THE UTILITY OF PUPILLARY LIGHT REFLEX AS AN OBJECTIVE BIOMARKER OF ACUTE CONCUSSION IN THE ADOLESCENT ATHLETE

Abstract

Background: Visual deficits and autonomic dysfunction have been well recognized following pediatric concussion. Testing of the pupillary light reflex (PLR) is a simple, non-invasive, and objective approach to examine the autonomic nervous system by accessing the brain pathways. The aim of this study was to objectively evaluate adolescent pupillary responses to a light stimulus after a physician-diagnosed concussion and compare them to baseline responses. Methods: In this prospective cohort study, PLR was assessed in 135 adolescent athletes (ages 14-18) during their sport pre-season. All of the athletes were not recovering from a concussion at the time of their baseline assessment. Within this cohort, seven athletes (ages 14-17) sustained a concussion during their sport season and had longitudinal post-injury assessments of PLR through their recovery. The PLR was obtained in response to a brief step-input (0.8 seconds) white light stimulus using a hand-held pupillometer (stimulus recording duration= 5 seconds, light intensity= 150 lux). Pre-set and automated device-generated parameters used for analysis include the minimum and maximum pupil diameter, response amplitude and latency, mean constriction and dilation velocities and the maximum constriction velocity of the eye in response to a light stimulus. During each assessment, three monocular trials were performed in each eye alternatively, and the responses for each eye were subsequently averaged. Results: Six out of the seven concussed adolescents showed response enhancement of about 20% (IQR 11-33%). Enhancement was noted in the steady state diameter with a mean of 24% (median 18%), minimum pupil diameter mean of 17% (median 11%) and maximum constriction velocity mean of 28% (median 33%) following concussion, which decreased during the recovery process (days to weeks post-injury) to pre-injury or below initial pre-injury baseline measurements. Pupillary responsivity was found to be significantly enhanced after concussion compared to baseline measurements, waning over time. Maximum constriction velocity better highlighted the enhancement compared to the baseline pupil diameter. Conclusions/Significance: Pupil responsivity was found to be significantly enhanced after concussion compared to baseline measurements which waned over time during recovery. Assessment of dynamic PLR responses has potential utility as an objective biomarker to aid in concussion diagnosis on the sidelines or in the office, allowing physicians to quantify function (and dysfunction) of the autonomic nervous system under parasympathetic and sympathetic control after concussion.