Study objectives: The regulation of arousal and pupillary functions may be intimately linked via activity in the nucleus locus coeruleus. In this preliminary study, we tested the validity of the gradual pupillary miosis during 5 minutes in darkness, as a quantitative physiologic index of the arousal state of the brain.
Design: Cross-sectional assessment of 2 groups with between-group comparison and correlational analyses within the patient group.
Participants: Eleven unmedicated male patients recently diagnosed with obstructive sleep apnea (OSA) with no comorbid conditions who had undergone polysomnography to assess OSA severity and sleep variables, and 11 sex- and age-matched healthy controls.
Interventions: Sampling of the resting pupil diameter (RPD) over 5 minutes in darkness in the morning and in the afternoon hours, using an infrared video pupillometer.
Measurements and results: The RPD was smaller, indicating a lower level of arousal, in the patient group compared with controls in both the morning and the afternoon; the RPD showed a significant circadian reduction in the afternoon only in the patient group. Within the patient group, the RPD correlated negatively with Epworth Sleepiness Scale scores and Arousal Index and positively with the lowest oxygen saturation during the night. Controlling for the effect of body mass index, the relationship between RPD and subjective sleepiness was lost, whereas the relationship with most of the objective indexes of OSA severity was improved.
Conclusions: The 5-minute pupillary miosis in darkness holds promise as a simple, fast-to-administer, valid, and sensitive test for the objective assessment of excessive daytime sleepiness.