A comparison of structural measurements using 2 stratus optical coherence tomography instruments

PURPOSE: To compare measures of peripapillary retinal nerve fiber layer (RNFL) thickness, optic disc topography, and central foveal thickness generated using 2 different Stratus optical coherence tomography (OCT) instruments. METHODS: Ten normal subjects and 10 glaucoma subjects were included. One randomly selected eye per subject was scanned consecutively using a fast RNFL thickness protocol, fast macular thickness map, and fast optic disc protocol by 2 experienced operators on 2 instruments. The order of the machines and operators were randomized. The output power of each machine was measured using an optical power meter. For each OCT measurement 2 factor fixed effects analyses of variance were performed and a restricted maximum likelihood variance component analysis of the proportion of variance due to subject, operator, and machine was calculated. RESULTS: Significant differences (P≤0.003) between OCT instruments were observed in average, superior, and inferior RNFL thickness and central foveal thickness values among normal eyes; and average and superior RNFL thickness and cup/disc area ratio values among glaucomatous eyes. Overall, the intermachine variability (0.0% to 16.4%) was larger than the interoperator variability (0.0% to 2.4%) for all OCT measurements. In the glaucoma group the variability due to machine differences was 2.6 μm for the average RNFL thickness, 5.7 μm for the superior RNFL thickness, 0 μm for the inferior RNFL thickness, 0.03 μm for the cup/disc area ratio, 0.01 μm for the cup/disc vertical ratio, and 2.8 μm for the average foveal thickness. CONCLUSIONS: Measurements of RNFL thickness, optic disc topography, and central foveal thickness significantly differ between OCT instruments.