While symptoms can be very distressing, patients with conjunctivitis general maintain good vision and recover completely without permanent sequelae. The great majority of cases of conjunctivitis are infectious or allergic in origin. Seen with increasing frequency are external eye diseases related to contact lens wear or prolonged use of ophthalmic medications. The various forms of conjunctivitis are often not associated with pathognomonic features. A thorough history and ophthalmic examination often permit a presumptive diagnosis and initiation of empiric therapy. For example, a chronic bilateral conjunctivitis, characterized by itching and papillary hypertrophy, suggests an ocular allergy, most frequently the result of exposure to airborne allergens. However, a number of causes, including infections and hypersensitivity reactions, have the potential to threaten vision or produce marked conjunctival scarring which must be identified by the use of appropriate laboratory techniques, followed by specific therapy. Most bacterial and viral conjunctivitis are self-limited, but antimicrobial therapy for the former is advocated to shorten the course, improve patient comfort, prevent recurrence, avoid complications and limit spread to other individuals.