Cornea

What exactly is the cornea?

The cornea is the clear "window" of the eye in the world. This anterior layer of tissue is the most refractive surface of the eye and it is responsible for the precise focusing of the light rays on the retina, which in turn translates light into optical stimulus.

cornea1   cornea2

Corneal layers

The cornea is comprised of the following layers:

  • Epithelium
  • Bowman's membrane
  • Stroma
  • Descemet Membrane
  • Endothelium

cornea3   cornea4

Usually the thickness of the cornea is between 450 and 620 microns. Pachymetry is very important information in a refractive test since it is a key criterion of selecting a technique in case of a refractive surgery with laser (LASIK, PRK). Any blurring or change in corneal curvature has a direct effect on the quality of vision.

Conditions and dystrophies

Corneal conditions:

Because the cornea is exposed (not continuously protected by the eyelids) it is easy to be injured or infected. Thus trauma, infections, hereditary disease is able to cause blurring, distortion or scarring in the cornea. When the cornea becomes cloudy, light can not pass through the eye and reach the retina. The result is the vision reduction (in extreme cases, blindness). The cornea has many superficial nerves resulting in severe pain in minimal injury. The existence of normal tear protects corneal drying and infections, thus the tear deficiency is capable of causing problems in the corneal layers.

cornea5   cornea6

There are many diseases and corneal dystrophies, the most important are the ones below:

  • Keratoconus: a fairly common condition in which the cornea of the eye gradually takes a rough cone shape and can cause severe disturbance of the vision due to the creation of irregular astigmatism
  • Peripapillary senile halo: it is the most common peripheral corneal clouding with the appearance of lipid deposits. It is age-related and it is found in virtually all people over 80 years
  • Keratoglobus: a rare condition which starts at birth. It is characterized by thinning of the cornea at the ends. In some cases caused rupture of the Descemet membrane or even rupture of the whole cornea due to its fineness
  • Endothelial Fuchs dystrophy (Fuchs dystrophy): refers to the swelling of the core layer of the cornea due to the non-replacement of endothelial cells resulting in turbidity of sight

Treatment

Permanent turbidity mainly on the central axis of the cornea, is treated only by surgical corneal transplant procedure (keratoplasty), i.e. by replacing the diseased cornea (or portion thereof) from the human donor cornea (suitable graft). Nowadays various techniques of corneal transplantation are used (keratoplasty), always depending on the incident. 

cornea7   cornea8