Cornea

The transparent thin-walled dome that forms the front of the eyeball. The cornea is joined at its circumference to the sclera (white of the eye); the black pupil and the coloured iris are visible beneath it. The main functions of the cornea are to help focus light-rays on to the retina at the back of the eye and to protect the front of the eye. It is kept moist by tears produced by the lacrimal gland and the mucus- and fluid-secreting cells in the eyelids and conjunctiva.