Vector analysis of visual evoked potentials elicited by pattern reversal and photic stimuli.

Abstract Objective : The 2D VEPs to pattern reversal (PR) and LED goggle were studied in order to obtain a stable parameter for the functional assessing of posterior visual pathways regardless of the stimulus type used. Design and methods : Apex c latency, bc segment amplitude ( V ), and bc vector orientation angle ( θ ) in voltage space were computed from VEPs recorded in 50 normal human beings and two patients with left posterior brain lesions, in an orthogonal Fpz–Oz and T3–T4 montage and displayed as a two channel Lissajous’ trajectory. The effects of stimulus type and stimulated eye were analyzed in the normal group by a two-way ANOVA. Results : The stimulated eye had no effect on any parameter. Apex c latency was slightly longer, and V was greater and more variable in the responses to goggle stimuli, but there was no significant difference in θ , oriented to mid-occipital scalp with very low variability for both stimulus types. The patients showed significant deviations of θ towards the affected hemisphere. Conclusions : The bc vector orientation ( θ ) is a stable parameter for the evaluation of the posterior visual pathways using both pattern reversal and LED stimuli, specially the latter, useful in unconscious or uncooperative patients.