REGIONAL TEST-RETEST VARIABILITY OF CONFOCAL SCANNING LASER TOMOGRAPHY

PURPOSE: To determine the regional differences in the test-retest vari ability of topographic measurements of the optic nerve head obtained w ith a confocal scanning laser retina tomograph. METHODS: Three 10-degr ee topographic images centered on the optic disk of 20 individuals (20 eyes), five normal subjects, seven glaucoma suspects, and eight glauc oma patients, were acquired and averaged. For each eye, the standard d eviation of the mean height at each pixel was calculated from the thre e images and displayed as a gray scale map, which represents regional test-retest variability. The standard deviation of the mean height of the eight surrounding pixels of each pixel was calculated and plotted as a gray scale map, which represents regional steepness. RESULTS: The variability maps and steepness maps showed close correspondence in al l eyes. Regions of high steepness had high variability (r = .31; P < . 001). The average variability in relatively flat areas (sixth to 15th percentiles for steepness) was 19 mu m, whereas steeper areas (81st to 95th percentiles for steepness) had an average variability of 37 mu m The overall mean variability was 28 +/- 7 mu m. CONCLUSIONS: The regi onal variability of topographic measurements made with the confocal sc anning laser tomograph correlates with the steepness of the correspond ing region and is highest at the edge of the optic disk cup and along vessels. Because of their high test-retest variability, these steep ar eas may not be the best locations to follow up patients for progressiv e glaucomatous damage.