Cornea (Latin cornea ) is the front transparent part of the outer membrane of the eye and is also the first optical medium that light rays reach on the way through the eye.
Its role is refraction of light, i.e. refraction of the eye. It is transparent like glass due to a certain amount of water in it, there are no blood vessels, and nerve fibers do not have a myelin sheath.
It gets nutrients from tears on the outside and aqueous humor on the inside. The cornea passes into the sclera at the edge. The front surface of the cornea borders the outer space and is convex, while the back surface of the cornea is concave. This actually gives us an optical lens with a strength of approx. 43 diopters. Proper bulging is an essential feature of the cornea. If the curvature of the cornea is unequal in two mutually perpendicular meridians, astigmatism occurs because the rays cannot meet at one point. The radius of curvature of the cornea is 7.8 mm. In humans, the cornea has a diameter of about 11.5 mm. If the diameter is less than 10 mm, we speak of a small cornea ( microcornea ), if it is greater than 13 mm, then we speak of a large cornea ( megalocornea ).
The thickness of the cornea is different, at the ends it is about 1.0 mm, and in the center it is thinner and about 0.7 mm. A degenerative disease of the cornea in which the cornea thins in one place and bulges is called keratoconus. Similar to keratoconus is keratoglobus, and the difference is that in keratoglobus the entire cornea is bulging, not just one part of it. The thickness of the cornea is an important criterion in candidates for laser diopter reduction (LASIK), because the operation is performed on the cornea.
Going from the front to the back surface, we distinguish 5 layers inside the cornea:
- Multilayered squamous epithelium
- Bowman’s basement membrane
- Substantia propria – stroma
- Descemet’s membrane
- Endothelium, single-layer lamellar
Corneal diseases:
Inflammation of the cornea (keratitis) – we distinguish between infectious and non-infectious causes of keratitis.
We divide infectious keratitis into:
- Bacterial keratitis
- Viral keratitis
- Fungal keratitis
We call non-infectious keratitis keratopathies. The cause is a whole series of factors that weaken the cornea and contribute to its disease.
Autor:
Bc. Livio Svržnjak, optometrist
