TEST-RETEST VARIABILITY OF TOPOGRAPHIC MEASUREMENTS WITH CONFOCAL SCANNING LASER TOMOGRAPHY IN PATIENTS WITH GLAUCOMA AND CONTROL SUBJECTS

Using confocal scanning laser tomography, we studied the test-retest v ariability of topographic measurements of the optic nerve head and par apapillary retina in 30 patients with glaucoma and 30 normal control s ubjects. We obtained three independent images, separated by between on e and six hours, centered on the optic nerve head. We condensed each o riginal 256 x 256-pixel image to a 64 x 64-pixel image, thereby allowi ng a realistic estimate of the empiric 90% confidence interval of test -retest variability at each condensed pixel. Confidence interval maps generated for each subject showed highest measurement variability alon g the cup border and blood vessels. The mean standard deviation equiva lents of test-retest variability in the patients and controls were 31. 20 and 25.94 mu m respectively. These differences were statistically s ignificant (P = .010). Variability increased with age (P < .001), When the analysis was repeated for discrete parapapillary areas, the group differences were not statistically significant (P = .100).