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.