Changes in Pupils After Asymptomatic High-Acceleration Head Impacts Indicate Changes in Brain Function

December 4, 2019

Researchers have found significant pupillary changes in high school football athletes after they had sustained a high-acceleration head impact, and the changes were detected using a noninvasive, hand-held, quantitative pupillometry (QP) device, which potentially could be used in a nonclinical setting for a quick assessment of possible brain injury.

Previous studies have found associations between high-acceleration head impacts and neuronal and axonal injury, even in the absence of symptoms and diagnosis of concussion. However, these studies have relied on the results of invasive tests, such as biomarker analysis and advanced neuroimaging, which are expensive, time-consuming, and not always readily available.

For the current study, published in the Journal of Neurosurgery, Jacob R. Joseph, MD, University of Michigan, Ann Arbor, Michigan, and colleagues looked at the potential of QP as an objective, fast, and noninvasive method to assess the neurological effects of high-acceleration head impacts when no symptoms are apparent. QP provides objective, quantifiable data on changes in pupil size and reactivity to light. Such changes can reflect changes in brain function.

A total of 13 high school football players completed the entire study. Sensors were placed in these athletes’ football helmets to measure and record the frequency and intensity of head impacts during all practices and games in a football season. Data on all head impacts were collected for each athlete. The focus of this study was on high-acceleration head impact, which was defined as an impact that simultaneously exceeds 95-gravity linear acceleration and 3760-radian/second2 rotational acceleration.

QP was performed to measure each athlete’s pupil size and reactivity to light (in all, 8 parameters of the pupil) at various time points throughout the playing season and to compare these measurements with normative data. Testing only took 2 minutes per session, and in each instance, the ambient lighting was similar. Testing was performed before the playing season began; at the middle of the season, following a game; after the season had ended; and in athletes who sustained a high-acceleration head impact, following the practice session or game in which the impact occurred.

At the time of pupillometry testing, the athletes also underwent neurocognitive testing to determine whether the impacts produced concussive injuries. This was performed using the Sport Concussion Assessment Tool, 5th Edition. The authors focused on evaluations of symptoms, cognitive screening, balance assessment, and delayed recall.

A total of 7 athletes experienced high-acceleration head impacts without a related concussion diagnosis during the playing season -- 6 of them before the midseason evaluation. In a comparison of QP measurements obtained following high-acceleration head impacts with those obtained at the midseason evaluation (control), the authors found significant decreases in 3 of the 8 QP parameters, specifically pupil dilation velocity, percent change in pupil diameter, and maximum pupil constriction velocity.

In a comparison of QP measurements across the playing season (measurements obtained at baseline, midseason, and end-of-season evaluations), the authors found significant changes in 2 QP parameters, namely average pupil constriction velocity and maximum pupil constriction velocity.

The authors found no significant changes in neurocognitive test values when they compared values obtained following a high-acceleration head impact with values obtained at the midseason evaluation. They also found no significant changes when they compared neurocognitive test values across the playing season.

The authors stressed that the sample of athletes evaluated in this study is small and the study is preliminary. Their findings need to be confirmed in a larger study.

Reference: https://thejns.org/view/journals/j-neurosurg/aop/article-10.3171-2019.7....

SOURCE: Journal of Neurosurgery Publishing Group