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(Corneal Graft; Penetrating Keratoplasty; Endothelial Keratoplasty)
Corneal transplantation is a common and highly successful type of transplantation. A scarred, severely painful, perforated, misshapen, or cloudy cornea can be replaced with a clear, healthy one. Doctors using a surgical microscope carry out the procedure in about 1 hour. Donated corneas come from people who have recently died. A general or local anesthetic is used. The donated cornea is cut to the right size, the damaged cornea is removed, and the donated cornea is sewn in place. The recipient usually goes home the same day. After transplantation, people must take antibiotic eye drops for several weeks and corticosteroid eye drops for several months. An eye shield, glasses, or sunglasses must be worn. Vision is not fully improved for 6 months and as long as 18 months after transplantation.
A cornea is usually not rejected because it does not have its own blood supply. It receives oxygen and other nutrients from nearby tissues and fluid. The components of the immune system that initiate rejection in response to a foreign substance—certain white blood cells and antibodies—are carried in the bloodstream. Thus, these cells and antibodies do not reach the transplanted cornea, do not encounter the foreign tissue there, and do not initiate rejection. Tissues with a rich blood supply are much more likely to be rejected. Other problems can also occur: for example, the transplant may not work well (that is, it may become opaque and not transparent), may become infected, may cause glaucoma, and may develop incision problems. Transplants tend to be most successful when done for disorders such as bullous keratopathy, keratoconus, and certain corneal scars. They tend to be least successful when done because the cornea was damaged by a chemical or radiation.
The eye, like other living tissues, depends on continual production of new cells to replace old ones. One place that this occurs is where the cornea attaches to the conjunctiva (called the limbus). Certain kinds of injuries (for example, severe chemical burns or very severe and prolonged overwearing of contact lenses) damage these limbal stem cells so much that they can no longer produce enough new cells to keep the cornea covered. Infection and scarring can then affect the cornea. A corneal transplant does not replace the limbal stem cells and thus is of no benefit. Stem cells can be transplanted from the limbus of a person's healthy eye or a person who recently died, sometimes curing or relieving the problem.
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