Utility and effectiveness of computerised motion sensitivity screening tests in rural onchocercal community survey

BACKGROUND: Non-invasive tool of community diagnosis for onchocercal endemicity needs to be identified and ascertained for their utility and effectivity in order to facilitate the control of onchocerciacis in sub-Saharan Africa OBJECTIVE: To determine the utility and effectiveness of the Wu-Jones Motion Sensitivity Screening Test (MSST) in detecting optic nerve diseases in onchocercal-endemic rural Africa. METHODS: MSST was applied to sampled subjects in the selected communities of Raja in Sudan; Bushenyi in Uganda; Morogoro in Tanzania; and of Ikom, Olamaboro and Gashaka in Nigeria. Basically, six points within the central field of vision were repeatedly tested at 1/3 meter from the screen of a laptop computer in a room darkened. Motion sensitivity was expressed as a percentage of motion detected in the individual eye and this was averaged for the community. RESULTS: A total of 3,858 eyes of 2,072 patients were examined. Seventy-six percent of the subjects completed the test, at an average test time of 120.4 (66.7) seconds. The overall mean motion sensitivity of all eyes tested was 88.49 (17.49%). At a cut-off point of 50%, 6.4% of all subjects tested were subnormal, while at 70% cutoff, 13.3% were subnormal. The highest proportion of 50% cutoff sub-normality was recorded at Morogoro at 12.7%. CONCLUSION: Motion Sensitivity Screening Test was widely accepted and easily administered to the rural and largely illiterate subjects studied. Our data suggest that the proportion of severe field defects by MSST in a community, with cutoff at 33%, best correlates with optic nerve disease prevalence, while proportion of defect from a higher cut-off level at about 50%, best correlates with overall ocular morbidity.