Major depressive disorder is associated with abnormal autonomic regulation which could be noninvasively studied using pupillometry. However, the studies in adolescent patients are rare. Therefore, we aimed to study the pupillary light reflex (PLR), which could provide novel important information about dynamic balance between sympathetic and parasympathetic nervous system in adolescent patients suffering from major depression. We have examined 25 depressive adolescent girls (age 15.2±0.3 y ear) prior to pharmacotherapy and 25 age/gender-matched healthy subjects. PLR parameters were measured separately for both eyes after 5 min of rest using Pupillometer PLR-2000 (NeurOptics, USA). The constriction percentual change for the left eye was significantly lower in depressive group compared to control group (-24.12±0.87 % vs. - 28.04±0.96%, p˂0.01). Furthermore, average constriction velocity and maximum constriction velocity for the left eye were significantly lower in depressive group compared to control group (p˂0.05, p˂0.01, respectively). In contrast, no significant between-groups differences were found for the right eye. Concluding, this study revealed altered PLR for left eye indicating a deficient parasympathetic activity already in adolescent major depression. Additionally, the differences between left and right eye could be related to functional lateralization of autonomic control in the central nervous system., A. Mestanikova, I. Ondrejka, M. Mestanik, D. Cesnekova, Z. Visnovcova, I. Bujnakova, M. Oppa, A. Calkovska, I. Tonhajzerova., and Obsahuje bibliografii