How the cornea works
The cornea is the clear covering of the front of the eye which bends (or refracts) light rays as they enter the eye. For clear vision to occur, the cornea must have the proper shape and power to focus incoming light rays precisely on the retina at the back of the eye. If the cornea is too steep, too flat or irregular in shape, it cannot bend light at the angle needed to focus on the retina. As a result, eyeglasses or contact lenses may be needed to refract the incoming light rays at the angle needed for clear vision.