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Pablo A. Barrionuevo, Nathaniel Nicandro, Dingcai Cao; S-, M- and L-cone contributions to human pupil responses under dim illumination conditions. Journal of Vision 2013;13(15):P2. doi: 10.1167/13.15.37.
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Cones, rods and melanopsin contribute to pupillary responses. However, how each type of cones contributes to pupil responses has been rarely studied. In our study, we investigated pupil responses to S-, M- and L-cone flicker inputs under dim illumination conditions. A four-primary Ganzfeldphotostimulator (DiagnosysColorDome) controlled rod and cone stimulations at −0.9 log cd/m2, which is below the melanopsin threshold but above the cone detection threshold. Four types of sinusoidally modulated stimuli (1 Hz, 20% contrast) were used: 1) rod stimuli (modulated rod excitation with a constant S- M- and L-cone excitation); 2) S-cone stimuli (modulated S-cone excitation; constant rod, M- and L-cone excitation); 3) M-cone stimuli (modulated M-cone excitation; constant rod, S- and L-cone excitation); and 4) L-cone stimuli (modulated L-cone excitation; constant rod, S- and M-cone excitation). Pupil sizes were measured using an Eyelink II eyetracker (SR Research) with a 250 Hz sampling rate. Pupil amplitudes and phases were derived by Fourier analysis. The results showed that, overall, the cone (S-, M- or L-) stimuli produced smaller responses than rod stimuli, suggesting rod dominance at −0.9 cd/m2. On the other hand, pupil responses to the M-cone stimuli were larger than for S- or L-cone stimuli. While the M- and L-cone stimuli produced similar response phases (between 0 deg and −50 deg), the S-cone stimuli had a response phase of approximately 180 deg. These results are consistent with L/M-On and S-OFF response characteristics of ipRGCs measured in primate retinas (Dacey et al., 2005).
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