Multifocal electroretinogram in trichromat and dichromat observers under cone isolating conditions

The aim of this study was to obtain information about single cone class driven activity in the inner and outer retina in humans. We examined outer retinal activity with the multifocal electroretinogram (mfERG) and inner retinal activity using multifocal oscillatory potentials (mfOPs). A standard (black-white) stimulus was used, as well as stimuli aimed at isolating a single photoreceptor class. The results of 10 trichromats were compared to those of 2 protanopes and 2 deuteranopes. At both retinal layers we find that trichromats show cone isolating response amplitudes that reflect the expected number of cones and that single- gene dichromats have a similar total number of functioning cones as trichromats. The ratio of the responses of the L- and M-cones is slightly smaller for the mfOPs than for the mfERGs. The results indicate that there are major changes in the gain of retinal signals after the inner plexiform layer.