Temporal characteristics of melanopsin inputs to the human pupil light reflex

The 6-second post-illumination pupil response amplitude is independent of inter-stimulus interval and temporal frequency for all melanopsin excitation levels.

• The intrinsic signaling properties of melanopsin differ from those of rods and cones, featuring longer latencies and sustained signaling after light ends.
• Maximum pupil constriction increases with longer inter-stimulus intervals, but the time taken to reach minimum diameter is slower with high melanopsin excitation.
• High melanopsin excitation reduces the amplitude of phasic pupil responses compared to low melanopsin excitation.
• There may be two possible sites for outer retina summation that affect pupil diameter control in response to rapid changes in light.

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