. It resembles a sphere in shape and is placed in an eye socket to protect it. The eyeball is filled with a vitreous body, which is roughly 98 percent water and the rest is hyaluronic acid and collagen fibers. The vitreous body is part of the optical system. Thanks to it, light rays can move from the lens of the eye to the retina. It is also worth mentioning that the inside of the eyeball consists of several membranes.
Starting from the outside, we can distinguish: sclera, choroid and retina. The first membrane, or the sclera, is a white sheath that protects it. The sclera sings the eye from the back of the optic nerve to the front cornea. The stability of the sclera is related to the fibrous collagen it consists of. Interestingly, the sclera does not have the same thickness all over its surface. The part at the back of the eye is thicker and the part at the front is thinner.
Additionally, the sclera has two “holes”. The one at the back of the eye is connected to the nerve that sends information to our brain. Six external eye muscles are attached to the sclera. Thanks to them, we can move our eyes when and how we want. There are also muscles in the eyes that work automatically and we have no direct influence on them. These are, for example, the ciliary muscles, thanks to which we can see clearly at different distances.
In the front part of the sclera is the cornea, which is convex on one side. The cornea is heavily innervated, but has no blood vessels. The cornea consists of six layers: the epithelium, the Bowman layer, the essence, the Dua layer, the Descemet membrane, and the endothelium. The cornea is the part that focuses the light rays reaching the eye. Right behind it is the anterior eye chamber. There is also a posterior chamber in the eyeball. Both elements are filled with a watery liquid that nourishes our eye.
The eyeball is also associated with the pupil because it is what we can see with the naked eye. The pupils are surrounded by the iris, in which there are pigments responsible for the color of our eyes. The iris is directly in front of the lens. It is made of connective tissue. It is worth going back to the pupil. It is a black circular hole located in the center of the iris. If we look at our pupils, we can see how their size changes depending on how much light reaches them. Thus, when the intensity of the light rays is high, the pupil sphincter muscle contracts, and thus our pupils become smaller. If the intensity of the light rays is weak, the dilator of the pupil dilates and the pupil enlarges. Both of these muscles do their job automatically and we have no influence on it. It is also worth knowing that the pupils react to our emotions.
Another element of the human eye is the lens, which is transparent, flexible and able to change its shape. The lens is not made of blood vessels and nerves. The aforementioned aqueous fluid provides it with nutrients. The lens is held by the rim fibers of the ciliary muscles. If we want to clearly see something in the distance, the muscles tense and the lens flattens. When we want to look at objects closer to our eye, the ciliary muscles relax and the lens looks more like spheres.
Over the course of our life, the lens hardens, losing its elasticity. Then we notice problems with our eyesight and go to a specialist to correct the defect with glasses. The last element is the choroid, which is located at the back of our eye. It is made of a network of blood vessels, and thus – it is very well supplied with blood. Its exact position is between the sclera and the retina. There are branched veins of various sizes and arteries in the choroid. The main task of the choroid is to supply the retina with nutrients and oxygen. It is also responsible for dissipating heat from the retina. In the frontal zone of the eye, the choroid changes into the ciliary body.
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