ABSTRACT: Signs and symptoms of a full-blown ocular allergic reaction include deep red vessels in the conjunctiva, itching, and swelling of the conjunctiva and eyelids. Ocular allergy can resemble nonallergic conditions, including drug-induced conjunctivitis, blepharitis, and viral or bacterial infection. A history of itching confirms a diagnosis of allergy. To distinguish allergic conjunctivitis from more serious allergic ocular diseases, inspect the lids and cornea for papillae on the upper tarsal surface, which occur in giant papillary conjunctivitis and vernal or atopic keratoconjunctivitis. Local treatment of allergic conjunctivitis consists of over-the-counter and prescription antihistamines, with or without vasoconstrictors or mast cell stabilizers. Combination mast cell stabilizer/ antihistamine topical ophthalmic agents-the newest class of medication-are considered the most effective treatment of allergic conjunctivitis. Oral antihistamines are not indicated unless a patient has an allergic condition, such as rhinitis, dermatitis, or asthma.