Figure 5: Measuring the effect of scan position on accuracy of ETDRS thickness plots. For each subject, we estimated this error by comparing the raw ETDRS thickness plot to one that has been repositioned to be centered on their fovea. In the normal individuals (a), the summed error across the nine ETDRS segments could be as much as 100 μm, while in individuals with pathology (b) the error could exceed 200 μm. For some pathology cases, nonfoveal fixation can be compensated for by moving the location of the OCT scan. For 2 individuals, we acquired scans at their eccentric fixation location (filled triangle and diamond) and a second scan after the operator manually moved the scan to be centered on the fovea (open triangle and diamond, connected by thin gray lines). Even when using the repositioned scan, residual error remains, though it is on the order of that observed for the other patients.