The effects of multiple doses of ivermectin on ocular onchocerciasis - A six-year follow-up

Background: Ivermectin has been shown to be a safe treatment for onchocerciasis and is now being distributed through mass treatment programs. Previous studies of up to 3 years of treatment have demonstrated that ivermectin improves anterior segment lesions and reduces the incidence of optic atrophy. The benefit of multiple doses of ivermectin on visual acuity and chorioretinitis has yet to be shown. Methods: A community-based, double-blind, randomized, controlled trial of ivermectin was started in Bo, Sierra Leone, in 1987. Two cohorts are reported in this study: (1) 214 subjects had received four 6-month doses of ivermectin followed by up to six additional 6-month treatments. The second cohort, with 185 subjects, had received four 6-month doses of placebo followed by up to four annual doses of ivermectin. All subjects received a full ophthalmic examination in 1989 and again in 1994. For both cohorts, there was an 18-month gap between the fifth and sixth rounds of treatment. Results: There was no significant difference in the prevalences of any ocular lesion nor of visual acuity categories between the cohorts at the second examination. Comparisons of the prevalences of anterior segment lesions for both cohorts combined between the first and second examinations show highly significant improvement (P < 0.001) for all lesions. Posterior segment lesions show a more variable pattern, with chorioretinitis showing highly significant deterioration (P < 0.001) and the emergence of new lesions in both groups. Conclusion: The authors conclude that annual treatment with ivermectin is effective in controlling ocular onchocerciasis apart from chorioretinal lesions and that a 6-month treatment gives no additional benefit.