Differences in optic disc topography between black and white normal subjects

Purpose To determine if differences in optic disc topography exist between blacks and whites independent of racial differences in the area of the scleral canal. Design Cross-sectional observational study. Participants A cohort of 146 eyes from black subjects and 97 eyes from white subjects without detectable ocular disease. Methods Reliable bilateral images were obtained using a retinal topographer. Mean values for all topographic parameters were compared both unadjusted and adjusted for differences in optic disc area and/or reference plane height. Comparisons of group differences for parameters and linear discriminant functions were adjusted for interocular dependence and multiple comparisons. Results Blacks had a significantly greater optic disc area (mean disc area in right eye: black subjects, 2.14 mm 2 ; white subjects, 1.96 mm 2 [ P = 0.02]; mean disc area in left eye: black subjects, 2.18 mm 2 ; white subjects, 2.02 mm 2 [ P = 0.04]). Most racial differences in optic disc parameters were not significant after adjustment for differences in optic disc area and reference plane height. However, eyes of black subjects demonstrated a deeper maximum cup depth than those of whites ( P = 0.004), independent of differences in disc area and reference plane height. The values of linear discriminant functions did not differ significantly between racial groups, and the Moorfield classification correctly identified a similar proportion of subjects as normal in each racial group. Conclusions Most of the normal variation in optic disc topography between blacks and whites seen with a retinal topographer is due to either differences in disc area or differences in reference plane height. However, small residual differences remain in cup depth independent of these parameters. These racial differences in optic disc structure should be considered in the statistical judgment of disease status based on these parameters. The Moorfield classification, which takes disc area into account, performed with similar specificity in each racial group.