Multispot Stimuli Reveal Spatial Organization in the Human Electroretinogram (ERG)

Abstract

As shown in the arterially perfused cat eye, multispot patterns, appropriately adjusted to the receptive field properties of cells in the inner nuclear layer, can abolish the b-wave under certain spatial conditions, even though the total number of quanta and the area illuminated are kept constant (Nelson, Zrenner and Gouras, 1979). This raised the hypothesis, that the b-wave reflects an annular or circular surround structure of the spatially organized ERG-generators.

In order to study similar spatial effects in the human ERG, a multispot pattern was constructed, with the size of the individual spots increasing towards the retinal periphery, according to perceptive field estimations in man. The ERG was recorded in response to the flashed pattern. Defocussing the pattern decreased the b-wave about 40%, even though the total number of quanta and the size of the visual field illuminated were kept constant. This effect cannot be explained by the influence of diffuse stray light; control experiments with homogeneous fields, bars and several checkerboard patterns showed only a comparably small effect.

Since only the spatial configuration of the test pattern can be made responsible for the change of the b-wave amplitude, these data support the idea, that the ERG-generators have a spatial organization of the center/surround type. Therefore, under certain conditions of illumination, the influence of this functional structure can be demonstrated also in the human ERG by means of specific patterns, which take into consideration the inhomogeneous distribution of these ERG-generators.