Ultraviolet Light–Induced and Green Light–Induced Transient Pupillary Light Reflex in Mice

Abstract

Purpose: To study UV light–induced and green light–induced pupillary light reflex (PLR) in mice and to measure the illumination thresholds of rod-mediated and cone–mediated PLR responses. Methods: We measured dark-adapted transient PLR- in C57BL/6 mice elicited with ultraviolet and green light over an intensity range of 9 log units. To assist in isolating the responses mediated by rods and cones, we studied the PLRs in mouse models presenting pure cone and pure rod functions. We also characterized ERG signals in these mice under the same experimental conditions. Results: The UV light–induced transient PLR has identical intensity-response curves as green light–induced PLR in all the three mice strains. The threshold (5% PLR) of rod-driven PLR is 10⁷∼10⁸ photons cm² s⁻¹, which is 1∼2 log units lower than the dark-adapted ERG b-wave. The threshold of cone-driven PLR is ∼10^12.5 photons cm⁻² s⁻¹ and is similar to that of the cone ERG. Conclusions: We demonstrated that mice have PLR responses under UV stimulation. The cone-elicited PLRs have a threshold that is ∼5 log units higher than that of rod-elicited PLR at both UV and green wavelengths. We observed a divergence between the spectra responses in PLR and ERG. However, the mechanism and implications of this phenomenon are yet to be identified.