What is the cornea?
The cornea is the clear, dome-shaped outermost layer of the eye. It may not look like much, but it performs a very important function: it bends incoming light rays in a very precise manner, so that they focus directly on the retina (the lining of the back of the eye), allowing you to see clearly.
In order for the cornea to focus these light rays just right, it must be crystal clear, perfectly smooth, and have exactly the right shape. If injury or disease causes the cornea to become cloudy, scarred, irregularly shaped, or otherwise damaged, vision problems are the result. These problems may be mild or severe, depending on the extent and location of the damage.
Why might a transplant be needed?
Some corneal problems can be treated with medications, eyeglasses, or contact lenses, but for some the damage is irreparable. In these cases, the only way to restore sight is by replacing the damaged cornea with one from a donor. Possible reasons for needing a corneal transplant include:
- Complications from eye surgery such as LASIK or cataract surgery
- Keratoconus (a disorder in which the cornea becomes thin and the eye bulges into a cone-shape)
- Hereditary corneal disorders, such as Fuch's cornea
- Scarring, which can be caused by an injury or by an infection, such as eye herpes or acanthamoeba keratitis
- Cloudiness, which can be the result of an injury or various eye diseases
How is the transplant done?
Corneal transplant is one of the most common, and most successful, transplant procedures performed. It is estimated that, in the United States, over 40,000 of these transplants are done each year.
With other organ transplants, you could be waiting for years on a list, but the waiting period for a donor cornea is very short, typically just one to two weeks in the U.S. This is thanks to a network of eye banks that store donor tissue. As with blood and other donor material, corneas are inspected and tested for damage and disease before they are given to a recipient.
Corneal transplant is an outpatient procedure, and can be performed under local or general anesthesia. There are a number of factors that will determine whether you will be asleep or awake for the procedure, including your general health, age, and which you would prefer. If local anesthesia is used, an injection will relax the muscles in your eyes to prevent blinking and movement during the procedure, and eye drops will be applied to the eye as a numbing agent. Your eyelids will be held open with a lid speculum, and you may also be given a sedative to help you relax.
Most commonly, the entire thickness of the cornea is replaced (called a penetrating keratoplasty). The surgeon will inspect your eye, to measure the amount of tissue needed. An instrument called a trephine, which is like a circular cookie-cutter, is used to cut out a very precise button of tissue from your cornea. An identical piece of tissue is cut from the donor cornea, and placed into this space. Very fine thread is used to suture the donor tissue in place.
In some cases, only certain layers of the cornea need to be replaced. This can be a deep lamellar transplant, in which the innermost layer of the cornea is replaced with donor tissue, or a surface lamellar transplant, in which the outermost layers are removed and a donor graft put in place.
Corneal transplant surgery typically takes one to two hours. After surgery is completed, a protective plastic shield will be placed over your eye.
The recovery process
As with any transplant, the cornea must be watched carefully for signs of rejection, which include redness, pain, vision problems, and sensitivity to light. Rejection may occur in as many as 21% of recipients. Oftentimes, this can be successfully treated, though in some cases the graft fails and another transplant is required. Rejection may occur as late as 5 years after transplantation.
Healing time after a corneal transplant can be a year or more. Immediately following surgery, the grafted tissue will be swollen and thicker than the surrounding cornea, causing blurry vision. Within three to seven days after surgery, your vision may be improved enough for you to resume normal activities, including work, except for certain tasks such as heavy lifting and strenuous exercise. Eye protection, such as eyeglasses, should be worn at all times.
The stitches may need to be adjusted during the healing process. They will remain in the eye for three to seventeen months after surgery.
The curve of the transplanted cornea will not exactly match your original, so vision correction, such as glasses or contact lenses, will be needed after surgery. Rigid gas permeable (RGP) contact lenses may be especially helpful in correcting vision problems caused by corneal abnormalities.
It can take a few months to a year for your vision to stabilize into a permanent prescription, so you may not want to get purchase corrective lenses immediately following surgery. Once the healing process is complete and the sutures removed, surgical vision correction, such as LASIK, may be a good alternative to lenses for some patients.
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