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      Pupillary changes after clinically asymptomatic high-acceleration head impacts in high school football athletes

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          Abstract

          OBJECTIVE

          Previous studies have shown that clinically asymptomatic high-acceleration head impacts (HHIs) may be associated with neuronal and axonal injury, as measured by advanced imaging and biomarkers. Unfortunately, these methods of measurement are time-consuming, invasive, and costly. A quick noninvasive measurement tool is needed to aid studies of head injury and its biological impact. Quantitative pupillometry is a potential objective, rapid, noninvasive measurement tool that may be used to assess the neurological effects of HHIs. In this study, the authors investigated the effect of HHIs on pupillary metrics, as measured using a pupillometer, in the absence of a diagnosed concussion.

          METHODS

          A prospective observational cohort study involving 18 high school football athletes was performed. These athletes were monitored for both the frequency and magnitude of head impacts that they sustained throughout a playing season by using the Head Impact Telemetry System. An HHI was defined as an impact exceeding 95 g linear acceleration and 3760 rad/sec 2 rotational acceleration. Pupillary assessments were performed at baseline, midseason, after occurrence of an HHI, and at the end of the season by using the NeurOptics NPi-200 pupillometer. The Sport Concussion Assessment Tool, 5th Edition (SCAT5), was also used at each time point. Comparisons of data obtained at the various time points were calculated using a repeated-measures analysis of variance and a t-test.

          RESULTS

          Seven athletes sustained HHIs without a related diagnosed concussion. Following these HHIs, the athletes demonstrated decreases in pupil dilation velocity (mean difference 0.139 mm/sec; p = 0.048), percent change in pupil diameter (mean difference 3.643%; p = 0.002), and maximum constriction velocity (mean difference 0.744 mm/sec; p = 0.010), compared to measurements obtained at the athletes’ own midseason evaluations. No significant changes occurred between the SCAT5 subtest scores calculated at midseason and those after a high impact, although the effect sizes (Cohen’s d) on individual components ranged from 0.41 to 0.65.

          CONCLUSIONS

          Measurable changes in pupil response were demonstrated following an HHI. These results suggest that clinically asymptomatic HHIs may affect brain reflex pathways, reflecting a biological injury previously seen when more invasive methods were applied.

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          Author and article information

          Journal
          Journal of Neurosurgery
          Journal of Neurosurgery Publishing Group (JNSPG)
          0022-3085
          1933-0693
          November 2019
          November 2019
          : 1-6
          Affiliations
          [1 ]1Department of Neurosurgery,
          [2 ]2Michigan Concussion Center,
          [3 ]3Department of Pediatrics,
          [4 ]4NeuroSport, and
          [5 ]5Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan
          Article
          10.3171/2019.7.JNS191272
          31770721
          f637d5d8-8089-4510-98fb-ea194f29589d
          © 2019
          History

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