We assessed ocular changes after therapy at six and 12 months with ivermectin (150 micrograms/kg of body weight) in a 12-month prospective study of 29 patients with ocular onchocerciasis and 15 patients with onchocerciasis without ocular involvement. The patients lived in a hyperendemic area in Sierra Leone, West Africa, where no vector control was instituted. Five months after initial treatment, the microfilarial load in skin and eyes had decreased significantly (P less than .0000), but 28 of 44 (63%) patients had positive skin-snip test results and nine of 29 (31%) patients with ocular involvement had active ocular disease. Twelve months after initial treatment, 15 of 41 (37%) patients had positive skin-snip test results and eight of 26 (31%) showed active ocular involvement. All patients with persistent ocular disease after therapy showed evidence of active onchocerciasis at that time, which suggests that a dose of ivermectin at six-month intervals is not sufficient for intensely infested patients with severe ocular disease. We developed an ocular involvement score to evaluate the patient's total ocular status and observed a significant relation between the pretreatment severity of ocular involvement and the persistence of active ocular disease after treatment with ivermectin.