Concussions and Pupil Testing: Are Eye Changes a Reliable Indicator of Brain Injury?
Pupillary assessments, whether through traditional light reflex testing or modern automated pupillometry, offer a non-invasive window into neurological function. But how reliable are these methods when it comes to diagnosing concussions or guiding return-to-play decisions?
Let’s explore the clinical relevance, research findings, and practical applications of pupil testing in concussion management.
The Neurological Basis: Why Pupil Changes Matter
The pupils are controlled by a balance between the parasympathetic and sympathetic nervous systems, with key involvement of the midbrain, particularly the Edinger-Westphal nucleus, which sends parasympathetic fibers to the pupil to mediate light reflexes (source). When a concussion occurs, mechanical forces can cause widespread neurological dysfunction, potentially impacting areas responsible for pupillary control.
Changes in pupil size, delayed light response, or asymmetry can reflect autonomic dysregulation, cranial nerve dysfunction, or increased intracranial pressure — all possible sequelae of brain trauma. As a result, assessing the pupillary light reflex (PLR) has long been part of neurological examinations in emergency and sports medicine settings.
However, subtle concussive injuries often produce nuanced or transient dysfunctions, making traditional flashlight tests potentially insufficient. Emerging tools like digital pupillometers now offer greater precision, quantifying aspects such as latency, constriction velocity, and dilation recovery. Research has shown that concussion-related impairments in the PLR can be objectively detected using these methods, supporting their value in clinical concussion assessment (source).
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Research Insights: Objective Measures vs. Traditional Methods
Recent research has helped illuminate the potential — and limitations — of pupil assessments for concussion evaluation. A 2024 study titled Examining Sport-Related Concussion Assessment and Management Techniques Among Athletic Training Preceptors Versus Non-Preceptors emphasized that pupillary evaluations, particularly using automated pupillometry, are becoming important adjuncts to traditional symptom checklists and balance tests (source).
The study highlighted that:
Preceptors, who often possess more advanced clinical experience, were significantly more likely to utilize pupillometry as part of their concussion protocols.
Pupillary assessments helped detect subtle neurological dysfunctions that standard symptom inventories could miss.
Automated measurements offered better reproducibility and reduced examiner bias compared to manual light tests.
Other investigations have echoed these findings. A study in The Journal of Neurotrauma demonstrated that concussion patients exhibited slower pupillary constriction and delayed dilation responses compared to controls, suggesting a direct link between mild traumatic brain injury (mTBI) and autonomic dysfunction.
Still, variability exists. Factors like ambient lighting, emotional arousal, medications, and pre-existing conditions (e.g., anisocoria, previous ocular trauma) can confound results. This makes it clear that while pupillary testing holds promise, it should not be used in isolation to confirm or exclude a concussion diagnosis.
Clinical Applications: Where Pupil Testing Fits in Practice
In the hands of trained clinicians, pupillary assessments can serve multiple roles in concussion management:
Initial Sideline Assessment: Immediate post-injury pupillary screening can help rule out serious conditions such as intracranial hemorrhage, especially if anisocoria or non-reactive pupils are observed. While rare in sport-related concussions, these findings necessitate urgent referral.
Ongoing Monitoring: Persistent or worsening pupillary abnormalities during recovery can signal complications such as evolving intracranial pathology or delayed autonomic recovery. Serial measurements with a pupillometer may offer a valuable, objective measure of progress or setback.
Return-to-Play Decisions: Although no single test should dictate clearance, incorporating quantitative pupillary metrics alongside symptom resolution, cognitive testing, and balance assessments provides a more complete clinical picture. Objective data can be particularly useful when athletes underreport symptoms to hasten return to play.
A clinical example:
A collegiate soccer player sustains a head injury during a match. Initial evaluation reveals normal neurological status except for slightly slowed pupillary constriction on the left eye. Symptom checklists and balance tests show minimal findings. Over the next week, automated pupillometry shows gradual normalization of constriction velocity and dilation time, mirroring symptom improvement. This additional objective measure reassures both clinician and athlete that recovery is progressing appropriately.
Current Limitations and Future Directions
Despite promising applications, several limitations must be acknowledged:
Normative Data Challenges: There remains a need for broader normative databases across different ages, ethnicities, and baseline autonomic profiles. Without robust comparisons, interpreting borderline findings can be difficult.
Lack of Standardization: Different devices use varied measurement protocols, leading to inconsistency across studies and clinical settings.
Contextual Interpretation Needed: Pupillary changes must be interpreted within the full clinical context, not as standalone indicators.
Emerging research is working to address these challenges. Advanced analytics, such as machine learning algorithms trained to detect abnormal pupillary patterns, may soon augment clinician interpretation. Longitudinal tracking tools may also allow for better individualized monitoring over an athlete’s career.
Additionally, studies are exploring how autonomic nervous system testing, including heart rate variability and pupil response combined, might offer a more sensitive multi-modal concussion detection strategy.
Practical Recommendations for Healthcare Providers
Based on current evidence, athletic trainers, physical therapists, and sports medicine clinicians should consider the following:
Incorporate pupillary assessments as part of a multi-modal evaluation strategy, alongside cognitive, balance, and symptom-based tests.
Prefer quantitative, automated pupillometry when available, especially for serial assessments.
Use pupillary findings to complement, not replace, clinical judgment.
Be aware of confounding variables like lighting conditions, medications, and baseline differences.
Educate athletes and coaches about the role of objective testing in promoting safe return-to-play decisions.
Ultimately, pupil testing provides a valuable tool — especially when used thoughtfully as part of a broader concussion management program.
Conclusion: A Promising Tool, Not a Silver Bullet
Pupillary changes offer a unique and clinically significant lens into neurological function following concussion. While traditional light reflex exams remain important, modern automated pupillometry enhances precision, reduces bias, and may uncover subtle dysfunctions missed by other tools.
Still, no single assessment can fully capture the complexity of concussion injuries. Integrating pupillary findings into a comprehensive evaluation strategy, alongside a keen understanding of each athlete’s baseline and context, represents the best path forward for optimizing safety, recovery, and long-term outcomes.
As the research base grows and technology continues to evolve, pupillary testing may well become an indispensable part of the concussion clinician’s toolkit — a development that holds promise for improving athlete care at every level.
