Pupillary Light Reflex Metrics as an Objective Biomarker for Sport-Related Concussion in Elite Field Hockey

Background Concussion diagnosis is based on subjective assessment of several nonspecific clinical signs and symptoms with no objective test to aid in diagnosis. The pupillary system, in particular the pupil light reflexes (PLR) has attracted plausible consideration in this area, given its complex neural circuitry and autonomic function. Aim To assess the reliability and validity of using the NeurOptics PLR-3000 pupilometer to measure PLR, and to determine normative data for female athletes. Methods A cross sectional cohort study of 33 senior elite female field hockey athletes (aged 19-34 years) were recruited. Three valid pupillometry readings were acquired, per eye. Measurements of nine PLR metrics were obtained. Reliability was determined using intraclass coefficients, standard error of measurement (SEM), and minimum detectable change (MDC). Between group differences (concussion history vs. controls) were analysed using non-parametric tests. Results NeurOptics PLR-3000 showed good to excellent reliability for eight PLR metrics derived from the pupilometer [latency, average constriction velocity (ACV), peak constriction velocity (PCV), average dilation velocity (ADV), T75%max. pupil diameter, min. pupil diameter and percent constriction]. There was no statistical difference between any of the PLR metrics in athletes who had a history of concussion and those that had no history of concussion. The two athletes with a recent history of concussion (< 3 months) showed trends towards slowed latency, ACV, PCV and ADV when compared to controls. Conclusion This research does not support previous research that the PLR-3000 is an accurate instrument for distinguishing between those with and without a history of concussion. However, the ICC values for intratester reliability were good to excellent for most PLR metrics, with data comparing favourably to normative values previously reported from other populations. Some PLR metrics may distinguish between distinct group of female athletes (recent history of concussion), but this is a small sample size and exploratory in nature. Larger studies are required to confirm its validity and responsiveness.