Pupillary Light Reflex Metrics Differ in Adolescents with Acute Concussion VS. Persistent Post-Concussion Symptoms

Abstract

Background: A potential objective measure that may assist in identifying vision disorders after concussion is the pupillary light reflex (PLR), which is under autonomic control and contributes to normal convergence and accommodative function which is altered after concussion. This study sought to compare pupillometry measures in adolescents with concussion initially presenting for care in the early acute time frame (≤ 2 weeks post-concussion) to those presenting in the later acute time frame (4 ± 1 weeks). Hypothesis: To determine whether PLR metrics are similar or different between athletes with concussion presenting earlier (≤ 2 weeks post-concussion) for care vs. those presenting later for care (4 ± 1 weeks). Methods: Athletes, ages 12-18 years, with a diagnosis of sport-related concussion (n = 110) were recruited. 89 concussed subjects had their PLR assessment performed at an early acute time point ≤ 2 weeks after concussion, while 21 concussed subjects had their first assessment at a later acute time point (4 week±1 week). Pupillary dynamics were measured in response to a brief, step-input, white light stimulus (154 ms duration; 180 micro watts power) via a Neuroptics PLR-3000 hand-held, infrared, automated, monocular pupillometer (Neuroptics, Irvine, CA). The means of the PLR metrics were compared between groups with one-way Student’s t test. Bonferroni correction was applied. Results: The baseline pupil diameter (mean ± SD) was significantly larger (p<0.05) for the subjects seen later 4 ± 1 week (5.09 mm ± 0.63) as compared to the cohort of subjects who presented earlier within 2 weeks after injury (4.72 ± 0.79mm). Average constriction velocity ACV for the later-presenting cohort (3.35±0.45 mm/s) was significantly faster compared to the early-presenting cohort (3.04±0.59 mm/s). Similarly, maximum constriction velocity for the groups were significantly different (early 4.82±0.90 versus late 5.31±0.70 mm/s), even after Bonferroni correction (p<0.05), with alpha of 0.025. All the other pupillometric parameters were not different from each other. Conclusion: When comparing adolescents with concussion presenting early in the acute phase ≤ 2 weeks after concussion to those presenting later in the acute timeframe to care 4±1 weeks, those presenting later demonstrate enhancement of certain PLR metrics, namely larger baseline pupil diameter and faster average constriction velocity (ACV) and maximum constriction velocity (MCV). Differences in these PLR metrics in those presenting later in the acute timeframe may represent findings in those who are more likely to have persisting post-concussion symptoms, potentially shedding light on pathophysiological underpinnings of lingering symptoms.