Cornea

The cornea is the curved, transparent layer that covers the front part of the eye. It refracts light and helps the eye to focus, though unlike the lens, the curvature of the cornea cannot be adjusted to tune this focus.

The cornea consists of several layers. First is a thin epithelial layer; these cells are fast-growing and easily regenerated, and are kept moist by the tears. Beneath this is a tough layer called Boman's membrane that protects the cornea. Underneath this is the stroma, a much thicker layer of transparent fibers. The stroma is responsible for most of the focusing; if it is damaged the cornea can lose its transparency and cause problems in vision.