Relating Head Impacts to Pupillary Light Reflex Metrics and Symptom Reporting in Collegiate Rugby Players Throughout a 7s Tournament

Introduction: : Concussions are common sports-related injury, and repetitive concussions have been linked to long-term neurodegenerative processes [1]. Recently, studies have investigated the cumulative effects of subconcussions: head impacts that do not result in a concussion diagnosis but induce mild concussion-like symptoms. In contact sports, studies have linked frequent subconcussive impact events to cognitive, structural, and functional changes [2].

Recovery from concussions depends on forming a quick and accurate diagnosis that can be used to inform an athlete's return-to-play protocol. However, many of the current methods used to diagnose concussion rely on self-reported symptoms, introducing a subjective element to the diagnosis. Other concussion diagnostic methods, such as balance and cognitive tests, lack reliability and are difficult to perform on the sidelines. To address these limitations, recent studies have looked at pupillometry as a potential fast and objective measure of head impact severity. Concussions and subconcussive head impacts can cause disruptions in the autonomic nervous system, resulting in measurable changes in the pupillary light reflex [3, 4]. Along with aiding in concussion diagnosis, clinical measures like pupillometry have the potential to detect subconcussive head impacts and monitor recovery progression.

Given its high frequency of head impacts and absence of mandatory protective headgear, rugby provides a unique environment for studying repetitive head impacts. In this pilot study, pupillary light reflex metrics and self-reported symptoms were tracked throughout a day of 7s tournament play in male collegiate rugby players.

Materials and

Methods: : Thirteen male collegiate rugby players were observed throughout a day of 7s tournament play. At the beginning of the day, players completed a symptom survey and a pupillary light reflex measurement to establish their personal within-day baseline. The surveys and pupil measurements were repeated after each of three games. The surveys followed the format of the SCAT5 Graded Symptom Checklist, asking players to rate 22 concussion symptoms on a scale from 0 (not experienced) to 6 (severe). These surveys were used to calculate each participant's Symptom Severity Score (SSS), which is the sum of all symptom ratings, and the total number of reported symptoms. Pupil measurements were taken with a PLR-3000 pupilometer (NeurOptics) using a white light stimulus with a duration of 0.8 s and a pulse intensity of 180 µW. The pupilometer recorded the maximum pupil diameter, minimum pupil diameter, percent change in pupil size, latency, average constriction velocity, maximum constriction velocity, and average dilation velocity. These measurements were taken on both eyes then averaged.

Videos of each game were taken from multiple angles using Sony HDR-CX405 cameras. Head impacts were defined as notable changes in the head trajectory due to direct head contact (Figure 1). Four video analysts independently reviewed each impact event, and the event was classified as a head impact if three out of four analysts agreed.

The correlation between cumulative head impacts and change in SSS, number of symptoms, and pupillometry metrics was calculated, along with the correlation between change in SSS and pupillometry metrics.

Results, Conclusions, and Discussions:: Throughout the tournament, there were 26 identified head impacts and no reported concussions. For each player, the cumulative number of head impacts experienced throughout the day was counted, and the change in number of symptoms, SSS, and pupillometry metrics were calculated by subtracting the player’s baseline measurements from their post-game measurements. The absolute values for percent change in pupil size, average constriction velocity, and maximum constriction velocity were used to compare changes in magnitude. There was no correlation between the cumulative number of head impacts and changes in the number of symptoms, SSS, or any pupillometry metric (Figure 2). There was also no correlation between changes in SSS and changes in any of the pupillometry metrics after each game compared to baseline (Figure 3). However, the number of symptoms and SSS significantly increased throughout the tournament, with an average of 2.8 symptoms (p = 0.04) and an SSS of 4.4 (p = 0.03) after the final game compared to an average baseline of 1.2 symptoms and an SSS of 1.5. The head impacts observed in this study, although frequent, were likely not severe enough to result in measurable changes in the pupillary light reflex as observed in previous studies with concussed athletes.

Acknowledgements and/or References (Optional):: References
[1] Broglio, S. P., J. T. Eckner, H. L. Paulson, and J. S. Kutcher. Cognitive decline and aging: The role of concussive and subconcussive impacts. Exerc Sport Sci Rev 40: 138-44, 2012. https://doi.org/10.1097/JES.0b013e3182524273
[2] Slobounov, S. M., A. Walter, H. C. Breiter, D. C. Zhu, X. Bai, T. Bream, P. Seidenberg, X. Mao, B. Johnson, and T. M. Talavage. The effect of repetitive subconcussive collisions on brain integrity in collegiate football players over a single football season: A multi-modal neuroimaging study. Neuroimage Clin 14: 708-718, 2017. https://doi.org/10.1016/j.nicl.2017.03.006
[3] Master, C. L., O. E. Podolak, K. J. Ciuffreda, K. B. Metzger, N. R. Joshi, C. C. McDonald, S. S. Margulies, M. F. Grady, and K. B. Arbogast. Utility of pupillary light reflex metrics as a physiologic biomarker for adolescent sport-related concussion. JAMA Ophthalmology 138: 1135-1141, 2020. https://doi.org/10.1001/jamaophthalmol.2020.3466
[4] Joseph, J. R., J. S. Swallow, K. Willsey, A. A. Almeida, M. T. Lorincz, R. K. Fraumann, M. E. Oppenlander, N. J. Szerlip, and S. P. Broglio. Pupillary changes after clinically asymptomatic high-acceleration head impacts in high school football athletes. Journal of Neurosurgery JNS 133: 1886-1891, 2020. https://doi.org/https://doi.org/10.3171/2019.7.JNS191272