Neuroretinal rim area in normal eyes: a study on a randomized group of 30 subjects

This study was undertaken in order to evaluate the range of the neuroretinal rim area in a normal sample and the repeatability of manual photogrammetric measurements. Thirty randomly chosen eyes from 30 subjects without ocular disease were examined: the mean disc area (2.20 +/- SD 0.58 mm2), the mean cup area (0.36 +/- 0.29 mm2) and the mean rim area (1.83 +/- 0.37 mm2) were evaluated. All the measurements were performed by two independent observers and were corrected to the actual size by measuring refraction and axial length of each eye. A linear correlation among disc areas (r = 0.71), cup areas (r = 0.93) and rim areas (r = 0.74) between the two observers was found. Furthermore, a highly significant correlation between disc area and rim area was observed (r = 0.90) together with a correlation between the disc and cup area (r = 0.82). A correlation between disc area and axial length was finally found (r = 0.59). The neuroretinal rim area has been expressed as a percentage of the total disc area. Percent values (+/- SD) were clustered around a mean of 84.83 +/- 8.8%. Despite their high degree of repeatability, our data are slightly different from those previously reported by other authors.