Steady-state pupil size varies with circadian phase and sleep homeostasis in healthy young men

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Summary

Steady-state pupil size tracks both circadian phase and accumulated sleep pressure during extended wakefulness, making it a potential non-invasive marker for assessing alertness state in lighting and workplace contexts. Pupil size variability, by contrast, was linked to subjective fatigue and affective dimensions rather than objective EEG alertness, suggesting these two pupil metrics capture distinct physiological processes.

Key Findings

Robust changes in steady-state pupil size were observed across 29 hours of continuous wakefulness in 20 healthy young men (ages 18–30) under strictly controlled dim-light constant routine conditions.
Steady-state pupil size was significantly associated with motivation and sustained attention performance.
Pupil size variability did not significantly change over the protocol but was linearly associated with subjective fatigue, sociability, and anguish.
No significant associations were found between either pupil metric (size or variability) and objective EEG alertness measures or subjective sleepiness ratings.
Results indicate that steady-state pupil size is more strongly driven by combined sleep homeostatic and circadian influences than by pupil size variability.

Categories

Sleep & Circadian Health: Demonstrates that steady-state pupil size varies robustly with both circadian phase and sleep homeostasis during 29 hours of continuous wakefulness.

The Science of Light: Pupil size measures serve as a non-invasive biomarker of circadian phase and sleep pressure, with implications for lighting standards and assessment tools.

Workplace Performance: Steady-state pupil size was associated with motivation and sustained attention performance, suggesting pupillometry as a practical alertness monitoring tool.