LAUSR

Seasonal affective disorder (SAD) is characterized as patterned depressed mood that emerges during the fall/winter and enters remission during the spring/summer. Retinal responsivity is lower in SAD in the winter and may contribute to the seasonal pattern of mood disruption (Roecklein et al., 2021). Light exposure in the month prior has been shown to influence retinal responsivity (Kawasaki et al., 2018). No work to date has investigated how more proximal prior light history may influence retinal responsivity differently in individuals with SAD versus controls. This study sought to examine group differences in how environmental blue light exposure impacts retinal responsivity in the 2 hours prior. Participants included 19 never depressed controls (Mean Age = 33, SD = 11), and 17 individuals diagnosed with SAD (Mean Age = 36, SD = 10). SAD episode criteria were assessed using the SCID-5 and SIGH-SAD. Retinal responsivity was measured using the Post-Illumination Pupil Response (PIPR) in the winter months. The PIPR was calculated as percent of baseline difference between the blue and red stimuli from 10-30 secs. Light exposure was measured using the Phillips Actiwatch blue light levels in photon flux in 30-second epochs for 2 hours before the PIPR. Means were calculated and cube transformed to account for right skew. Covariates included circadian time of PIPR testing, calculated from DLMO, and Pupil Light Reflex as a measure of retinal irradiance. Multiple regressions were performed for the SAD and control groups, separately. Results indicated that the mean blue-light exposure 2-hours before the PIPR did not significantly predict PIPR in either group (Control group: b = -13e-7, p = 0.31/ SAD group: b = -12e-7, p = 0.13). This is the first study to find that light exposure within the prior 2 hours does not influence retinal responsivity in SAD or control participants. Future studies should evaluate different light exposure parameters, such as a longer duration of light exposure before the PIPR, variation in light exposure across different timeframes, and circadian time of light exposure.