Conjunctivitis is swelling (inflammation) or infection of the membrane lining the eyelids (conjunctiva).

The conjunctiva is exposed to bacteria and other irritants. Tears help protect the conjunctiva by washing away bacteria. Tears also contain enzymes and antibodies that kill bacteria.

There are many causes of conjunctivitis. Viruses are the most common cause. Other causes include:

• Allergies (allergic conjunctivitis)
• Bacteria
• Certain diseases
• Chemical exposure
• Chlamydia
• Fungi
• Parasites (rarely)
• Use of contact lenses (especially extended-wear lenses)

"Pink eye" refers to a viral infection of the conjunctiva. These infections are especially contagious among children.

Newborns can be infected by bacteria in the birth canal. This condition is called ophthalmia neonatorum, and it must be treated immediately to preserve eyesight.

See also:

• Allergic conjunctivitis
• Keratoconjunctivitis sicca
• Neonatal conjunctivitis
• Trachoma
• Vernal conjunctivitis

• Blurred vision
• Crusts that form on the eyelid overnight
• Eye pain
• Gritty feeling in the eyes
• Increased tearing
• Itching of the eye
• Redness in the eyes
• Sensitivity to light

• Examination of the eyes
• Swab of conjunctiva for analysis

Treatment of conjunctivitis depends on the cause.

Allergic conjunctivitis may respond to allergy treatment. It may disappear on its own when the allergen that caused it is removed. Cool compresses may help soothe allergic conjunctivitis.

Antibiotic medication, usually eye drops, is effective for bacterial conjunctivitis. Viral conjunctivitis will disappear on its own. Many doctors give a mild antibiotic eyedrop for pink eye to prevent bacterial conjunctivitis.

You can soothe the discomfort of viral or bacterial conjunctivitis by applying warm compresses (clean cloths soaked in warm water) to your closed eyes.

The outcome is usually good with treatment.

Reinfection within a household or school may occur if you don't follow preventive measures.

Call for an appointment with your health care provider if your symptoms last longer than 3 or 4 days.

Good hygiene can help prevent the spread of conjunctivitis:

• Change pillowcases frequently.
• Do not share eye cosmetics.
• Do not share towels or handkerchiefs.
• Handle and clean contact lenses properly.
• Keep hands away from the eye.
• Replace eye cosmetics regularly.
• Wash your hands often.

Wirbelauer C. Management of the red eye for the primary care. American Journal of Medicine. 2006;119:302-306.

Mueller JB, McStay CM. Ocular infection and inflammation. Emerg Med Clin North Am. 2008.26:57-72.

Rubenstein JB, Jick SL. Disorders of the conjunctiva and limbus. In: Yanoff M, Duker JS, Augsburger JJ, et al, eds. Ophthalmology. 2nd ed. Philadelphia, Pa: Mosby Elsevier; 2004: chap 55.