Introduction: Pupillary light reflex (PLR) testing has shown sensitivity to Sport Related Concussion (SRC) and is widely accepted as an indicator of autonomic performance. Longitudinal PLR data could provide insights for return-to-play decisions following SRC as it is a quick non-invasive test that requires minimal cognitive effort from the participant. SRC is suggested to have long term impacts on autonomic function, yet there is limited application of longitudinal PLR testing post SRC. This was a pilot study to compare Sensory Organisation Testing (SOT), a known measure of SRC, with PLR measures at various time points following SRC. Methods: Using a quasi-experimental design, six professional male collision sport athletes (age 20-30) underwent baseline PLR testing (Prism Neuro P/L) and SOT (Bertec Corp) at the beginning of a competition season. Players with a medically diagnosed SRC during the season underwent post-concussion testing at the following timepoints: acute phase (0-2 days post), recovery phase (3-10 days post) and return-to-play phase (11-18 days post). As a pilot study with a small number of participants, results are presented as percent changes only, tests of statistical significance were not applied. Results: Percentage change in group average SOT scores compared with baseline at (0-2, 3-10, 11-18) days respectively were: Composite (-7, 12, 1); Somatosensory (-2, 2, -2); Visual (-5, 19, 0); and Vestibular (-13, 21, 7). Individual result ranges for percentage change in score compared with baseline at the three timepoints were: Composite (-17 to 0, -6 to 19, -4 to 23); Somatosensory (-4 to -1, -4 to 5, -7 to 2); Visual (-23 to 26, -1 to 38, 2 to 41) and Vestibular (-41 to -7, -15 to 20, -10 to 62). Percentage change in group average PLR metrics compared with baseline were: Constriction Latency (3, 1, -1); Peak Constriction Velocity (-1, -11, 14); and Response Amplitude (1, -18, 15). Individual result ranges for percentage change in score compared with baseline at the three timepoints were: Constriction Latency (-2 to 4, -3 to 12, -2 to 6); Peak Constriction Velocity (-3 to 22, - 22 to 12, -13 to 15); Response Amplitude (-18 to 34, -29 to 28, -16 to 27). Discussion: This study has demonstrated the feasibility of testing PLR longitudinally in collision sport athletes post-concussion. SOT deficits peaked in the acute phase, whereas PLR deficits peaked later within the recovery phase. The individual nature of SRC was seen in the results where one athlete may show notable PLR deficits with minor SOT issues, and another may show SOT deficits with no effect on PLR. Different recovery rates indicate different physiological mechanisms underlying each test. SOT is reliant on vestibular and visual-vestibular interaction, while PLR is reflexively controlled by the autonomic nervous system. Autonomic system deficits resulting from SRC may continue beyond the resolution of vestibular issues, and PLR may be a useful tool for monitoring recovery. Impact/Application to the field: This project supports the feasibility of adding PLR as objective data for evaluating SRC return-to-play decisions. Declaration: The lead author holds shares in Prism Neuro Pty Ltd and has conflict of interest management plans in place with the University of Canberra Research Institute for Sport and Exercise and the Australian Institute for Sport.
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