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Variance components for PIMD ‐2 π estimation of the optic nerve head and consequences in clinical measurements of glaucoma
Author(s) -
Sandberg Melin Camilla,
Yu Zhaohua,
Söderberg Per G.
Publication year - 2020
Publication title -
acta ophthalmologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.534
H-Index - 87
eISSN - 1755-3768
pISSN - 1755-375X
DOI - 10.1111/aos.14197
Subject(s) - confidence interval , optic nerve , glaucoma , ophthalmology , analysis of variance , statistics , coefficient of variation , medicine , mathematics
Abstract Purpose To estimate the sources of variation for Pigment epithelium central limit‐Inner limit of the retina Minimal Distance averaged over 2 π ( PIMD ‐2 π ), 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 ‐2 π . The magnitude of the sources of variation for PIMD ‐2 π measurements was estimated with an analysis of variance. Results A 95% confidence interval for mean PIMD ‐2 π was estimated to 215 ± 12 μ m (df = 38). The estimated variance for subjects was 1280 μ m 2 . The within‐subject estimated variance for occasions, volumes and segmentations was 10 μ m 2 , 30 μ m 2 and 40 μ m 2 , respectively. The within‐subject variances were used to model follow‐up of PIMD ‐2 π over time. A linear loss rate of 0.05 of baseline PIMD ‐2 π /year was assumed. A significant PIMD ‐2 π 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 ‐2 π change from baseline can be detected in approximately 18 months. Detection of significant PIMD ‐2 π loss in a subject requires knowledge of normal age loss and measurement variability.