In corneal transplant, also known as keratoplasty, a patient's damaged cornea is replaced by the cornea from the eye of a human cadaver. This is the single most common type of human transplant surgery and has the highest success rate. Eye banks acquire and store eyes from donor individuals largely to supply the need for transplant corneas.
Purpose
Corneal transplant is used when vision is lost in an eye because the cornea has been damaged by disease or traumatic injury. Some of the disease conditions that might require corneal transplant include the bulging outward of the cornea (keratoconus), a malfunction of the inner layer of the cornea (Fuchs' dystrophy), and painful swelling of the cornea (pseudophakic bullous keratopathy). Some of these conditions cause cloudiness of the cornea; others alter its natural curvature, which can also reduce the quality of vision.
Injury to the cornea can occur because of chemical burns, mechanical trauma, or infection by viruses, bacteria, fungi, or protozoa. The herpes virus produces one of the more common infections leading to corneal transplant.
Surgery would only be used when damage to the cornea is too severe to be treated with corrective lenses. Occasionally, corneal transplant is combined with other types of eye surgery (such as cataract surgery) to solve multiple eye problems in one procedure.
Precautions
Corneal transplant is a very safe procedure that can be performed on almost any patient who would benefit from it. Any active infection or inflammation of the eye usually needs to be brought under control before surgery can be performed.
Description
The cornea is the transparent layer of tissue at the very front of the eye. It is composed almost entirely of a special type of collagen. It normally contains no blood vessels, but because it contains nerve endings, damage to the cornea can be very painful.
In a corneal transplant, a disc of tissue is removed from the center of the eye and replaced by a corresponding disc from a donor eye. The circular incision is made using an instrument called a trephine. In one form of corneal transplant (penetrating keratoplasty), the disc removed is the entire thickness of the cornea and so is the replacement disc. Over 90% of all corneal transplants in the United States are of this type. In lamellar keratoplasty, on the other hand, only the outer layer of the cornea is removed and replaced.
The donor cornea is attached with extremely fine sutures. Surgery can be performed under anesthesia that is confined to one area of the body while the patient is awake (local anesthesia) or under anesthesia that places the entire body of the patient in a state of unconsciousness (general anesthesia.) Surgery requires 30–90 minutes.
Over 40,000 corneal transplants are performed in the United States each year. Medicare reimbursement for a corneal transplant in one eye was about $1,200 in 1997.
A less common but related procedure called epikeratophakia involves suturing the donor cornea directly onto the surface of the existing host cornea. The only tissue removed from the host is the extremely thin epithelial cell layer on the outside of the host cornea. There is no permanent damage to the host cornea, and this procedure can be reversed. It is usually employed in children. In adults, the use of contact lenses can usually achieve the same goals.
Preparation
No special preparation for corneal transplant is needed. Some eye surgeons may request the patient have a complete physical examination before surgery. The patient may also be asked to skip breakfast on the day of surgery.
Aftercare
Corneal transplant is often performed on an outpatient basis, although some patients need brief hospitalization after surgery. The patient will wear an eye patch at least overnight. An eye shield or glasses must be worn to protect the eye until the surgical wound has healed. Eye drops will be prescribed for the patient to use for several weeks after surgery. These drops include antibiotics to prevent infection as well as corticosteroids to reduce inflammation and prevent graft rejection.
For the first few days after surgery, the eye may feel scratchy and irritated. Vision will be somewhat blurry for as long as several months.
Sutures are often left in place for six months, and occasionally for as long as two years.
Risks
Corneal transplants are highly successful, with over 90% of operations in United States achieving restoration of sight. However, there is always some risk associated with any surgery. Complications that can occur include infection, glaucoma, retinal detachment, cataract formation, and rejection of the donor cornea.
Graft rejection occurs in 5–30% of patients, a complication possible with any procedure involving tissue transplantation from another person (allograft). Allograft rejection results from a reaction of the patient's immune system to the donor tissue. Cell surface proteins called histocompatibility antigens trigger this reaction. These antigens are often associated with vascular tissue (blood vessels) within the graft tissue. Since the cornea normally contains no blood vessels, it experiences a very low rate of rejection. Generally, blood typing and tissue typing are not needed in corneal transplants, and no close match between donor and recipient is required. Symptoms of rejection include persistent discomfort, sensitivity to light, redness, or a change in vision.
If a rejection reaction does occur, it can usually be blocked by steroid treatment. Rejection reactions may become noticeable within weeks after surgery, but may not occur until 10 or even 20 years after the transplant. When full rejection does occur, the surgery will usually need to be repeated.
Although the cornea is not normally vascular, some corneal diseases cause vascularization (the growth of blood vessels) into the cornea. In patients with these conditions, careful testing of both donor and recipient is performed just as in transplantation of other organs and tissues such as hearts, kidneys, and bone marrow. In such patients, repeated surgery is sometimes necessary in order to achieve a successful transplant.
Boruchoff, S. Arthur, and Richard A. Thoft. "Keratoplasty: Lamellar and Penetrating." In The Cornea, ed. Gilbert Smolin and Richard A. Thoft. Boston: Little, Brown and Co., 1994.
Brightbill, Frederick S., ed. Corneal Surgery. St. Louis: Mosby, 1993.
Bruner, William E., Walter J. Stark, and A. Edward Maumenee. Manual of Corneal Surgery. New York: Churchill Livingstone, 1987.
General Ophthalmology. 14th ed. Ed. Daniel Vaughan. Stamford: Appleton & Lange, 1995.
Miller, Stephen J. H. Parsons'Diseases of the Eye. 18th ed. New York: Churchill Livingstone, 1990.
PERIODICALS
Watson, B. C., and G. L. White Jr. "Corneal Transplantation." American Family Physician 54 (Nov. 1996): 1945-1948.
ORGANIZATIONS
American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. <http://www.eyenet.org>.
Victor Leipzig, PhD
KEY TERMS
Cadaver—The human body after death.
Cataract—A condition of cloudiness of the lens of the eye.
Cornea—The transparent layer of tissue at the very front of the eye.
Corticosteroids—Synthetic hormones widely used to fight inflammation.
Epikeratophakia—A procedure in which the donor cornea is attached directly onto the host cornea.
Epithelial cells—Cells that form a thin surface coating on the outside of a body structure.
Fibrous connective tissue—Dense tissue found in various parts of the body containing very few living cells.
Fuchs' dystrophy—A hereditary disease of the inner layer of the cornea. Treatment requires penetrating keratoplasty. The lens of the eye may also be affected and require surgical replacement at the same time as the cornea.
Glaucoma—A vision defect caused when excessive fluid pressure within the eye damages the optic nerve.
Histocompatibility antigens—Proteins scattered throughout body tissues that are unique for almost every individual.
Keratoconus—An eye condition in which the cornea bulges outward, interfering with normal vision. Usually both eyes are affected.
Pseudophakic bullous keratopathy—Painful swelling of the cornea occasionally occurring after surgery to implant an artificial lens in place of a lens affected by cataract.
Retinal detachment—A serious vision disorder in which the light-detecting layer of cells inside the eye (retina) is separated from its normal support tissue and no longer functions properly.
Trephine—A small surgical instrument that is rotated to cut a circular incision.
