The causes and profile of visual loss in an onchocerciasis-endemic forest-savanna zone in Nigeria

Abstract

In an onchocerciasis-endemic forest-savanna mosaic zone of southeastern Nigeria, blindness was found in 5.4% of 1,217 people who voluntarily attended for examination from a population of 14,000. Apart from cataract, the most important causes of blindness in the area were eye diseases that are known to be associated with onchocerciasis. Refractive error, although a non-onchocerciasis-related eye defect, was the number one cause of visual loss found in the study. The causes of blindness in our examined population are similar to what is found in onchocerciasis-endemic areas of the savanna zone and dissimilar from those found in the forest zone. In this forest-savanna mosaic zone, the prevalence of onchocerciasis was higher in the respondents with poor vision than in those with adequate vision. Similarly, low vision was found to be more common in people with high microfilarial loads, but people with high loads also tended to be older than those with moderate or low microfilarial loads, which might suggest that low vision was only a function of age. Nonetheless, analysis of our data shows evidence of an association between low vision and microfilarial load in adults aged 60 years and above. It is concluded that onchocerciasis in the forest-savanna mosaic zone of Nigeria has the features until recently associated only with savanna onchocerciasis, and that this should be taken into consideration in planning and executing onchocerciasis control programs in the area.