EARLY DIAGNOSIS OF ETHAMBUTOL SIDE-EFFECTS ON THE OPTIC-NERVE USING ASPECIAL COLOR TEST

Chart '65' in Stilling's pseudoisochromatic plates is the most sensiti ve test for ethambutol-induced side effects on the optic nerve. Since ethambutol intoxication accounts for a color-contrast defect at postre ceptoral level, the size of the retinal image of the test figure plays an important role. Therefore, by measuring the distance in which the test figure can be recog nized, very accurate information about the co lor vision defect caused by ethambutol is available. The plate is show n in a viewing box illuminated by two standardized lamps. Variations o f the optotype were introduced by cutting the plate vertically. In thi s way, not only 65, but also 56, 59, and 95 could be shown. Thus, vari ous colored optotypes with identical demands on color vision are at ou r disposal. Preliminary results from our study of more than 100 patien ts at the Heidelberg Tuberculosis Clinic show that about 95% of all pa tients tolerate the therapeutically necessary ethambutol dosage. The r emaining 5% are ethambutol-at-risk patients who can be identified by o ur new color test.