Influence of optic disc size on neuroretinal rim shape in healthy eyes

Purpose: To evaluate the influence of optic disc size on segmental neuroret inal rim area in healthy eyes. Patients and Methods: The study included 193 eyes of 193 healthy patients w ith physiologic disc cupping. On 15 degrees color stereophotographic optic disc diapositives, optic disc area and neuroretinal rim area were morphomet rically determined in 36 radial optic disc segments each measuring 10 degre es. Results: The correlations of segmental rim area to disc area were significa ntly strongest (P < 0.01) and the regression lines were steepest in the inf erior disc region, and the values were lowest in the temporal disc region. Complementary to the rim data, the correlations of segmental cup area to di sc area were significantly strongest (P < 0.01) and the regression lines we re steepest in the temporal disc region, and the values were lowest in the inferior disc region. In comparison with neuroretinal rim area, cup area wa s significantly (P < 0.01) more strongly correlated with disc area and the regression line was steeper in the whole optic disc and in each disc segmen t. The regional distribution of the widest rim part and smallest rim part w as independent of disc size. Conclusions: The increase of rim area and cup area with increasing disc siz e differs between various disc regions. Because cup area increases more tha n rim area with increasing disc size, correction for disc size may be more important for segmental cup area than for segmental rim area. The rim shape with respect to the location of the smallest or broadest rim part is indep endent of disc size.