RED-DOT CARD TEST OF THE PARACENTRAL FIELD AS A SCREENING-TEST FOR OPTIC-NERVE DISEASE IN ONCHOCERCIASIS

A new screening test for optic nerve pathology is described, consistin g of a series of four red targets presented at an angle of 12 degrees in the paracentral field above and below the horizontal meridian. Non- perception and desaturation of the targets are recorded. inter-observe r variability studies found a kappa value = 0.8. A total of 6831 indiv iduals aged greater than or equal to 5 years in communities that were mesoendemic for savanna onchocerciasis in Kaduna State, northern Niger ia, were screened using the test. Of the participants 22% were unable to complete the test; almost two-thirds of these (62%) were aged 5-8 y ears. After exclusion of those visually impaired or blind according to WHO criteria and those unable to complete the test the test showed a sensitivity of 40% and a specificity of 98% for optic nerve disease wh en inability to visualize one or more targets was used as the definiti on of test failure. The sensitivity increased to 54% with a specificit y of 96% when the criterion for failure included desaturation of one o r more targets, These values compare favourably with those for other a vailable screening methods. The test took 1-2 minutes to perform and w as readily accepted by patients and nurses.