The cornea is the clear covering of the eyeball. With corneal transplantation, a part of a person's cornea is removed. It is then replaced with a portion of a cornea from a donor eye. In some cases, only the surface portion of the cornea needs to be removed. This is referred to as lamellar keratoplasty. In the majority of cases, however, the entire thickness of the cornea must be replaced. This is called penetrating keratoplasty.
Conditions that make corneal transplant necessary include: irregularities on the surface of the cornea, most commonly keratoconussevere corneal ulcers or infectioncorneal injury, damage, or scarringdense clouding of the corneal tissue that reduces vision in the elderly, called Fuch's dystrophy
This procedure should be done only if a person's vision cannot be corrected with medical treatment or contact lenses.
Corneal transplant tissue comes from people who have died, and donated their organs or tissue. This tissue is kept in an "eye bank" In lamellar keratoplasty, the diseased or opaque surface of the person's cornea is removed. It is replaced with piece of clear cornea in a similar shape and thickness. The partial thickness of cornea is then sewn onto the person's own cornea. In a penetrating keratoplasty, an instrument called a trephine is used to remove a button of scarred cornea from the person's eye. A similar sized graft from a donor eye is sewn in its place. Most corneal transplants are done under local anesthesia in a same day surgery setting.
The Merck Manual of Medical Information, Home edition, 1997