The conjunctiva is the membrane that lines the eyelid and loops back to cover the sclera (the tough white fiber layer covering the eye), right up to the edge of the cornea (see Biology of the Eyes: Structure and Function of the Eyes). The conjunctiva helps protect the eye by keeping small foreign objects and infection-causing microorganisms out and by contributing to the maintenance of the tear film.
The most common disorder of the conjunctiva is inflammation (conjunctivitis). There are many causes of inflammation, including infections by bacteria (including chlamydia), viruses, or fungi; allergic reactions; chemicals or foreign bodies in the eye; and overexposure to sunlight. Conjunctivitis tends to be relatively short-lived, although it sometimes lasts for months or years. Long-standing conjunctivitis is often caused by chronic irritation of the eye that occurs when an eyelid is turned outward (ectropion) or inward (entropion), by some eye drops, or by chronic dryness. Whatever the cause, people with conjunctivitis typically have similar symptoms, such as redness, itching or irritation, discharge, and, sometimes, slightly blurred vision.
The sclera is the tough, white, outer coat of the eyeball. The sclera provides the eyeball with structural strength and protects against penetration and rupture. Rarely, the sclera becomes inflamed (scleritis).
Last full review/revision November 2012 by Melvin I. Roat, MD, FACS