The effect of luminance intrusion on the chromatic VEP response

The use of large-field stimuli to elicit chromatic visual evoked potentials from the S-(L+M) pathway is useful for evaluation of compromised retinas. However the use of large fields has been criticized as containing luminance intrusion due in part to the distribution of macular pigment across the retina. We tested the effects of luminance intrusion on the chromatic component (CII) of the onset VEP waveforms. Over a range of luminance mismatches, the latencies of the chromatic waveform components were unaffected by luminance intrusion. Responses to low spatial frequency luminance onsets are known to be highly variable. Consequently, the affects of luminance mismatches were also highly variable. The degree to which intentional luminance mismatches affected the component latencies depended on the shape of individual achromatic components in the waveforms. However, over a range of luminance mismatches that should encompass that encountered by normal variations in macular pigment, the latencies were unaffected. These results suggest that luminance mismatches due to macular pigment differences across the retina have little effect on the latencies of the chromatic components of the VEP response to large field S cone stimuli.