Assessing the clinical utility of pupillary light reflex in youth with emerging mood disorders

Background: Altered sensitivity to light is a potential mechanism for developing abnormal circadian entrainment. This study investigates the utility of the pupillary light reflex as a method of differentiating youth with emerging mood disorders and healthy controls. Methods: This ongoing study included 58 participants (Mean age=25.86±5.45; 62% Females) aged 14-40 years, seeking mental health care at headspace services in Sydney, and 24 healthy controls (Mean age =25.21±2.59; 54% Females). Participants underwent a 20-min pupillometry assessment to examine the pupil’s response to light. A handheld PLR-3000 Monocular Pupillometer (NeurOptics, California, USA) was used to measure the reflex in a dark room, by delivering two 1-second light pulses (dim [~10 lux] followed by bright [~1500 lux]). Analyses of covariance were conducted to assess group differences, with within-group correlation analysing between pupil metrics and mental health scores. Results: After a dim light pulse, the diameter of the pupil of cases changed significantly less than that of healthy controls (dim: F(1,56)=10.176; pFDR=0.026); bright: F(1,56)=7.480; pFDR=0.039). In addition, the latency of constriction after a bright pulse was significantly longer in cases compared to controls (F(1,56)=8.945; pFDR=0.026). Within cases, change in pupil size and constriction velocity after a bright pulse was positively correlated with psychological distress (K10) and anxiety (GAD-7) scores. Conclusion: These preliminary findings support the potential for pupillary light reflex to clinically differentiate between youth with emerging mood disorders and healthy controls. Future studies will aim to assess the variance in pupillary light reflex between different clinical groups.