Towards an electroretinographic assay for studying colour vision in human observers

To determine whether electroretinograms (ERGs) to heterochromatic stimulation can detect and quantify hereditary colour vision deficiency. ERGs were measured to counterphase modulation of red and green stimuli. The total modulation depth of the red and green stimuli was constant. The ratio of red to green modulation was varied, and the responses were measured at two temporal frequencies: 12 and 36 Hz. Subjects were 13 protanopes, 19 protanomalous trichromats, 38 deuteranopes, 16 deuteranomalous trichromats and 22 normal trichromats. The responses are in agreement with previous findings: they were determined by a vector additive input of L- and M-cones (and thus is luminance sensitive) at 36 Hz. At 12 Hz, the responses can be modelled a vector addition of an L-/M-additive response (as determined by the 36 Hz ERGs) and an L-/M-opponent response. From the models, L-cone input fraction (36 Hz) and luminance input fraction (12 Hz) were estimated. The five groups showed different characteristics. However, the signal-to-noise ratio (SNR) at 12 Hz was not always satisfactory. The ERGs to heterochromatic stimuli are potentially interesting for determining the presence and the type of colour vision deficiencies, provided some measures are taken to improve the 12 Hz SNRs.