Effects of pupil diameter and luminance changes on pattern electroretinograms and visual evoked potentials

1. The effects of pupil diameter and pattern luminance changes on the latency and amplitude of pattern electroretinograms (P-ERG) and visual evoked potentials (VEP) were evaluated in five normal adults. Two size checks (15' and 31') were tested monocularly. Two test paradigms were studied. 2. Test paradigm A consisted of three experimental conditions where the independent variable was the pupil diameter: natural pupil, pupil maximally dilated with tropicamide, and pupil maximally constricted with pilocarpine. 3. Test paradigm B consisted of three experimental conditions where the independent variable was pattern luminance. Three luminance settings were tested: 101.6, 39.0 and 7.5 cd/m². 4. There was an inverse linear correlation between the latencies of P-ERG β-wave, VEP N70, P100 and the pupillary diameter with longer latencies as the pupil diameter decreased. The latencies of the β-wave and P100 showed an increase of 2-3 msec/mm of decreased pupillary diameter. 5. There was an inverse linear correlation between the latencies of the P-ERG β-wave and VEP P60, N70, P100 and the stimulus luminance with longer latencies as the luminance decreased. The latencies of the β-wave and P100 showed an increase of 10-15 msec/log unit of decreased retinal illuminance. 6. The effect of pupil size and luminance on the amplitude of P-ERG and VEP showed a trend toward smaller amplitude as the pupil was smaller or the luminance decreased. 7. It is concluded that for the two check sizes tested, increased latency due to decreased pupillary diameter is caused by decreased retinal illuminance. The latency effect of decreased illuminance occurs at the retinal level, with little additional change along the visual pathways and visual cortex.