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Michael Klein, Suresh Viswanathan, Stephen Burns, Gang Huang; Comparison of the multifocal electroretinogram (mfERG) a-wave amplitude and cone density. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1506.
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Studies that have used pharmacological agents in non human primates (e.g., Hood et al., IOVS 2002) indicate that electrical activity of cone photoreceptors, depolarizing cone bipolar cells and horizontal cells are all likely to contribute to mfERG a-wave. The purpose of this study was to examine the relationship between the mfERG a-wave and co-localized cone spatial density individually measured in young healthy human subjects.
mfERGs (0.1-300Hz) were recorded from 4 subjects (20-29 years) with a system from Veris Science (EDI, Inc.) using 2.4 degree unstretched hexagons from 206 retinal locations presented at 30 frames per m-step on a 75Hz monitor with m-sequence exponent of 9 and flash strength 9.9 cd-s/m sq. mfERG a-wave amplitude was measured from baseline at 10 ms on the leading edge of the a-wave. In vivo cone images were obtained at 24 retinal locations using a custom-built Adaptive Optics Confocal Scanning Laser Ophthalmoscope. Cone spatial density was measured from a 100x100 microns centered on the mfERG hexagons at 24 retinal locations.
mfERG a-wave amplitude as well as cone density reduced with increase in retinal eccentricity from the fovea and the a-wave amplitude and cone density were positively correlated for each subject (r2=0.35 to 0.49 and p = 0.0049 to 0.0002). The coefficient of variation (CV) of the mfERG a-wave amplitude across subjects at each retinal location (16-62%) was larger than the CV of the cone density (8-37%) at the same location.
The results indicate that underlying cone density can account for a significant portion of the variance in the mfERG a-wave amplitude across retinal eccentricity but that additional factors are likely to make contributions to the variance of the measured mfERG parameters.
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