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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 most common type of human transplant surgery and has the highest success rate. Eye banks acquire and store eyes from donors to supply the need for transplant corneas.


Purpose

Corneal transplant is used when vision is lost because the cornea has been damaged by disease or traumatic injury, and there are no other viable options. Some of the conditions that might require corneal transplant include the bulging outward of the cornea (keratoconus), a malfunction of the cornea's inner layer (Fuchs' dystrophy), and painful corneal swelling (pseudophakic bullous keratopathy). Other conditions that might make a corneal transplant necessary are tissue growth on the cornea (pterygium) and Stevens-Johnson syndrome, a skin disorder that can affect the eyes. Some of these conditions cause cloudiness of the cornea; others alter its natural curvature, which also can reduce vision quality.

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.

Corneal transplants are used only when damage to the cornea is too severe to be treated with corrective lenses. Occasionally, corneal transplant is combined with other eye surgery such as cataract surgery to solve multiple eye problems with one procedure.


Demographics

The Eye Bank Association of America reported that corneal transplant recipients range in age from nine days to 103 years. More than 40,000 corneal transplants are performed in the United States each year. The cost is usually covered in part by Medicare and health insurers, although the patient might be required to incur part of the cost for the procedure. All eye tissue is donated. It is illegal to buy or sell human tissue.


Description

The cornea is the transparent layer of tissue at the 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, cornea damage 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, which resembles a cookie cutter. In one form of corneal transplant, penetrating keratoplasty (PK), the disc removed is the entire thickness of the cornea and so is the replacement disc.

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 3090 minutes.

Over 90% of all corneal transplants in the United States are PK. In lamellar keratoplasty (LK), only the outer layer of the cornea is removed and replaced. LK has many advantages, including early suture removal and decreased infection risk. It is not as widely used as PK, however, because it is more time consuming and requires much greater technical ability by the surgeon.

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. This procedure is mostly performed on children. In adults, the use of contact lenses can usually achieve the same goals.


Diagnosis/Preparation

Surgeons may discuss the need for corneal transplants after other viable options to remedy corneal trauma or disease have been discussed. No special preparation for corneal transplant is needed. Some ophthalmologists may request that the patient have a complete physical examination before surgery. Any active eye infection or eye inflammation usually needs to be brought under control 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. Some patients require medication for at least a year. 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. Some surgeons may prescribe rigid contact lenses to reduce corneal astigmatism that follows corneal transplant.


Risks

Corneal transplants are highly successful, with over 90% of the 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.

Graft rejection occurs in 530% 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. Because 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. However, the Collaborative Corneal Transplantation Study found that patients at high risk for rejection could benefit from receiving corneas from a donor with a matching blood type.

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.


Normal results

Patients can expect restored vision after the healing process is complete. In some patients, this might take as long as a year. Patients with keratoconus, corneal scars, early bullous keratopathy, or corneal stromal dystrophies have the highest rate of transplant success. Corneal transplants for keratoconus patients have a success rate of more than 90%.


Morbidity and mortality rates

While there is risk involved with any surgery, corneal transplants are relatively safe. In 2001, there was some concern about cornea donors transmitting Creutzfeldt-Jakob disease, a fatal bone-deteriorating disease, after questions of infection arose in Europe. A study showed the risk of transmission in the United States was small, as was any infection risk from cornea donors. Currently, cornea donors are screened using medical standards of the Eye Bank Association of America. These guidelines restrict donors who died from unknown causes, or suffered from immune deficiency diseases, hepatitis, and other infectious diseases.

Transplant recipients may have to receive another transplant if the first is unsuccessful or if, after a number of years, the disease returns.

Alternatives

An increasingly popular alternative to corneal transplants is phototherapeutic keratectomy (PTK). This technique is now used to treat corneal scars and dystrophies, and some infections. Surgeons use an excimer laser and a computer to vaporize diseased tissue, leaving a smooth surface. New tissue begins growing immediately and recovery takes only a few days. Patients must be carefully selected, however, and success is greatest if damage is restricted to the cornea's top layer.

Intrastromal corneal rings are implantable devices that could be used for some keratoconus patients. The rings are implanted and the procedure is reversible. However, not much is known about long-term stability. Some companies also are developing synthetic corneas that are implanted using synthetic penetrating keratoplasty. This procedure may become more widely used for high-risk patients and those with severe chemical burns.


Resources

books

Boruchoff, S. Arthur, and Richard A. Thoft. "Keratoplasty: Lamellar and Penetrating." In The Cornea, edited by 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.

Miller, Stephen J. H. Parsons' Diseases of the Eye, 18th ed. New York: Churchill Livingstone, 1990.

Vaughan, Daniel, ed. General Ophthalmology, 14th ed. Stamford: Appleton & Lange, 1995.


periodicals

Kennedy, R. H., et al. "Eye Banking and Screening for Creutzfeldt-Jakob Disease." Archives of Ophthalmology 119 (May 2001): 7216.

Watson, B. C., and G. L. White Jr. "Corneal Transplantation." American Family Physician 54 (Nov. 1996): 194548.


organizations

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

Eye Bank Association of America. 1015 Eighteenth Street NW, Suite 1010, Washington, D.C. 20036. (202) 775-4999. <http://www.restoresight.org>.


other

Asbell, Penny A., and Syed M. Ahmad. "New Techniques in Corneal Transplant." Review of Ophthalmology, May 15, 2002 [cited February 20, 2003]. <www.revophth.com/index.asp?page=1_94.htm>.

Cimberle, Michela. "New Type of Artificial Cornea Performs Better than Donor Grafts in High-Risk Cases." Ocular Surgery News, June 1, 2002 [cited February 23, 2003]. <www.osnsupersite.com/view.asp?ID=2346>.

"Collaborative Corneal Transplantation Studies." National Eye Institute, October 21, 1999 [cited February 25, 2003]. <www.nei.nih.gov/neitrials/statics/study36.htm>.

"Corneal Transplantation." Merck Manual of Diagnosis and Therapy, [cited February 25, 2003]. <www.merck.com/pubs/mmanual/section8/chapter96/96l.htm>.

"Facts About the Cornea and Corneal Disease." National Eye Institute, June 2001 [cited March 4, 2003]. <www.nei.nih.gov/health/cornealdisease/index.htm>.


Victor Leipzig, PhD Mary Bekker

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?


Corneal transplants are performed by an ophthalmologist, who is a corneal specialist and is expert at transplants and corneal diseases. Patients might be referred to a corneal specialist by their ophthalmologist or optometrist.

Surgery is performed in a hospital setting, usually on an outpatient basis. Some surgeons may also perform the procedure at an ambulatory surgery center designed for outpatient procedures.

QUESTIONS TO ASK THE DOCTOR


  • Are there any alternatives that might restore my vision?
  • What is the chance of rejection?
  • How am I matched with the donor corneas?
  • What is the screening process for donors?
  • What physical restrictions will I have during the healing process?
  • What are the chances of eye injury causing rejection?
  • If the transplant is successful, how long will it be until vision is restored?
  • Will I ever have to have another transplant?

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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.

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epikeratophakia

epikeratophakia (epi-ke-ră-toh-fay-kiă) n. eye surgery to correct errors of refraction in which the curvature of the cornea is altered using donor corneal tissue, which has been frozen and shaped using a lathe to produce a tissue lens that is then sutured onto the cornea.

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keratoplasty

keratoplasty (corneal graft) (ke-ră-toh-plasti) n. an eye operation in which any diseased parts of the cornea are replaced by clear corneal tissue from a donor.

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