What is the cornea?

The cornea is the transparent tissue that covers the front of the eye (see diagram). An easy way to locate the cornea is simply to look at your eye in the mirror. You will notice a clear surface covering the iris (the colored part of the eye) and pupil. This is the cornea.

What is the function of the cornea?

Because the cornea is as smooth and clear as glass but as strong and durable as plastic, it helps the eye in two ways:

The cornea provides a physical barrier that shields the inside of the eye from germs, dust, and other harmful matter. It shares this protective task with the sclera (the white of the eye).

It acts as the eye's outermost lens. When light strikes the cornea, it bends--or refracts--the incoming light onto the crystalline lens. The lens then focuses the light onto the retina, the paper-thin tissue at the back of the eye that starts the translation of light into vision.

Although much thinner than the lens, the cornea provides about 65 percent of the eye's power to bend light. Most of this power resides in the center of the cornea, which is rounder and thinner than the outer part of the tissue and is thus better suited to bend lightwaves.

How important is the cornea to good vision?

The cornea is essential to good vision. As the eye's outermost tissue, the cornea functions like a window that controls the entry of light into the eye. For example, the cornea filters out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the crystalline lens and the retina would be highly susceptible to injury from UV radiation.