Conjunctivitis. Abstract illustration of an eye with conjunctivitis, shown inside the iris of a normal eye. Conjunctivitis is inflammation of the conjunctiva - the membrane that covers the surface of the eye and lines the eyelids. It can be caused by infection with bacteria and viruses, or can be triggered by allergy. Symptoms include redness, irritation, itching, and a discharge, which may be clear or contain pus. One of the most common medical complaints, conjunctivitis accounts for over 2% of visits to the doctor. Treatment depends on the cause and severity.