Effect of pre-adaptation on pattern electroretinogram (P-ERG)

Up to now light and dark adaptation are considered as of minor importance when recording the pattern electroretionogram (P-ERG) which in man reflects cone vision. In order to test this supposition transient P-ERGs were recorded in six healthy subjects to a reversing checkerboard pattern produced by a pivoted mirror system after two minutes of pre-exposure to darkness (1), to the pattern reversal stimulus (2), and to uniform illumination of 3.3 log cd/m2 (3). Field size was 18 x 20 degrees, check size 69 min of arc, reversal frequency 3.5/s, contrast 0.95. When recording the P-ERG within the first 30 s after pre-exposure, the amplitude/luminance function of the p-q and the q-r component was shifted along the luminance axis without changing the maximum amplitude. For a criterion response of 1.5 microV there was a sensitivity difference of 1.3 log units between measurements after pre-exposure to darkness and after strong illumination. Furthermore, the P-ERG latencies of the q and the r component displayed significantly shorter values after pre-exposure to strong light than after darkness, whereas no change of p-latency was recorded. We conclude that pre-exposure to darkness and strong illumination has no effect on the P-ERG elicited at high luminance levels. However, pre-adaptation should be considered when recording the P-ERG at luminance levels near threshold.