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 (the clear layer in front of the iris and pupil—see Structure and Function of the Eyes Structure and Function of the Eyes The structures and functions of the eyes are complex. Each eye constantly adjusts the amount of light it lets in, focuses on objects near and far, and produces continuous images that are instantly... read more ). 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 Chlamydia trachomatis Chlamydia are bacteria that cause disease in humans, including sexually transmitted infections (STIs), and infections of the eyes and respiratory tract. Three species of Chlamydia... read more ), viruses, or fungi (see Infectious Conjunctivitis Infectious Conjunctivitis Infectious conjunctivitis is inflammation of the conjunctiva usually caused by viruses or bacteria. Bacteria and viruses can infect the conjunctiva. Redness and tearing or discharge are common... read more
)Chemicals or foreign bodies in the eye
Overexposure to sunlight
Conjunctivitis tends to be relatively short-lived, but some kinds last for months or years. Long-standing conjunctivitis is often caused by chronic allergies, chronic infections (trachoma Trachoma Trachoma is a prolonged infection of the conjunctiva caused by the bacterium Chlamydia trachomatis. Chlamydia trachomatis can infect the eye, usually in children who live in lesser-developed... read more 
), and chronic irritation of the eye that occurs when an eyelid is turned outward (ectropion Entropion and Ectropion Entropion is a condition in which the eyelid is turned inward (inverted), causing the eyelashes to rub against the eyeball. Ectropion is a condition in which the eyelid is turned outward (everted)... read more 
) or inward (entropion Entropion and Ectropion Entropion is a condition in which the eyelid is turned inward (inverted), causing the eyelashes to rub against the eyeball. Ectropion is a condition in which the eyelid is turned outward (everted)... read more ), by some eye drops, or by chronic dryness. Whatever the cause, people with conjunctivitis typically have similar symptoms, such as redness and discharge. Some types of conjunctivitis also cause itching or irritation.
The sclera is the tough, white, outer layer of the eyeball. The sclera provides the eyeball with structural strength and protects against penetration and rupture. Rarely, the sclera becomes inflamed (scleritis Scleritis Scleritis is severe, destructive inflammation of the sclera (the tough, white, fiber layer covering the eye) that may threaten vision. Scleritis sometimes occurs in people who have a bodywide... read more ).
The episclera is a thin tissue layer overlying the sclera. The episclera contains tiny blood vessels that supply nutrients to the sclera. Sometimes the episclera becomes inflamed (episcleritis Episcleritis Episcleritis is inflammation of the tissue lying between the sclera (the tough, white, fiber layer covering the eye) and the conjunctiva (the membrane that lines the eyelid and covers the white... read more 
).
An Inside Look at the Eye
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