Oestrus ovis ophthalmomyiasis externa.

Oestrus ovis, the sheep nasal botfly, is the most common cause of ophthalmomyiasis externa in North America. In the United States, most cases occur on Catalina Island. The symptoms of acute infestation with this organism resemble those of catarrhal conjunctivitis and the condition is considered to be self-limiting. Treatment consists of careful removal of the organisms and topical administration of corticosteroid and antibiotic drugs to relieve the symptoms and prevent bacterial contamination. We recently examined a 17-year-old woman who had visited Catalina Island and later developed acute O. ovis ophthalmomyiasis externa. To determine the incidence of chronic complications, we performed ophthalmic examinations on 15 Catalina Island residents who had had documented O. ovis ophthalmomyiasis externa before 1981. We found no evidence of persistent infestation or intraocular penetration by these organisms.