One of the most important parts of the human eye is the cornea, which protects it from damage and infections. However, she herself is very vulnerable, prone to various diseases.
The cornea of the eye protects its anterior part and is the outer domed surface of the eye; it does not contain the blood vessels necessary for the nutrition of most tissues of the human body; it is distinguished by optical homogeneity. In order to qualitatively refract light, the cornea must be transparent, the presence of even very small vessels will interfere with this process. The refractive index of the cornea is 43 diopters. It receives its nutrition mainly from tears and aqueous humor located in the anterior chamber.
The cornea of the eye is often compared with a watch glass inserted in the frame, since the curvature of the cornea itself is slightly greater than the curvature of the sclera. The cornea consists of five layers, each having its own important function: the epithelium, Descemet's membrane, Bowman's layer, endothelium, and stroma.
The anterior layer - the epithelium - is formed from multifaceted flat cells. Next comes the Bowman layer - a homogeneous structureless front boundary plate. Actually, the corneal substance itself is called the stroma, it consists of the thinnest connective tissue plates, alternating among themselves, containing many of the thinnest fibrils. A mucoid, which incorporates sulfohyaluronic acid, which ensures the transparency of the cornea, acts as a bonding agent. The stroma does not contain blood vessels and is very slowly restored. Descemet's membrane, or membrane, is a back, very dense, border plate, its fibrils consist of a special substance that is identical to collagen; it regenerates well. The endothelium (or posterior corneal epithelium) is a layer of flat hexagonal prismatic cells closely adjacent to each other. This layer is responsible for the transparency of the cornea and is not restored at all.
The cornea contains 80% water, 18% definitive collagen, about 2% mucopolysaccharides, lipids, proteins, vitamins C, B, etc. In older people, the cornea of the eye contains much less vitamins and moisture, globulin fractions of protein predominate in it, and also lipids and calcium salts are deposited. The consequence of such changes is a change in the transition of the cornea (limb) to the sclera - the scleral layers begin to “move” onto the cornea and the so-called senile arch appears, the sensitivity of the cornea and its refractive power decrease. In addition, its permeability to eye drops, ointments and nutrients is significantly reduced.
Sensitivity of the cornea of the eye (innervation) by the trigeminal nerve. Especially a lot of nerve endings in the surface layers, least of all - in the endothelium. In newborns, the cornea of the eye is insensitive due to the incomplete development of cranial nerves, and at the age of one year its sensitivity is almost the same as in adults.
Due to the fact that the cornea is the outer shell of the eye, it is constantly in contact with the external environment. Therefore, there are special protection mechanisms against harmful effects from outside and injuries:
- Reflex eye closure;
- Washing off harmful agents from the surface of the cornea using tear fluid;
- Fast and complete restoration of the epithelium.
The main diseases of the cornea are: developmental abnormalities, dystrophic and inflammatory processes (scleritis, keratitis) and tumors.
Among pathologies, inflammation of the cornea of the eye or keratitis is most common. Keratitis is exogenous and endogenous. Very often after keratitis, clouding of the cornea of the eye of varying severity remains. The intensity of turbidity and its size distinguish turbidity in the form of a thorn, spot and cloud. Belmo is a persistent opacification of the cornea of the eye, which is caused by a cicatricial change, occupying part of the cornea or the entire cornea. A spot is a persistent intense clouding of the cornea with clear edges at the periphery or in the center. The cloud is a limited gray haze that is barely visible on examination.