The cornea is a dime-sized clear tissue that is the front of the eyeball. It is the eye’s outermost layer, normally invisible when viewed straight on. The cornea is a clear, dome-shaped surface that covers the front of the eye, much like a watch crystal or “window” of the eye. It helps direct light rays towards the lens for focusing, and allows light to pass through it to reach the back of the eye.
In order for vision to be clear, the cornea must be clean and clear. Corneal disease can cause the cornea to become opaque or cloudy, preventing light from passing through clearly. Corneal scars, scratches, surface roughness, and irregular curvature will distort vision, and are frequently associated with sensitivity to light (photophobia).