Study of the correlation between average values of optic disc parameters and their measurement variability using stereovideographic digital analysis.

Purpose of our study was to find whether there is a correlation between average values of optic nerve head parameters and their coefficient of variation for repeated measurements. Disc stereo video images were taken with Topcon Imagenet (IS100) and analyzed with the Optic Disc Analysis program. Eleven normal and 9 glaucomatous eyes were selected. A significant correlation was found for horizontal cup/disc ratio (r = -0.037, p = 0.037) and disc area (r = 0.776, p = 0.027) in intra-observer intra-image repeated measurements. Vertical, horizontal and average cup/disc ratios (r = -0.81, r = -0.74, r = -0.78 p < 0.05) showed a significant correlation for intra-observer inter-image repeated measurements. For inter-observer intra-image measurements, a significant correlation was present for average cup/disc ratio (r = -0.64, p = 0.043). Our data show that bidimensional semiquantitative parameters in use for optic nerve head assessment, analyzed by computerized stereovideography, have an intrinsic measurement variability. The variability is significantly related to the value of the measured parameter only when their reference points are determined manually by the operator.