The outer covering of the eyeball consists of a relatively tough, white layer called the sclera. Light enters the eye through the cornea, the clear, curved layer in front of the iris and pupil. Near the front of the eye, in the area protected by the eyelids, the sclera is covered by a thin, transparent membrane, which runs to the edge of the cornea. The conjunctiva also covers the moist back surface of the eyelids and eyeballs.
