Acute Mental Stress is Associated With Altered Pupillary Light Reflex.

Pupillary light reflex (PLR), i.e. pupil constriction in response to light stimulus, offers a sensitive index of parasympathetic nervous regulation. Yet, the studies on PLR in acute mental stress are rare. We aimed to study potential changes of PLR to acute mental stress in healthy young people with respect to sex. Thirty-eight participants (24 women, age: 22.95+/-0.19 yrs) were examined in a cross-sectional study under standard conditions. PLR parameters were measured separately for both eyes using PLR-2000 (NeurOptics, USA) before arithmetic test (baseline), immediately after arithmetic test, and after recovery period. Evaluated PLR parasympathetically-mediated parameters: pupil diameter (mm) before (initial value, INIT) and after illumination (peak of constriction, END), maximum constriction velocity (MCV), relative constriction amplitude (RCA). INIT and END diameters were significantly reduced immediately after mental stress and after recovery compared to baseline (left eye: INIT: p=0.044, p=0.035, respectively; END: p=0.004, p<0.001, respectively; right eye: INIT: p<0.001, p=0.002, respectively; END: p<0.001 for both comparisons). No significant differences were found in MCV and RCA. Moreover, the study established no significant changes in the assessed PLR parameters between sex throughout the stress protocol. Our study revealed that acute mental stress is associated with greater PLR-parasympathetic response resulting in prolonged pupil constriction. This finding could represent the first step for understanding the effect of cognitive processing on PLR under physiological conditions, before its clinical application. Key words Pupillary light reflex " Acute mental stress " Cognitive processing " Parasympathetic nervous system " Psychophysiology.