Impact of Photoreceptor Functionality on the Waveform of the Pupil Light Reflex in Mice

Abstract

Abstract: : Purpose: To evaluate the waveform of the pupil light reflex (PLR) in CNGA3^–/–Rho^–/– mice without outer retinal photoreception in comparison to RPE65^–/– and wild type mice. Methods: Baseline pupil area, peak response amplitude (in % of baseline pupil area), maximal contraction velocity, and response duration of the PLR were measured in dark adapted eyes from RPE65^–/–, CNGA3^–/–Rho^–/–, and wild type mice. A full field flash was used to stimulate one eye while the fellow eye was recorded with a scanning laser ophthalmoscope. Results: In previous studies, the waveform of the PLR of RPE65^–/– mice was found to be similar to that evoked by dimmer stimuli in control mice, suggesting loss of retinal sensitivity. Indeed, maximal contraction velocity and response duration of the PLR of RPE65^–/– mice were proportionally reduced to the peak response amplitude that was reduced to 16.8% in comparison to 81.1% in wild type mice. In contrast, the peak response amplitude of the CNGA3^–/–Rho^–/– mice was preserved (79.3%). However, the response duration was 1.5 times prolonged compared to that observed in control mice. The maximal contraction velocity was 60% lower and comparable with the maximal contraction velocity of the RPE65^–/– mice. Conclusions: Whereas the waveform of the PLR was preserved in RPE65^–/– mice with a smaller peak response amplitude compared to wild type mice, CNGA3^–/–Rho^–/– mice presented with a preserved peak response amplitude but the timing of the PLR was out of proportion. This time–to–amplitude dissociation of the PLR is presumably due to the missing image–forming photoreceptors in the CNGA3^–/–Rho^–/– mice.

Keywords: pupillary reflex • photoreceptors • genetics