Measurement differences between platforms were statistically significant; however, the clinical significance of this difference is less clear. With the exception of the Bioptigen SDOIS, the SDOCT systems evaluated in this study had low variability from a clinical standpoint, albeit statistically significant. Lateral scaling variability was 0.3 to 2% between platforms, which represents a range of 15 to 106 μm in width difference between images (based on nominal 6-mm scans divided by sampling density of 512 A-scans). Axial measurements performed in this study suggest that variability across all platforms was 1.1 to 17% between platforms, equivalent to a difference of 5 to 45 μm based on the nominal axial resolution of these SDOCT platforms. Excluding the axial measurements from the Bioptigen SDOIS, which were consistently smaller than all other platforms, the mean difference decreased to ( or 8 μm) across the other three systems. Low variability between Cirrus, Spectralis, and the portable Envisu system suggested that hand motion or instability of a human operator does not introduce additional error while holding the hand-held probe over the target. These differences may not affect disease management with uniform scanning protocols and manual measurements based on the small number of pixels required for the observed differences and the larger errors associated with automated segmentation, sampling density, and fixation variability.7,10–13 However, clinical studies gathering repeated measurements over time to evaluate disease modification may obtain statistically significant differences that remain within the range of instrument variability.