The cornea is the eye’s outermost layer. It is the clear, dome-shaped surface that covers the front of the eye. Because the cornea is smooth and clear like glass and is strong and durable, it helps the eye in two ways.
- First, it shields the rest of the eye from germs, dust, and other harmful matter. Of course, this protective task is shared with the eyelids, the eye socket, tears, and the white part of the eye or sclera.
- Second, the cornea acts as the eye’s outermost lens 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.
When light strikes the cornea, it bends or refracts that incoming light onto the lens. The lens further refocuses that light onto the retina, a layer of light sensing cells lining the back of the eye that is the first step in the translation of light into the perception of images that constitutes our vision. To see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina so that the retina can convert the light rays into impulses sent through the optic nerve to the brain to interpret them as clear images.
This refractive process is similar to a camera. The cornea and lens in the eye act as the camera lens and the retina is similar to the film. If the image is not focused properly, the film (or retina) receives a blurry image. 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.