Scotopic retinal sensitivity in man as determined with visually evoked cortical potentials

Scotopic properties of the peripheral retina in man was studied by recording visually evoked cortical potentials (VECPs). The intensity required for a criterion latency of the scotopic VECP was compared with the sensory threshold in a number of situations where the stimulating retinal site and the area of the stimulus were altered. With circular spot stimulation, the VECT amplitude attenuated greatly as the stimulus site moved to peripheral 10 degrees and was almost null when stimulation was made outside it. However, within the retinal area from the fovea to peripheral 10 degrees, the VECP sensitivity was found to vary according to the rod distribution, as suggested from the sensory threshold. Stimulation with annular patterns revealed that the parallelism between the VECP sensitivity and the rod distribution holds good within up to 30 degrees from the fovea. A strong summation was proved to be operative for eliciting VECPs by stimulation of the peripheral retina.