Differences in the Pupillary Responses to Evening Light between Children and Adolescents

To assess differences in the pupillary light responses (PLRs) to blue and red evening lights between children and adolescents.

Forty healthy participants (8-9 years, n=21; 15-16 years, n=19) completed a PLR assessment 1 h before their habitual bedtime. After a 1 h dim-light adaptation period (<1 lux), baseline pupil diameter was measured in darkness for 30 s, followed by a 10 s exposure to 3.0×10¹³ photons/cm²/s of either red (627 nm) or blue (459 nm) light, and a 40 s recovery in darkness to assess pupillary re-dilation. Subsequently, participants underwent 7 min of dim-light re-adaptation followed by an exposure to the other light condition. Lights were counterbalanced across participants.

Across both age groups, maximum pupil constriction was significantly greater (p< 0.001, η_p²=0.48) and more sustained (p< 0.001, η_p²=0.41) during exposure to blue compared to red light. For adolescents, the post-illumination pupillary response (PIPR), a hallmark of melanopsin function, was larger after blue compared with red light (p= 0.02, d=0.60). This difference was not observed in children. Across light exposures, children had larger phasic (p< 0.01, η_p²=0.20) and maximal (p< 0.01, η_p²=0.22) pupil constrictions compared to adolescents.

Blue light elicited a greater and more sustained pupillary response than red light across participants. However, the overall amplitude of the rod/cone-driven phasic response was greater in children than in adolescents. Our findings using the PLR highlight a higher sensitivity to evening light in children compared to adolescents, and continued maturation of the human non-visual photoreception/system throughout development.