Corneal Transplantation


Corneal Transplantation

 

Definition

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.Cornea donors are carefully screened. Individuals with infectious diseases are not accepted as donors.

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.

Resources

Organizations

American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. http://www.eyenet.org.

corneal

 [kor´ne-al] pertaining to the cornea.corneal reflex a reflex action of the eye resulting in automatic closing of the eyelid when the cornea is stimulated. The corneal reflex can be elicited in a normal person by gently touching the cornea with a wisp of cotton. Absence of the corneal reflex indicates deep coma or injury of one of the nerves carrying the reflex arc.corneal transplantation transplantation of a donor cornea into the eye of a recipient, done to improve the vision of patients with distorted curvature of the cornea (keratoconus) or corneal edema, infection, trauma, or intractable pain. Vision should improve beginning the day after surgery with optimal vision 6 to 12 months later. Because the cornea does not have a blood supply, corneal transplants were one of the earliest successful types of organ transplants. Called also keratoplasty.

transplantation

 [trans″plan-ta´shun] the transfer of living organs or tissue from one part of the body to another or from one individual to another. Transplantation and grafting mean the same thing, although the term grafting is more commonly used to refer to the transfer of skin. In dentistry, transplantation refers to the insertion into a prepared dental alveolus of an autogenous or homologous tooth; it may be a developing tooth germ from the same mouth, or a frozen homologous transplant.

Occasionally an emergency requires an organ to be transplanted from one place to another within the body. Kidneys, for example, have been relocated to enable them to continue functioning after the ureters have been damaged. Transplantation of an organ within the body, known as autotransplantation" >autotransplantation or an graft" >autologous graft, requires delicate surgery but otherwise poses no particular problem.
Eye surgeons have developed the procedure called corneal transplantation" >corneal transplantation or keratoplasty, in which part or all of a diseased cornea that has become opaque is removed and replaced by healthy corneal tissue from an eye bank. Cartilage and bone are other tissues that are not difficult to transplant from one individual to another. Cartilage is particularly able to be made into various shapes and so is widely used in reconstructive surgery. Bone grafts are sometimes used instead of metal plates in operations to repair fractures, and they can also be used to replace diseased bone. Grafts made of synthetic materials may also be used, such as Dacron vascular grafts that replace parts of blood vessels.
Kidney transplants have been performed on dogs since 1902, but remained in the experimental realm in humans until a ground-breaking operation was performed in 1954 in Boston. A kidney from one identical twin was successfully implanted in the other to replace his diseased kidneys. Since that time kidney transplantations have been the most successful of transplantations, primarily because there are artificial kidney machines available (see dialysis and hemodialysis), and also because the kidney is a paired organ. This means that the donor need not be cadaveric but can be a living person (such as a relative of the recipient) and can be selected on the basis of tissue-type compatibility to avoid fatal rejection of the organ by the recipient.
In 1967 the South African surgeon Christiaan N. Barnard transplanted a human heart. Transplants of hearts and other vital organs are now being done at an increasing rate throughout the world. There are ethical and legal implications of obtaining healthy organs for transplantation, which still have not been completely resolved.Rejection. The major problem to be overcome in transplantation therapy is rejection, an immune phenomenon. Organs such as the cornea, skin, and bone can be transplanted successfully because, in the case of the cornea, the vascular supply is not involved, or, in skin and bone, the transplant serves as a structural foundation into which the new tissue grows. In the case of intact organs such as the kidney, heart, lung, liver, and pancreas, a generous blood supply is essential to their survival in the recipient's body. The blood of the recipient carries in it many of the tools used by the body in defense against foreign substances. As blood is drained from the transplanted organ into the host's general circulation, the body recognizes the transplanted tissue cells as foreign invaders (antigens) and immediately sets up an immune response by producing antibodies. These antibodies are capable of inhibiting metabolism of the cells within the transplanted organ and eventually actively cause their destruction. They also play a role in delayed response" >inflammatory response that can occur as late as weeks or months after implantation and adds to the destruction of the donor organ.

In order to minimize rejection and improve the chances of survival of a transplanted organ, efforts are made to match as closely as possible the blood types and tissue types of the donor and recipient. First, the blood is tested for ABO or blood type compatibility. Then, tissue typing is done to identify the protein antigens that are specific to each individual. These antigens are the hla antigens (HLA), so called because they are easily identifiable on leukocytes. The more compatible these antigens are between donor and recipient, the less likely tissue rejection will occur. A third test that is done is crossmatching, which involves mixing the intended recipient's serum with lymphocytes from the potential donor. A positive reaction would show destruction of the donor's cells by antibodies in the recipient's serum, thus eliminating the possibility of using an organ from that particular donor. The probability of survival of a transplanted organ is highest when the donor is a sibling who is HLA identical to the recipient.
Control of the immune response in the recipient is attempted by the use of immunosuppressive agents such as globulin" >antilymphocyte globulin and antimetabolites, which tend to suppress the growth of rapidly dividing cells, and cyclosporine, which inhibits T-cell function. corticosteroids also are used because of their antiinflammatory effect. All of the chemicals used in transplantation therapy interfere in some way with the body's normal defense mechanisms. For this reason a delicate balance must be maintained in their administration so as to avoid tipping the scales either in the direction of rejection of the organ on one side or a fatal infection on the other.Heart transplantation. From Ignatavicius and Workman, 2000.allogeneic transplantation transplantation of an allograft; the three types are cadaveric donor, living related donor, and living unrelated donor transplantation. Called also allotransplantation.bone marrow transplantation the intravenous infusion of marrow" >bone marrow; the marrow may be autologous" >autologous (from a previously harvested and stored self-donation) or allogeneic (from a living related donor or a living unrelated donor). Used to treat malignancies such as leukemia, lymphoma, myeloma, and selected solid tumors, as well as nonmalignant conditions such as aplastic anemia, immunologic deficiencies, and errors of metabolism" >inborn errors of metabolism.cadaveric donor transplantation allogeneic transplantation of an organ or tissue from a cadaver.corneal transplantation transplantation of a donor cornea into the eye of a recipient; see also corneal transplantation.heterotopic transplantation transplantation of tissue typical of one area to a different recipient site.homotopic transplantation orthotopic transplantation.living nonrelated donor transplantation living unrelated donor transplantation.living related donor transplantation allogeneic transplantation in which the donor and the recipient have a close biological relationship, such as that of a parent and child or a brother and sister.living unrelated donor transplantation allogeneic transplantation in which the donor and the recipient do not have a close biological relationship.orthotopic transplantation transplantation of tissue from a donor into its normal position in the body of the recipient.syngeneic transplantation living related donor transplantation in which the organ or tissue is a syngraft; called also isotransplantation.xenogeneic transplantation transplantation of a xenograft; called also heterotransplantation.

ker·a·to·plas·ty

(ker'ă-tō-plas'tē), Any surgical modification of the cornea; the removal of a portion of the cornea containing an opacity and the insertion in its place of a piece of cornea of the same size and shape removed from elsewhere. Synonym(s): corneal graft, corneal transplantation, corneal trepanation, trepanation of cornea, transplantation of cornea [kerato- + G. plassō, to form]

Patient discussion about Corneal Transplantation

Q. Has anyone had experience with a corneal transplant because of keratoconus? A. my uncle had to do a transplant- it took 5 weeks until he could see anything , another year to get his vision straightened up. but now he is fine! i know that he looked for information in the "National Keratoconus Foundation". they were very helpful (and nice!), they have a website with information on all forms of treatment:
http://www.nkcf.org/
good luck :)

More discussions about Corneal Transplantation