Quantitative pupillary light reflex abnormalities in acute concussion

Abstract

Background The process of concussion diagnosis following a sports injury remains suboptimal, and currently relies on self-reported symptoms and/or diagnostic "task-based" assessments with subjective and effort-based limitations. The purpose of this study was to evaluate the use of pupillometry light reflex (PLR) as a potential objective physiologic marker in concussion. Methods Six (6) subjects underwent baseline (pre-concussion) PLR testing using a Neuroptics, DP-2000 Binocular Pupillometer. Pupil diameter was recorded for 5 seconds following a brief light stimulus in a single eye. The following values were obtained from the recordings in both the stimulated and consensual eyes: maximum diameter, minimum diameter, percent change, latency, constriction velocity (CV), maximum constriction velocity (MCV), dilation velocity (DV), T75, and RA5. T75 and RA5 represent the time to 75% re-dilation and the re-dilation amplitude from baseline, respectively. Measurements were taken again within 48 hours of concussion, in the same participants. A paired, 2 tailed t-test was used to assess significant changes in these values. Bonferroni correction was applied to account for multiple comparisons. Results RA5, a measure of pupillary sympathetic function, was significantly reduced (p = 0.004) in the post-concussive state compared to preconcussion baseline. Additionally, percent change, a measure of pupillary parasympathetic function, was greater post-concussion compared to baseline, though this did not meet significance following Bonferroni correction (p = 0.007). A similar pattern was seen in the consensual eye, though these differences did not meet significance. Conclusions We demonstrate significant changes in pupillary autonomic function within 48 hours of a concussion. These findings support the potential use of PLR as a biomarker in athletes following concussion, with the potential to yield important mechanistic information about the acute concussive state.