Variability of optic disk topographic measurements obtained with the Rodenstock Optic Nerve Head Analyzer was determined by obtaining three separate images on one eye of ten normal subjects and nine subjects without glaucoma. Marking of the disk margin was performed in a random and masked fashion on each image three times by three independent observers. The overall variabilities of the measurements of the subjects with glaucoma were not statistically different from those of the normal subjects. Overall variability was about 0.2 mm2 for total disk area, 0.08 for cup/disk ratio, 0.2 mm2 for disk rim area, and 0.07 mm3 for cup volume. The largest component of the variability was the result of acquisition of separate images of the optic disk at different times. Observer inconsistency in marking the disk edge was relatively small. Based on the expected amount of random variability of the measurements, we proposed criteria for detecting significant change in the optic disk over time.
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