A randomized, double-blind, controlled trial of the effects of ivermectin at normal and high doses, given annually or three-monthly, against Onchocerca volvulus: ophthalmological results

A three-year randomized, controlled, double-blind trial was conducted in Cameroon to determine whether ivermectin, given at three-monthly intervals and/or at high doses (800 μg/kg), had a greater effect on adult Onchocerca volvulus than standard doses (150 μg/kg annually). As several patients complained of transitory subjective visual problems after treatment, some of them being of an unexpected type, we organized two series of detailed ophthalmological examinations to evaluate whether they were associated with ocular lesions. Analysis showed that these complaints were significantly more frequent in the two groups treated with high doses of ivermectin than in the reference group. In the ophthalmological examinations, the only differences recorded between the groups were a lower prevalence and mean number of microfilariae in the anterior chamber in the groups treated three-monthly, and, at the first examination round, a higher prevalence of early lesions of the iris in the group treated at high doses annually. These findings do not allow us to explain the cause of the transitory ocular complaints, nor why they were more frequent in the groups treated at high doses. However, one may conclude that using doses of ivermectin higher than the standard one should be considered with caution.