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A. Tafreshi, G. Vizzeri, R. N. Weinreb, L. M. Zangwill, P. A. Sample, C. Bowd; Within and Between Trial Repeatability of Pattern Electroretinogram Optimized for Glaucoma Detection (PERGLA). Invest. Ophthalmol. Vis. Sci. 2008;49(13):721.
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To determine the within and between trial repeatability of pattern electroretinogram measurements in healthy eyes, using a new clinical instrument, the PERGLA (Glaid, Lace Elettronica, Pisa, Italy).
70 eyes of 35 healthy individuals (IOP < 22 mm Hg, healthy optic disc by stereophotograph assessment, standard visual fields within normal limits) enrolled in the UCSD Diagnostic Innovations in Glaucoma Study (DIGS) (mean age = 61.3, S.D. = 9.7 years, 27 female) were tested twice by a single operator using the PERGLA device. All eyes were refracted and near acuity was J1 for all participants. Repeatability of measurements between two runs within a single trial was compared to repeatability of measurements between two trials (i.e., after electrode replacement) by calculating the coefficients of variability (CVs) and the intraclass correlation coefficients (ICCs).
Average (S.D.) amplitude, phase and signal-to-noise ratio were 0.80 (0.26), 1.81 (0.11) and 5.7 (3.15), respectively. CVs (ICCs) were 11.0% (0.87) and 1.5% (0.89), and 10.2% (0.84) and 1.8% (0.78) for amplitude and phase for within and between trial measurements, respectively. Bland-Altman plots indicated good agreement between the measurements and were similar within and between trials (95% limits of agreement between trials were -0.26 and 0.31 for the amplitude and -0.13 and 0.19 for the phase). 12 eyes of 8 individuals were outside of normal limits based on amplitude and/or phase, as determined by the instrument's internal normative database.
Repeatability of PERGLA measurements is good and is very similar within and between trials, suggesting this technique is promising for monitoring change over time (e.g., little effect of electrode replacement). However, based on previous studies, variability likely is greater in glaucoma patients. Specificity of the normative database was moderate in this population.
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