The Cornea is the transparent tissue at the front of the eye. The transparency and shape of the cornea is vital for good vision and any alteration in this can result in poor vision or blindness. Although the cornea is clear and seems to lack substance, it is actually a highly organized group of cells and proteins. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor that fills the chamber behind it. The cornea must remain transparent to refract light properly, and the presence of even the tiniest blood vessels can interfere with this process. To see well, all layers of the cornea must be free of any cloudy or opaque areas.
The Key to Your Vision
It helps to shield the rest of the eye from germs, dust, and other harmful matter. The cornea shares this protective task with the eyelids, the eye socket, tears, and the sclera, or white part of the eye.
The cornea acts as the eye's outermost lens. It functions like a window that controls and focuses the entry of light into the eye. The cornea contributes between 65-75 percent of the eye's total focusing power.
The cornea also serves as a filter, screening out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the lens and the retina would be highly susceptible to injury from UV radiation.
A cornea transplant, which replaces damaged tissue on the eye's clear surface, also is referred to as a corneal transplant, keratoplasty, penetrating keratoplasty (PK) or corneal graft.
A graft replaces central corneal tissue, damaged due to disease or injury, with healthy corneal tissue donated from a local eye bank. An unhealthy cornea affects your vision by scattering or distorting light and causing blurry or glary vision. A cornea transplant may be necessary to restore your functional vision.
Cornea transplants are performed routinely. The National Keratoconus Foundation estimates that more than 40,000 cornea transplants are performed in the United States each year.
Are You a Cornea Transplant Candidate?
Your eye doctor may suggest a corneal transplant for reasons varying from diseases to eye injuries, which can include the following:
Scarring from infections, such as eye herpes or fungal keratitis.
Eye diseases such as keratoconus.
Hereditary factors or corneal failure from previous surgeries.
Thinning of the cornea and irregular shape (such as with keratoconus).
Complications from LASIK.
Chemical burns on the cornea or damage from an eye injury.
Excessive swelling (edema) on the cornea.
Corneal transplants are performed in order to protect the eye's inner structures, relieve pain, and improve vision. With these factors in mind, you should consider several important questions before you decide to undergo a corneal transplant:
Does your functional vision impede your job performance or ability to carry out daily activities?
Can your vision be corrected through special contact lens fittings or other less invasive measures?
How will the cost of surgery affect your financial situation if your vision insurance does not cover everything from pre-screening to post-operative consultations?
Are you able to take enough time off from work or school (six months to a year) to recover properly?
All of these questions, in conjunction with thorough discussions and screenings with your eye doctor, must be weighed before you make the final decision to have a corneal transplant.
Cornea Transplant Procedure
Once you and your doctor have decided that a corneal transplant is the best option to restore your functional vision, your name is placed on a list at a local eye bank. The waiting period for a donor eye is generally one to two weeks due to a very sophisticated eye bank system in the United States. Before donor corneas are released for transplant, tissue is checked for clarity. Also, donor eyes supplying transplant tissue are meticulously screened for presence of diseases or other damage to ensure the health and safety of the recipient.
Typically, corneal transplants are performed on an outpatient basis, meaning that you will not need hospitalization. Local or general anesthesia is used, depending on your health, age and whether or not you prefer to be asleep during the procedure.
After the anesthesia has taken effect, the eyelids are held open with a special instrument (lid speculum). Your eye surgeon inspects and measures the affected corneal area in order to determine the size of the transplantation. A round, button-shaped section of tissue is then removed from your diseased or injured cornea. Any additional work, such as cataract removal, is completed. A nearly identical-shaped button from the donor tissue is then sutured into place. Finally, the surgeon will place a plastic shield over your eye to protect it from being inadvertently rubbed or bumped. The surgery takes one to two hours.
Cornea Graft Rejection
Most corneal transplants are successful. Nevertheless, recognizing the warning signs is the best way to prevent corneal transplant rejection. Familiarize yourself with the four main signs by remembering the acronym RSVP:
Extreme Sensitivity to light
Rejection signs may occur as early as one month or as late as five years after surgery. If you have complications with your corneal transplant, your doctor will prescribe medication that can reverse the rejection process. Should your graft fail, the corneal transplant can be repeated, generally with good results. Still, overall rejection rates increase with the number of corneal transplants you have.
Recovering From a Cornea Transplant
The total recovery time for a corneal transplant may be up to a year or longer. Initially, your vision will be blurry and the site of your corneal transplant may be swollen and slightly thicker than the rest of your cornea. As your vision is restored, you will gradually be able to return to your normal daily activities.
For the first several weeks, heavy exercise and lifting are prohibited. However, you should be able to return to work three to seven days after surgery, depending on your job. Steroid eye drops will be prescribed for several months to help your body accept the new corneal graft. You should keep your eye protected at all times by wearing a shield or a pair of eyeglasses so that nothing inadvertently bumps or enters your eye.
Sight After a Cornea Transplant
Your vision will continue to improve up to one year following your surgery. But you will need vision correction (glasses or contact lenses) for nearsightedness and astigmatism, because the curve of the corneal transplant cannot match exactly the curve of your existing cornea. Because your vision will fluctuate during the first three months following your surgery, it is typical to wait for that time period or until all of your sutures have been removed to fill an eyeglass prescription and be fitted for contact lenses. After healing is complete and stitches are removed, it is possible to undergo laser vision correction (LASIK or PRK) to improve the prescription and enhance ability to see without glasses or contact lenses.
Rigid gas permeable contact lenses, also known as RGP lenses, provide the best vision correction for corneal transplant patients due to the irregularity of the cornea after transplant. However, soft contact lenses often are an option. Finding a contact lens that offers good oxygen permeability will minimize corneal swelling.