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Cornea
Layers
The cornea has five layers, each with its own function. The outside layer of the cornea, the
epithelium, is protective like thin, fine skin. The cornea is extremely sensitive. It has
the highest concentration of pain fibers in any part of the body. The pain fibers are just
below the epithelium. Thus, the smallest particle of dirt can feel like a cinder, and a
small scratch on the surface of the epithelium can be painful. Lack of oxygen from improper
use of a contact lens can cause corneal swelling and severe pain. Fortunately, this outer
layer heals rapidly from most minor injuries. Most injuries that involve only the outer
layer will heal without scarring.
The normal cornea is the clear front window of the eye. The colored iris and black
pupil are seen through the cornea.
The innermost layer, called the endothelium, is one cell layer in thickness. Its
function is to keep the cornea clear by continuously pumping fluid out of the cornea. It
does not reproduce cells. The cells with which you are born are the only cells you will have
during your lifetime. Any cells that are damaged cannot be replaced. As we get older the
number of endothelial cells decreases slightly. If the number decreases too much, the cornea
begins to swell with fluid and becomes hazy. In the early stages of swelling, medication can
help, but when the cornea becomes increasingly swollen, a corneal transplant is the only
solution. This swelling of the cornea with fluid is called Òcorneal edema.Ó This swelling
acts like water droplets behind your watch crystal that fog the view of your watch dial.
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