Conjunctivitis, or pink eye, is an inflammation or infection of the transparent membrane (conjunctiva) that lines the eyelid and part of the eyeball. Inflammation causes small blood vessels in the conjunctiva to become more prominent, which is what causes the pink or red cast to the whites of the eyes. Conjunctivitis can spread from one person to another and affects millions of Americans at any given time.

The most common conjunctivitis symptoms are redness and itchiness in one or both eyes, a gritty feeling in the eyes, tearing and a discharge that forms a crust during sleep.

Conjunctivitis usually does not affect vision and, typically, doesn’t require extensive or emergency treatment. But because pink eye can be highly contagious for as long as two weeks after signs and symptoms begin, it is important to seek diagnosis and treatment early. If the infection is bacterial, the doctor may prescribe antibiotic eye drops or ointment, and it should clear up in several days. The most common form, viral conjunctivitis is associated with colds, and must run its course since it does not respond to antibiotics. Conjunctivitis can also be caused by allergies. This form is not contagious.

Although pink eye often gets better without treatment, it can be accompanied by an inflammation of the cornea, which can affect vision. Extreme cases may require a corneal transplant.