The conjunctiva secretes a watery fluid (mucus) that helps lubricate the eyeball and keep it moist.

What keeps the eye moist?

Small glands at the edge of the upper and lower eyelids secrete an oily substance that contributes to the tear film and keeps tears from evaporating. Tears keep the surface of the eye moist. Without such moisture, the normally transparent cornea can become dried, injured, infected, and opaque.

What is a good lubricant for eyes?