The cornea is the transparent, dome-shaped, outermost layer that covers the iris and pupil in the front of the eye. Corneal tissue consists of five basic layers: epithelium, Bowman’s layer, stroma, Descemet’s membrane and endothelium. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection.
The cornea, one of the protective layers of the eye, serves two functions:
First, along with the eyelid, eye socket, and sclera (white part of the eye), and the tear film, the cornea shields the eye from dust, germs, and other harmful matter.
Second, as the eye’s outermost lens, it is the entry point for light into the eye. When light strikes the cornea, it bends, or refracts, the incoming light onto the lens. The lens further refocuses the light onto the retina, a layer of light-sensing cells lining the back of the eye.
To see clearly, the cornea and lens must focus the light rays precisely on the retina. This refractive process is similar to the way a camera takes a picture. The cornea and lens in the eye act as would a camera’s lens. The retina approximates the film. If the cornea is unable to focus the light properly, then the retina receives a blurry image.
Corneal transplants are one of medicine’s most successful transplant operations. The procedure involves removing the cornea from the donor eye with a special instrument resembling a small cake cutter. The same method is used to remove the damaged cornea from the patient’s eye. The surgeon then stitches the new cornea into place.
For many individuals, a corneal transplant may be the only hope for restored vision, and may be necessary when the cornea is cloudy or damaged due to disease, injury, accident, or hereditary conditions. In these situations, the cornea must be removed and replaced with healthy donor tissue. The procedure is successful in 90 percent of cases, restoring sight and, in some cases, even providing sight for the first time.
Reasons include: