The influence of ambient room lighting on the pattern electroretinogram (PERG)

It has been suggested that low ambient lighting conditions increase the amplitude of the PERG, but no data has been available on this issue. We recorded the transient PERG (0.8 degrees check size) and steady-state PERG (15 rev/s, 0.8 degrees and 16 degrees check size) under three lighting conditions: dark room, only illuminated by the stimulus (resulting in 30 lux), our standard room lighting (windows occluded, one lighted lamp, 200 lux) and fully lit room (full ceiling illumination with eight fluorescent tubes) resulting in rather bright 2300 lux. The stimulus luminance was 50 cd/m2. The sequence of lighting conditions varied for each subject and followed a balanced permutation of an ABCCBA scheme. Results showed a significant effect (P < 0.01) across lighting conditions, with no relevant difference between the 30 and 200 lux conditions, but a reduction down to 70% at the 2300 lux condition. This obtained across all check sizes and temporal conditions. As an example, the transient PERG P50-amplitudes were as follows: dark, 5.6 +/- 0.8 microV; medium, 5.3 +/- 0.6 microV and bright, 3.8 +/- microV (mean +/- SEM). Peak times decreased significantly with illumination (dark, medium or bright): 45.9 +/- 0.9, 43.1 +/- 0.6 or 40.8 +/- 0.8 ms. Contrast measurements quantitatively explained the noticeable reduction of PERG amplitude at the brightest illumination level simply by straylight, which reduced the display contrast. This suggests that bright sunlight should be excluded, and that lighting conditions should be moderately standardized at low or medium luminance levels for reproducible amplitudes and peak times.