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.

We evaluated the color vision of mercury-contaminated patients and investigated possible retinal origins of losses using electroretinography. Participants were retired workers from a fluorescent lamp industry diagnosed with mercury contamination (n = 43) and age-matched controls (n = 21). Color discrimination was assessed with the Cambridge Colour Test (CCT). Retinal function was evaluated by using the ISCEV protocol for full-field electroretinography (full-field ERG), as well as by means of multifocal electroretinography (mfERG). Color-vision losses assessed by the CCT consisted of higher color-discrimination thresholds along the protan, deutan, and tritan axes and significantly larger discrimination ellipses in mercury-exposed patients compared to controls. Full-field ERG amplitudes from patients were smaller than those of the controls for the scotopic response b-wave, maximum response, sum of oscillatory potentials (OPs), 30-Hz flicker response, and light-adapted cone response. OP amplitudes measured in patients were smaller than those of controls for O2 and O3. Multifocal ERGs recorded from ten randomly selected patients showed smaller N1–P1 amplitudes and longer latencies throughout the 25-deg central field. Full-field ERGs showed that scotopic, photopic, peripheral, and midperipheral retinal functions were affected, and the mfERGs indicated that central retinal function was also significantly depressed. To our knowledge, this is the first demonstration of retinal involvement in visual losses caused by mercury toxicity.