The Blue Cone Electroretinogram Isolated in a Sex-Linked Achromat

Abstract

A blue cone monochromat identified by psychophysical methods was studied by electroretinography (ERG), using spectrally selective stimuli, i.e. blue, green and yellow full-field test lights on full-field backgrounds. In the absence of a background the scotopically most effective stimulus (green) produced the largest ERG and scotopically-matched stimuli (blue = green = yellow) produced univariant responses; only the strongest blue stimulus produced a slight break in univariance It was therefore presumed that these ERGs were mediated almost exclusively by rods. With a 69 cd/m2 yellow adapting field the ERGs to rod-matched yellow and green stimuli remained univariant but those to blue were not, being significantly quicker in time course. With a 103 cd/m2 white adapting field, no responses could be detected with green and yellow stimuli but only the quick response to blue light remained. It was concluded that this was the blue cone ERG. It had both an a- and b-wave, the latter being much larger (5 microvolts). At mesopic levels (yellow background) the early ‘blue’ cone ERG produced by blue light was not followed by the slower rod response known to be elicited by this blue stimulus (seen in the response to longer wave scotopically-matched stimuli), implying that the earlier blue cone response weakens or suppresses the later rod response.