The developed semi-automatic algorithm enables estimation of PIMD-2π in glaucomatous eyes with relevant precision using few segmentations of each captured volume.

The variance for subjects is substantial in relation to those for visits and measurements. Cross-sectional independent group comparisons of levels of NRA are unsuitable, due to considerable subject variation. Levels of NRA differences within subjects between visits can be estimated with acceptable precision. Neuro-retinal rim area (NRA) measurement can be used for long-term follow-up of glaucoma progression.

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Purpose To estimate the sources of variation for Pigment epithelium central limit‐Inner limit of the retina Minimal Distance averaged over 2π (PIMD‐2π), and further to analyse their consequences for clinical measurements of glaucoma. Methods Forty subjects with early to moderate stage glaucoma were included. Three SD‐OCT volumes of the optic nerve head (ONH) were captured at two occasions. Each volume was segmented three times for PIMD‐2π. The magnitude of the sources of variation for PIMD‐2π measurements was estimated with an analysis of variance. Results A 95% confidence interval for mean PIMD‐2π was estimated to 215 ± 12 μm (df = 38). The estimated variance for subjects was 1280 μm2. The within‐subject estimated variance for occasions, volumes and segmentations was 10 μm2, 30 μm2 and 40 μm2, respectively. The within‐subject variances were used to model follow‐up of PIMD‐2π over time. A linear loss rate of 0.05 of baseline PIMD‐2π/year was assumed. A significant PIMD‐2π change could be detected in approximately 16–18 months with evenly spaced visits every 4 or 6 months. Conclusions Due to the small within‐subject estimated variances, a clinically undesirable PIMD‐2π change from baseline can be detected in approximately 18 months. Detection of significant PIMD‐2π loss in a subject requires knowledge of normal age loss and measurement variability.

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