The transparent layer in front of the iris, the colored part of the eye, is called the cornea. After the rays coming to the eye first pass through this tissue, they reach the nerve layer we call the retina and vision takes place.

The transparency or regular shape of the cornea therefore plays an important role in vision. If the cornea loses its transparency (hereditary diseases such as corneal dystrophy, corneal edema that does not go away after cataract surgery, etc.) or deforms (progressive thinning and erection of the cornea such as keratoconus), the patient cannot see clearly.

In such cases, vision can be regained by replacing the cornea with another healthy corneal tissue. In this transplant process, the tissue is healthy corneal tissue taken from a deceased person and the process is called corneal transplant.