Pupillary light reflex. (A) Mean pupil diameter is shown for wild-type and Rgs9−/− mice (n = 3 each) over a 20-minute bright blue stimulus. Mice were dark-adapted prior to stimulus-on at time zero. (B, C) Mean waveforms for pupil responses to 1-second stimuli are shown for wild-type, Rgs9+/−, and Rgs9−/− mice. Colored vertical lines behind panels indicate the color and timing of stimuli. (B) A dim blue stimulus (0.001 μW · cm−2 at 480 ± 3 nm, ~1 lux) selectively activates rods (wild type [WT] n = 8; Rgs9+/− = 7; Rgs9−/− = 10). (C) A bright red stimulus (10 μW · cm−2 at 622 ± 3nm, ~25,610 lux) predominantly activates rods and medium-wavelength sensitive cones (WT n = 7; Rgs9+/− = 8; Rgs9−/− = 9). Derived mean ± SEM pupil constriction is shown for the initial response (D) and the residual constriction at 30 seconds post stimulus (E). Pupil responses are shown as a percentage of constriction relative to pre-stimulus baseline. Significance is indicated above the bars: ns = not significant; ***P < 0.001.