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C. M. Tosha, M. B. Gorin, S. Nusinowitz; Test-Retest Reliability and Inter-Ocular Symmetry of Multi-Focal Electroretinography (mERG). Invest. Ophthalmol. Vis. Sci. 2009;50(13):4518.
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To evaluate test-retest reliability and inter-ocular symmetry of mERG recordings in Stargardt disease (STGD) and in patients without retinal pathology.
ERGs were recorded with the VERIS multifocal recording system using an array of 103 hexagons covering 30 degrees of central retina. ERGs were recorded with continuous fundus monitoring to ensure central fixation. Recordings were made sequentially from one eye (test-retest) followed by recordings from the fellow eye. For both test-retest and inter-ocular analyses, first-order mERG responses were compared at each of the 103 locations, and for six rings concentric with the macula. A departure score, expressed as a percentage difference from reference, was calculated for each comparison. Coefficient of Variance (CV) was used to assess signal-to-noise in each region.
mERG response topographies were similar within and between eyes for a particular individual. However, local response variability was significantly higher in STGD than in normal subjects. Test-retest variability was larger in STGD than for normal, with significant heterogeneity across patients (STGD = 18.9%, SD=7.5; Normal =14.8%, SD=3.0). mERG responses in STGD were more variable in paracentral regions, with reduced variability in the macular region (due to basement effect) and in more peripheral regions; the variability across regions in normal subjects was constant. Inter-ocular variability of mERGs in STGD was 2.0 times larger than that for normal (STGD =31.7%, SD=14.8; Normal=14.6%, SD<0.01). CV in each region was correlated with test-retest and inter-ocular reliability (p<0.05).
mERG test-retest reliability is significantly higher in STGD compared to normal, a finding we attribute to small eye movements despite continuous fundus monitoring. Intra-ocular variability may also reflect pathological differences in the topography of retinal function. This inherent variability must be taken into consideration if the mERG is to be sufficiently sensitive to reliably detect small changes in retinal function in a clinical trial.
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