The prospect of a cornea transplant might be frightening, but it is among the most common and successful transplant procedures performed today. The surgeon removes some or all of the clear tissue at the front of the eye and replaces it with tissue from a donor. The procedure can restore sight for people who have vision loss because of damage to their cornea.
Yale Medicine's eye specialists have a wealth of experience in the evaluation and management of various diseases affecting the cornea, says Jessica H. Chow, MD, a physician with Yale Medicine Ophthalmology. We use state-of-the-art diagnostic tools, and offer the latest, most advanced care for both straightforward and complex cornea transplant procedures.
What is the cornea and why are cornea transplants important?
The cornea is the clear tissue at the front of the eye, above the iris and pupil. It is responsible for focusing light toward the retina at the back of eye. Although the cornea may appear to be a simple structure, it actually comprises three primary layers of tissue, each with its own function.
The outermost layer, the epithelium, protects the eye and absorbs oxygen and nutrients from tears; a smooth epithelial layer is crucial for clear vision. The middle layer, the stroma, provides the structure and integrity of the cornea. The innermost layer, the endothelium, maintains the fluid balance within the cornea.
If any one of the layers is damaged or diseased, or if the cornea is not clear, vision can be impaired.
Why are corneal transplants performed?
Corneal transplants are performed for many different reasons, including trauma, infection or diseases that damage any part of the cornea.
Many corneal transplants are performed in patients with Fuchs’ dystrophy, a condition in which the innermost layer of the cornea, the endothelium, deteriorates. The endothelium sits at the very back of the cornea, on top of a layer of intraocular fluid that nourishes the rest of the cornea. Normally, the endothelium cells are responsible for maintaining the proper fluid balance within the cornea. Fuchs’ dystrophy causes fluid to build up within the cornea, which causes corneal swelling and decreases vision.
Another condition that is often treated with a corneal transplant is keratoconus, a degenerative condition that leads to a cone-shaped cornea and vision impairment. If the condition progresses to the point where specialty contact lenses no longer help, a cornea transplant may be performed.
How are corneal transplants performed?
“Cornea transplantation has changed significantly over the last 20 years,” says Dr. Chow. “Previously, when someone had a cornea transplant, replacing the entire thickness of the cornea was the only option. Now, we can replace just the front layers of the cornea, the back layers of the cornea, or the entire cornea. Thinner and thinner transplants are being performed.”
Transplanting less tissue helps preserve the integrity of the eye, lowers the risk of failure or rejection of the graft (the living tissue that is implanted), and speeds up the recovery period.
“The type of transplant depends on which layers are defective and need to be replaced,” Dr. Chow says. For a patient with Fuchs’ dystrophy, only the inner layer of the cornea is damaged. It can be transplanted using one of two methods:
DSAEK: In the procedure called Descemet’s stripping automated endothelial keratoplasty (DSAEK), the damaged endothelium and the very thin membrane that separates it from the middle of the cornea are removed. Then, an 80 to 120-microns thickness of donor cornea is transplanted. For reference, an entire healthy cornea is about 540 microns (one-half of a millimeter) thick.
DMEK: A newer method of transplanting the inner layer, Descemet’s membrane endothelial keratoplasty (DMEK), involves transplanting only a single layer of cells. “When less tissue is transplanted, the patient will end up with better vision sooner,” Dr. Chow says. Although DMEK usually yields better results than DSAEK, the procedure is not appropriate for some people who have had prior glaucoma surgery.
The outer layers, the front part of the cornea, can be transplanted with a deep lamellar anterior keratoplasty. “During this procedure, we replace more than 90 percent of the cornea,” Dr. Chow says. “But we don’t replace the patient’s own inner layer, the endothelial cells, so there is less chance of endothelial graft rejection.”
When the entire cornea has to be replaced—if there is a full-thickness scar or a large perforation—a full-thickness cornea transplant is performed.
Regardless of how many layers are transplanted, the operation is performed in an outpatient setting, typically under light sedation. For endothelial corneal transplants such as DSAEK or DMEK, during which an air or gas bubble is placed within the eye, the patient is asked to lie flat for several hours to days at home. Lying flat with the eyes pointed upward helps to insure that the transplanted tissue remains attached properly.
What are the risks of the procedure?
Overall, using a donated cornea is very safe. Unlike other types of transplants, cornea transplants do not require the blood type of the donor to match the blood type of the recipient. But, like all transplanted tissue, the donated cornea is tested to be sure that it is free of infection or disease and safe to use.
There is a small risk that the patient’s immune system will reject the graft (living tissue that is implanted surgically) or that the graft will fail. The doctor will prescribe steroid eye drops that reduce the risk of rejection.
Infection is also a risk, as it is with any eye surgery. With full-thickness transplants, depending on how the healing process occurs, some patients may end up with significant corneal astigmatism and require glasses or rigid contact lenses for best corrected vision.
What makes Yale Medicine’s approach to cornea transplants unique?
The expert ophthalmologists at Yale Medicine are skilled in advanced and innovative procedures that optimize outcomes for their patients. We have one of only two ophthalmologists in Connecticut who currently perform the DMEK procedure (which has a faster recovery and less graft rejection).
Highly skilled and experienced ophthalmologic surgeons ensure that all of the best options are available to Yale Medicine’s patients. They will provide the best solution based on the patient’s unique circumstances.