Purpose. To determine, first, which regions of 3-D optical coherence tomography (OCT) volumes can be segmented completely in the majority of subjects and, second, the relationship between analyzed area and thickness measurement test–retest variability. Methods. Three-dimensional OCT volumes (6 × 6 mm) centered around the fovea and optic nerve head (ONH) of 925 Rotterdam Study participants were analyzed; 44 participants were scanned twice. Volumes were segmented into 10 layers, and we determined the area where all layers could be identified in at least 95% (macula) or 90% (ONH) of subjects. Macular volumes were divided in 2 × 2, 4 × 4, 6 ...