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2023 Author: Alfred Shackley | [email protected]. Last modified: 2023-05-21 13:14
Perhaps you still do not know what it is - the cornea of the eye? This is the outer shell of the eye, or rather, its part that has transparency. In shape, it resembles a watch glass, and is the main medium in the optical system of the organ of vision.
If the cornea is functioning normally, then the visual images will be correctly transmitted to the brain. Any pathology affects the reliability of the information. Complications associated with diseases of the cornea can lead to poor vision and even complete loss of vision.
The outer capsule of the eye is 17% covered with the cornea. The thickness of the convex-concave lens in an adult in the central part is 450-600 microns, on the edge - at the periphery - 650-700 microns.
In the center, the thickness of this part of the outer ocular membrane is 0.5 mm, and at the edge - no more than 1.2 mm. It is this structure that provides the refraction of light rays: the refractive index is 1.37 diopters, and the refractive power is 40 diopters.
All convex-concave lenses have one very important parameter that characterizes the refraction of the light flux - the radius of the stratum corneum. With a healthy optical system in humans, this radius is usually about 7, 8 mm.
There are many nerve endings in the thickness of the cornea, as a result of which it has a high sensitivity.
To understand why the integrity of the transparent shell is so important for the body, it is necessary to know its structure.
- The upper layer is epithelial. Its functions are protective: it provides oxygen supply and normalizes the amount of intraocular fluid.
- Bowman's membrane is a nutritional function. If it is damaged, recovery is impossible.
- The stroma is the widest layer. It consists of horizontal collagen fibers and cells: keratocytes, fibrocytes and leukocytes.
- Descemet's membrane - consists of strong and elastic cell layers.
- Endothelium - the inner epithelial layer is interesting in that the epithelial cells in it have the shape of a hexagon. Its function is to ensure the outflow of intraocular fluid. Thanks to this layer, the cornea remains transparent. Does not have the ability to recover.
The anterior epithelium is absolutely smooth, connected with the conjunctiva, and is permeable to gases and liquids. It is thanks to the permeability of the anterior epithelium that medicine has the ability to treat eye diseases with topical agents - drops and ointments.
The posterior epithelium along the periphery of the cornea is connected to the trabecular network and passes to it.
If we fully consider the structure of the stratum corneum, then one more should be mentioned - the tear film. If it does not constantly wash the surface of the eyeball, the functioning of the entire organ of vision is disrupted.
Examination of the endothelium is carried out using a mirror microscope - without it, it is impossible to see the epithelial cells, thanks to which the endothelium self-repairs. At the age of 16, a person has 3700 of these cells - the ability to regenerate is the highest, and with age, their number decreases. If the endothelium is injured, then the fluid from the anterior chamber will penetrate into all layers of the membrane, and the cornea will become cloudy.
The structure of the cornea allows the eyes to provide the main function of the organ of vision - the ability to perceive information. A camera lens has a similar structure and action - it collects light rays and focuses them. There would be no refractive medium, it would be impossible to see.
Corneal abnormalities and diseases
If the normal structure of the stratum corneum is disturbed, then pathological changes relate to its size, shape and light transmission.
Most common abnormalities.
- Megalocornea - that is, the cornea grows and becomes much thicker. This anomaly can develop against the background of glaucoma.
- Microcornea - this anomaly is one- and two-sided, the eyeball also decreases in size, the likelihood of subatrophy of the eyeball increases.
- Embryotoxone is an annular opacity in a transparent membrane that is located along the limbus, resembling an arc that appears in old age. No treatment is required, it does not affect the function of the organ of vision.
- Keratoconus is a hereditary anomaly, the cornea is thinned, its structure is disturbed, it is elongated in the shape of a cone, and loses its elasticity. Pathology is bilateral.
- Acute keratoconus - cracks in the Descemet's membrane.
- Weakness of the elastic frame - an anomaly of the stratum corneum causes astigmatism, if treatment does not start on time, the disease progresses and keratoconus appears.
- Keratoglobus is a spherical cornea that appears with genetic disorders and is inherited.
All inflammatory processes of the optic organ affect the stratum corneum or develop directly in it. Also, inflammation can be provoked by dermatological and infectious processes on the eyelids or arising in the area around the eyes.
Most often, diseases occur with anomalies of the stratum corneum - keratoglobus, allergens, chemicals, environmental factors - dust and chemicals dispersed in the air - have a negative effect. All adverse effects reduce the transparency of the cornea.
Traumatic lesions - regardless of the nature of the damage - can provoke the appearance of an ulcerative defect in the stratum corneum. If Descemet's membrane is able to withstand the "pressure" of destructive factors, then the visual function is preserved. Injuries with a similar symptom - ulceration - are more likely to cause penetrating effects caused by foreign bodies, or burns - chemical or thermal. Unfortunately, ulcerative defects are not always treatable - in this case, necrosis of individual elements of the eye may occur.
The most dangerous infectious processes are caused by fungal flora, which is actively developing in the eye - there are suitable conditions for it: the required temperature and humidity.
Mycoses are very difficult to cure. The fungal flora does not react to antibacterial and antiviral agents, and while waiting for the result of scraping from the eyelid, the disease can reach a serious stage. Antimycotic drugs - drops and ointments - are made according to individual recipes.
Features of corneal lesion
Eye diseases seriously affect human life - even a slight decrease in vision has a negative impact on the quality of life.
The defeat of the stratum corneum is always a decrease in visual acuity. If treatment is not started on time, illnesses can lead to partial or complete blindness.
Eye examinations should be done regularly. Until the age of 45, it is enough to consult an ophthalmologist once a year, after 45 - 3 times every 2 years.
Especially rapidly developing eye diseases in women who have entered the postmenopausal age.
Diseases of the stratum corneum are asymptomatic. Signs of damage: photosensitivity or photophobia, lacrimation. Hypersensitivity of the cornea is an indicator of the degree of development of pathologies.
If the lesions extend to the function of light refraction, then vision is corrected using optical instruments. Clouding and eyesore cannot be eliminated without surgery.