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P. Pazienza, S. Tedesco, E. Delfini, A. Lamedica, C. Macaluso; Electrode Montage Affects Parameters and Reproducibility of the Focal Electroretinogram (fERG) . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1668.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effect of two different recording methods on parameters and reproducibility of the focal ERG.
The focal ERG stimulator was an experimental LED–based device (CSO, Florence, Italy), with a central 18° 680 cd/m2 green stimulus and a 100 cd/m2 surround in a ganzfeld dome. Flickering of the stimulus at 41 Hz elicited a steady state retinal response, that was analyzed by means of Fourier analysis, extracting amplitude and phase delay data. The two recording methods differed for the reference electrode, positioned either on the controlateral occluded eye (interocular method) or on the ipsilateral temple (temple method). Focal ERG has been recorded from 66 eyes of 33 subjects with both methods, and it was repeated within the same session in order to evaluate reproducibility.
In both test repeats, correlation between methods was good, with intraclass correlation coefficients (ICC) of 0.84 and 0.79. Bland–Altman analysis of the agreement between the two methods showed that focal ERG amplitude is significantly larger with the interocular method (p<0.01, test t). Reproducibility, as measured with the ICC, was high with both the interocular and the temple methods (0.95 and 0.98, respectively), but the standard deviation (SD) of test–retest differences obtained with the temple method was significantly smaller (0.26 vs. 0.40 microV, p<0.01). In order to verify whether this difference in reproducibility was an artifact due to the larger absolute amplitude of the focal ERG obtained with the interocular method, relative measures were considered, that confirmed the finding (4.8% vs. 7.1%, p<0.01).
While recording the focal ERG using a reference electrode positioned on the occluded contralateral eye increases response amplitude, the finding of a significantly increased variability in test–retest difference when compared to the responses obtained with temple reference, tends to favour the latter method. Moreover, referencing to the ipsilateral temple has the advantage of allowing binocular recording.
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