Concussions remain one of the most common injuries in youth and professional sports, with up to 3.8 million incidents estimated each year in the U.S. alone. While public awareness and protocols around concussion have improved, objective diagnostic tools remain limited. Clinical assessments still rely heavily on self-reported symptoms, sideline checklists, and observational data.
These limitations present challenges in fast-paced environments like sports medicine and outpatient rehab.
Recent advancements in dynamic pupillometry and smartphone-based technologies have brought renewed focus to the pupillary light reflex (PLR)—a fast, autonomic response that provides insight into brainstem and autonomic function. Emerging research now points to PLR metrics as reliable biomarkers for concussion, offering a quantifiable, physiologic measure to complement traditional concussion assessments.
Understanding the Pupillary Light Reflex in Concussion
The PLR describes the reflexive constriction and dilation of the pupils in response to light, driven by neural pathways involving the retina, midbrain, and autonomic nervous system. In healthy individuals, the reflex is rapid and symmetrical. In those with a mild traumatic brain injury (mTBI), subtle yet significant disruptions can occur. These include prolonged latency, reduced constriction velocity, and asymmetry—markers that may not be visible to the naked eye but are detectable through digital pupillometry.
Studies from Purdue University have demonstrated that individuals with mTBI exhibit both static and dynamic abnormalities in PLR, such as slower constriction speeds and smaller pupil diameters, indicating autonomic dysregulation and central nervous system involvement.
This aligns with broader findings from the Children’s Hospital of Philadelphia, where researchers have linked visio-vestibular impairments—including abnormal eye movements and light sensitivity—to prolonged recovery from concussion.
Clinical Evidence Supporting PLR Metrics
A 2023 study published by the JAMA Network assessed PLR responses in adolescent athletes with diagnosed concussions and compared them to age-matched controls. Out of nine measured PLR parameters—including maximum and minimum pupil diameter, latency, constriction velocity, and redilation time—eight showed statistically significant differences between concussed and non-concussed individuals.
These findings provide a foundation for using PLR measurements as objective, quantifiable data points during sideline assessments and follow-up visits. Particularly notable is the delayed constriction response and prolonged redilation time—both indicators of slowed autonomic recovery post-injury.
In further support of this application, a peer-reviewed study in Life demonstrated the accuracy in measuring PLR metrics and detecting concussion-related changes. The app's ability to detect subtle alterations in pupil dynamics provides clinicians with an accessible tool for decision-making across diverse care settings.
