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Nima Fatehi, Sharon Henry, Joseph Caprioli, Kouros Nouri-Mahdavi; Between-session vs. within-session variability of local macular optical coherence tomography (OCT) thickness measurements. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2121.
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© ARVO (1962-2015); The Authors (2016-present)
To estimate the contribution of within-session and between-session variability to total variability of local macular OCT parameters.
Three 30x25 degrees Macular Cubes were acquired at 3 separate sessions with the Posterior Pole Algorithm of Spectralis OCT (Heidelberg Engineering). OCT images were segmented and the thickness of individual retinal layers were calculated. Outcomes of interest were the proportion of total variability explained by between-session variability vs. within-session variability for the ganglion cell layer (GCL), ganglion cell /inner plexiform layers (GCIPL), ganglion cell complex (GCC), and full macular thickness measurements. Only the central 36 (6x6) superpixels of the 8x8 array were used for analysis. Linear mixed effect models were used to estimate the components of variability for macular thickness parameters. Diagnosis and the location of OCT superpixels were considered as fixed effect variables, and imaging session and patient ID were fit as variables with random effects.
Thirty-eight eyes of 20 subject (14 glaucoma patients and 6 normal subjects) were included in the study. The mean (±SD) age was 62.8 (± 10.9) and 46.3 (± 9.9) years, and median (IQR) mean deviation (MD) was –3.1 (–4.6 to –0.9) and 0.51 (–1.4 to 1.1) dB in glaucoma patients and normal subjects, respectively. The mean (± SD) absolute difference among the 9 repeat OCT images across all superpixels was 1.2 (± 0.6), 1.6 (± 0.6), 1.8 (± 0.8) and 1.7 (± 0.7) µm for GCL, GCIPL, GCC and FMT, respectively (Figure 1). The ratios of the mean absolute difference to the mean superpixel thickness were significantly different between all four layers (GCL>GCIPL>GCC> FMT; p-value <0.001, Kruskal-Wallis rank test). The contribution of between-session variability to total variability was 8%, 11%, 11% and 36% for GCL, GCIPL, GCC and FMT, respectively.
This study confirms the very low and uniform variability of all macular thickness parameters. Within-session variability of macular OCT images explains most of the total variability. Repeat imaging on multiple sessions is not needed for defining eye-specific limits of variability with macular OCT imaging.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure 1. Box plot showing the mean absolute difference of 9 repeat OCT images at each superpixel. The pair wise mean differences were statistically different among all four layers (P <0.001).
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