0628 Retinal responsivity increases after light therapy and is associated with improved depression: Preliminary findings from a RCT

Abstract Introduction Light therapy is a first line treatment for seasonal depression but not effective everyone. Understanding mechanisms of light may help predict who will successfully respond to treatment. Individual differences in the retina’s responsivity underlie response given prior work linking reduced retinal depression. This study tested if changed across intervention and whether changes were associated with improved Methods Participants diagnosed Major Depressive Disorder, With Seasonal Pattern randomized 6 weeks or cognitive behavioral affective disorder (CBT-SAD). group (N=52) on average 41.9 years (SD=14.8) predominantly women (72%). Retinal was assessed using post-illumination pupil (PIPR), measured mid-day winter pre- post-treatment. The net PIPR (red minus blue) calculated as percent baseline 10-30 seconds post stimulus. Depression severity Structured Interview Guide Hamilton Rating Scale – Affective Disorder version (SIGH-SAD). Using multilevel models, we 1) from post-treatment 2) predicted improvements All analyses included random intercept participant ID controlled age, gender, time testing, pupillary reflex (PLR). Results There significant main effect PIPR, such that increased post-light (b=0.29; SE=0.13; p=0.03). negative association between depression, increases decreases symptom (b= -0.18; SE=0.06; p=0.01). Conclusion It possible an upregulation drives antidepressant effects therapy, either through direct circadian pathways. However, throughout are required discern these mechanistic. Support (if any)