The clear covering of the eyeball is called the cornea. Surgery is performed on the cornea for two main reasons. One is to remove scarring and clouding that interfere with vision. The other is to change the curve of the cornea to correct vision problems. These problems include nearsightedness and farsightedness. Operations on the cornea can be performed with traditional surgical tools or laser surgery can be used.
Who is a candidate for the procedure?
The best candidates for this type of surgery are people with corneal conditions whose vision can't be corrected by wearing glasses or contact lenses. Many people also choose to have corneal surgery for convenience and for cosmetic reasons.
How is the procedure performed?
Several procedures can be performed on the cornea to restore its clarity and allow more light to pass through. Common procedures include the following:
corneal transplant, in which a person's cloudy, diseased cornea is replaced with a cornea from a donor eye
removal of a membrane-like growth on the surface of the cornea called a pterygium
repair of corneal injuries
a scraping of the surface layers of the cornea that have become rough or cloudy to allow normal tissue to grow in its place
A procedure called a conjunctival flap is done when the cornea is diseased and painful. It can also be done when there is danger of the cornea tearing because it is too thin. The mucous membrane that covers the white portion of the eye, called the conjunctiva, is brought over the cornea and stitched in front of it. This provides comfort and protection for the eye. However, the eye will no longer be able to see.
In the last decade, procedures have been developed to correct nearsightedness, farsightedness, and astigmatism. These are termed refractory surgery. One of the first of the procedures was radial keratotomy, or RK. This operation consists of spoke-like cuts in the edges of the cornea. The cuts do not extend over the area covering the pupil. The cuts allow the edges of the cornea to weaken and bow. This causes the area of the cornea over the pupil to flatten and decreases the person's nearsightedness. While this operation is still performed today, it has been almost completely replaced in the United States by a procedure called LASIK.
LASIK, or laser in situ keratomileusis, is usually done on both eyes at once. It can be used to correct farsightedness and nearsightedness with or without astigmatism. In this technique, a thin flap of the cornea is lifted. Then a laser is used to dissolve very thin layers of corneal tissue under the flap and create a flatter surface over the pupil. After the laser treatment, the flap is repositioned.
A procedure to correct farsightedness with astigmatism should receive FDA approval soon. Other methods for reshaping the cornea are also under investigation. One of these involves the use of a peripheral corneal ring. Also, a technique for implanting an artificial lens in the eye to correct vision problems shows promise as an alternative to LASIK.