The evolution of ocular onchocerciasis in the Volta River Basin Area over a period of five years of vector control.

The results of an ophthalmological evaluation conducted in seven West African savannah villages before and after 5 years of vector control, were analysed to determine the effect of an interrupted or greatly reduced transmission of Onchocerca volvulus on the evolution of ocular onchocerciasis. Cross-sectional data showed a significant reduction of the prevalence of ocular onchocerciasis in five of the villages, and the rates of irreversible ocular lesions and blindness were generally lower after 5 years of vector control. A longitudinal study of a defined population showed that the ocular status of most patients with ocular onchocerciasis remained stable or improved over the 5 year period, particularly in lightly infected cases. The evolution of ocular onchocerciasis showed a deterioration in a minor proportion, restricted to cases of already existing severe lesions, resulting in blindness. A comparison of ophthalmic data from adjacent areas without vector control, indicates that a five year period of vector control may reduce the risk of developing eye lesions or blindness due to onchocerciasis by 50%.