Topography of the long- to middle-wavelength sensitive cone ratio in the human retina assessed with a wide-field color multifocal electroretinogram.

The topographical distribution of relative sensitivity to red and green lights across the retina was assayed using a custom-made wide-field color multifocal electroretinogram apparatus. There were increases in the relative sensitivity to red compared to green light in the periphery that correlate with observed increases in the relative amount of long (L) compared to middle (M) wavelength sensitive opsin mRNA. These results provide electrophysiological evidence that there is a dramatic increase in the ratio of L to M cones in the far periphery of the human retina. The central to far peripheral homogeneity in cone proportions has implications for understanding the developmental mechanisms that determine the identity of a cone as L or M and for understanding the circuitry for color vision in the peripheral retina.