Slowed recovery of human photopic ERG a-wave amplitude following intense bleaches: a slowing of cone pigment regeneration?

We have used the post-bleach recovery of the ERG a-wave to estimate the time-course of regeneration of cone pigment, following bleaching exposures far stronger than in a previous study. We recorded the photopic electroretinogram a-wave from two subjects, in response to dim red flashes delivered following 1-min exposures to intensities ranging from 1.1 × 10(4) to 1.3 × 10(5) photopic cd m(-2). The measured response amplitudes were "linearized" to derive estimates of pigment level. These estimated pigment levels were found to increase at an initially linear rate, consistent with a "rate-limited" model of photopigment regeneration. The extracted time-course was similar to that previously reported in densitometric studies of cone pigment regeneration after similarly intense exposures. On the other hand, the rate of regeneration was slower than measured in the same subjects following less intense bleaches. These results are consistent with the notion that cone pigment regeneration is slowed following very strong bleaching exposures, possibly as a result of depletion of a pool of retinoid.