Alcaftadine is an antihistamine that reduces the effects of natural chemical histamine in the body. Histamine can produce symptoms such as itchy or watery eyes. Alcaftadine ophthalmic (for the eyes) is used to prevent itching in the eyes caused by allergies. Alcaftadine ophthalmic should not be used to treat eye irritation caused by contact lenses. Alcaftadine ophthalmic may also be used for purposes not listed in this medication guide.