impact of annual dosing with ivermectin on progression of onchocercal visual field loss reported are the results of a randomized doublemasked placebocontrolled 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 23 years later the adjusted incidence rate ratio for the ivermectin group versus the placebo group was 064 95 confidence interval ci 042098 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 867 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 preexisting optic atrophy