Effect of color of flash stimulus on variability of flash visual evoked potential latencies

Visual Evoked Potentials (VEPs) are evoked potentials generated in response to visual stimuli. The flash VEP (FVEP) is used less frequently than pattern-reversal VEP (PR-VEP) because; it shows great variations in both latency and amplitude in normal subjects. The advantage of FVEP is its feasibility in non-cooperative subjects, which circumvents the major limitation of PR-VEP. The present study was undertaken to assess the effect of change of color of flashlight on variability of FVEP latencies. Healthy subjects in the age group of 18-30 years underwent the standard stimulus using white light, followed by altered stimuli done with red and blue light. 2 trials were given for each eye, for each type of stimulus. The same set of studies was repeated at the same clock time the following day. The inter-individual and intra-individual variability in the peak latency of P2 and N2 waveforms was assessed using coefficient of variation (COV). Both inter-individual and intra-individual variability was less when monochromatic light was used. Between red and blue FVEP, inter-individual variability was less in blue FVEP and the results of intra-individual variability was inconclusive. Monochromatic stimulation preferably with blue light reduced both inter-individual and intra-individual variability seen in latency of P2 and N2 waveforms in FVEP and hence recommended in preference to standard white stimulus for FVEP recording.