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Y Han, MA Bearse Jr, ME Schneck, AJ Adams; Comparison of Multifocal Electroretinogram (mfERG) component topographies . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1790.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:The topographies of the multifocal electroretinogram (mfERG) first order kernel (K1) response density and P1 implicit time have been reported in normal subjects. This study characterizes the topographies of the implicit time of a later K1 component (N2) and the response density of the second order kernel (K2) and compares them to the previously described component topographies. Methods:Responses from 12 normal subjects were recorded using a VERIS 4 system and standard condition. Response density, implicit time of P1 and N2 in K1, and K2 response density were measured at each of the 103 stimulated locations to determine their retinal topographies. Eight points at the blind spot and in the corresponding region of the other hemifield were excluded from the topography analyses. Coefficients of variation (CV: an index of inter-subject variability) were also determined. Results: The nasal-temporal asymmetry of the K2 response density (nasal ≷ temporal) is opposite in direction to that of K1. The topography of the K2 response density is steeper than that of K1. The dependencies of response density on eccentricity are well described (R2 ≷ 0.96) by power functions. Both P1 and N2 implicit times show very little nasal-temporal asymmetry. Power functions also describe N2 and P1 implicit times, although less well than for response density (N2 R2 ≷0.87; P1 R2 ≷0.80). The difference in N2 implicit time between central and peripheral retina is larger than that of P1 (∼3 ms vs. ∼1 ms). We removed second order contributions from K1 by shifting and subtracting K2, and found that the N2 topography became even steeper than K1. Therefore, the difference between N2 and P1 topographies does not appear to be due to second order influences. Mean (across all locations) CV of K2 response density is larger than that of K1 (29.3% vs. 22.9%; p <0.001). Mean P1 implicit time CV is larger than mean N2 implicit time CV (3.4% vs. 2.5%; p < 0.001). For N2 (but not P1) the variability of the central response is much larger than other responses. Conclusion: The differences between the topographies of N2 and P1 and between K1 and K2 imply that they have different retinal generators. This, in turn, suggests that retinal diseases may affect the components differentially. Since inter-subject variability of N2 implicit time is less than that of P1, N2 may more sensitively detect abnormalities.
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