Introduction Changes to the pupillary light reflex (PLR) have been demonstrated in traumatic brain injury and in adolescents with a history of concussion. Assessment of changes to the PLR following concussion has been proposed as a potential biomarker.

Objectives Assessment of the reliability of PLR measurements in a cohort of elite female athletes. Determination of the discriminant validity of PLR metrics in athletes with and without a history of concussion.

Design, Setting and Participants A cross-sectional cohort study of 33 international female field hockey athletes. Exclusion criteria: any neurological or ocular disease, eye trauma, exercise within one hour of testing and athletes taking medication that would affect PLR e.g., antidepressants.

Outcome Measures Three valid pupilometer readings of each eye were obtained using the NeurOptics PLR-3000. Eight PLR metrics were measured; maximum and minimum pupil diameter, percentage of pupil constriction, constriction latency (CL), average constriction velocity (ACV), peak constriction velocity (PCV), average dilatation velocity (ADV) and T75%.

Results NeurOptics PLR-3000 demonstrated good-to-excellent reliability (0.78–0.99 ICC) for all PLR metrics. No statistically significant differences (p>0.05) were demonstrated between those with and without a history of concussion. Trends towards slower PLR metrics (CL, ACV, PCV and ADV) were noted in athletes with a recent concussion (< three months) and athletes with three or more concussions.

Conclusion In this limited pilot study, PLRs have promise as a rapid, reproducible, and objective physiological biomarker for concussion. Further validation is required in larger cohorts alongside investigation of the responsiveness of PLR metrics during acute concussion.