[Reproducibility of three-dimensional point by point measurements on the optic nerve head surface using a computerized image analysis system].

The reproducibility of topographic measurements of the optic nerve head was studied using a prototype Humphrey Retinal Analyzer system (Allergan Humphrey SKB, San Leandro, CA). Digital simultaneous stereographic images were obtained using programs in the Analyzer. The analyzer expressed the results in terms of microns of elevation at approximately 300 locations on the optic nerve head surface. At least 3 separate stereoscopic digital images were made of each of 8 eyes of 5 subjects. One randomly selected image of each disc was analyzed twice in order to determine intra-image reproducibility, and topographic analyses of two randomly selected images of each disc were compared to estimate the inter-image variability. We calculated the coefficients of variation (CV) of measurements at the center point of the optic disc. Further, we computed the absolute value of the difference in the degree of elevation among the measured locations on the optic disc and calculated the median and 95 percentile value of that group of approximately 300 differences. The CV, medians, and the 95 percentile values thus obtained for the 8 discs ranged from 0 to 6.1%, from 6 to 20 microns, and from 20 to 69 microns, respectively for intra-image reproducibility. Those for inter-image reproducibility ranged from 1.5 to 59.1%, from 6 to 33 microns, and from 36 to 92 microns, respectively.