It is the transparent tissue in the anterior part of the eye specialised for focusing the light.

It enables the light coming from outer environment to be efficiently focussed on the retina.

Cornea, has to be transparent for proper refraction of light. Therefore there are no blood vessels in its structure.

Cornea is very sensitive to external factors as it involves many nerve fibres in its structure.

Cornea may be affected by disease-causing factors just as all living tissues.

The shape and transparency of the cornea may be damaged following congenital diseases. For instance, congenitally the cornea may be smaller than the normal and this case is called microcornea.

The inflammation of the cornea is called keratitis.

Rheumatic diseases may damage the cornea. For instance, rheumatoid arthritis may be threatening by reducing the moisture in the cornea.

The cornea may be also affected by allergic diseases. For instance, vernal conjunctivitis, a type of allergic diseases, may cause damages in the cornea.

Keratoconus is a disease appearing as a thinned or conically pointed cornea and related high degrees of astigmatism and visual impairment (see the title Keratoconus).

The cornea may be exposed to injuries as it is situated in the outmost part of the eye part of the eye.

The integrity of the eyeball may be damaged following corneal traumas and this is a case that should be immediately treated.

The most important thing to do after the contact of eyes with acids or alkaline substances is to immediately wash the eyes with plenty of water and consult a medical centre with required equipment. It may be required that the eyes be washed with litres of water and the eyelids should be turned inside out and remaining residues of the chemical substance should be certainly removed.

Cornea surgery is performed for the purposes of changing the integrity, transparency or optical features of the cornea.

Corneal transplantation (keratoplasty) is a transplantation surgery with a higher chance of success. Lamellar keratoplasty is changing the half layer of the corneal tissue. Penetrating keratoplasty is changing the full layer of the corneal tissue.

Nowadays cornea surgeries are also widely performed to correct defects of myopia, hyperopia and astigmatism.