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Omar Mahroo, Ruta Sakalauskaite, Christopher Hammond, Trevor Lamb; Recovery of human rod photoreceptors following prolonged illumination, assessed using the electroretinogram. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6122.
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In rodent rods, prolonged light exposures cause substantial transducin translocation from outer to inner segments, causing a five-fold reduction in amplification of phototransduction (Sokolov et al. Neuron 2002;34:95-106). We investigated whether similar reductions occurred in human rods following such exposures.
We recorded ganzfeld scotopic electroretinogram a-wave responses to bright (700 or 1650 scotopic cd m-2 s) and dim (3.1 cd m-2 s) blue flashes delivered before and after 30 min exposure to white light (234 or 1700 cd m-2) in four human subjects with dilated pupils, aiming to estimate circulating current and amplification levels. Rod-system isolated responses were achieved by subtracting responses recorded on a blue rod-saturating background from responses to the same flashes delivered in darkness. In one subject, recovery was compared to previously recorded recoveries following shorter (1 min) exposures.
Rod a-wave responses to bright flashes were reduced or eliminated post-exposure, and recovered over the next 20 min to a steady amplitude. In some experiments, this final amplitude was the same as the pre-exposure level, but in others it was marginally lower. We presumed that any permanent reduction was due to movement of the conductive fibre electrode during these prolonged experiments, and we therefore normalized post-bleach recoveries with respect to this final level. The time-course of recovery of the bright-flash response was similar to previously recorded recoveries after shorter exposures. For the dim flashes, the time-course of recovery of the normalized response was similar to, or lagged only slightly behind, that to bright flashes. Any reduction in amplification constant appeared to be no more than 20-30%.
The five-fold reduction in amplification seen in rodent rods following prolonged light exposures was not seen in our human subjects, suggesting that any reduction in amplification is much smaller or recovers substantially within 5-10 minutes. Also, recovery following such prolonged exposures is similar to recovery after shorter exposures.
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