Impact of annual dosing with ivermectin on progression of onchocercal visual field loss

Reported are the results of a randomized, double-masked, placebo-controlled trial of annual ivermectin dosing in 34 rural communities, Kaduna State, northern Nigeria, where guinea savanna onchocerciasis is mesoendemic. A total of 939 individuals underwent Friedmann field analysis at the first examination and saw at least 19 spots in at least one eye. Of these, 636 (68%) completed a subsequent Friedmann field analysis 2-3 years later. The adjusted incidence rate ratio for the ivermectin group versus the placebo group was 0.64 (95% confidence interval (CI): 0.42-0.98). There was some evidence that the impact of ivermectin was greatest among those who had received one dose of ivermectin. The majority of the deteriorations occurred in eyes that gave evidence of optic atrophy at the first examination. An analysis restricted to individuals with optic atrophy at baseline indicated a reduction of 45% in the incidence of visual field deterioration in the ivermectin group (95% CI: 8-67%). Previous findings have shown that ivermectin has an impact on the incidence of optic atrophy. Our results indicate, for the first time, that ivermectin has a substantial impact on the progression of visual field loss among those with pre-existing optic atrophy.