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G. Forma, G. Carboni, M. G. Mutolo, B. J. Jennings, A. Iannaccone; Test-Retest Variability of Measures of Macular Function: Baseline Findings From the Zeaxanthin Pilot Study of Response to Supplementation (ZEASTRESS-Pilot). Invest. Ophthalmol. Vis. Sci. 2010;51(13):2801.
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To assess the short-term test-retest variability in psychophysical and electrophysiological macular function tests obtained at baseline in ZEASTRESS-Pilot participants to be used for longitudinal assessment of response to 20mg zeaxanthin supplements.
Twenty White volunteers were enrolled. Of them, 18 were eligible for retention and completed the two required baseline qualification visits (QV1/QV2) within 3 weeks (mean age: 58.39 ± 5.15 years old; range: 50-66; M/F=7/11). Four outcome measures were assessed for test-retest variability in a clinical research setting: number of letters read to contrast sensitivity (CS) testing with Pelli-Robson charts; P50 amplitude of the pattern-reversal electroretinogram (PERG) to 45 minarc, 100% contrast, black & white, 2.0-Hz stimuli; dark-adapted foveal cone sensitivity at 650 nm (DA-650 FCS); and parafoveal (2-deg eccentricity) rod sensitivity at 500 nm (DA-500 PFRS), measured with a custom-modified Humphrey perimeter. Pearson’s correlation coefficients, r, and coefficients of variation (CV) were calculated for each outcome measure.
All tests displayed excellent reproducibility. CS was strongly correlated between QV1 and QV2 (Pearson’s r = 0.840) and the CV was 1.17% (± 2.03, SD). The intersession r for the PERG P50 was 0.946 and the CV was 4.00 ± 2.53%. DA-650 FCS and DA-500 PFRS were also highly correlated between sessions (Pearson’s r = 0.744 and 0.908; CV: 2.29 ± 1.29% and 1.37 ± 1.13%, respectively).
CS assessed by Pelli-Robson charts, PERG P50 amplitudes, DA-650 FCS and DA-500 PFRS displayed excellent test-retest variability with average CVs 4% or less in all cases. These measurements appear very well suited for studies of macular function and response to supplementation with zeaxanthin, similar carotenoids, and other agents that may improve macular visual performance. These CV estimates can be used to calculate the sample sizes necessary to achieve statistical significance when testing hypotheses about the efficacy of any such intervention.
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