Replication and Expansion of Pupillary Light Reflex as Diagnostic Mild Traumatic Brain Injury Tool in Military Cadets

Pupillometers can quantitate an individual's pupillary light reflex (PLR), which involves a complex interaction between the sympathetic and parasympathetic nervous systems. Growing evidence suggests that mild traumatic brain injury (mTBI) impairs the regulatory processes that balance sympathetic and parasympathetic nervous system responses; therefore, the PLR may serve as a diagnostic mTBI biomarker. Preliminary evidence in this area would be enhanced by replication.

One hundred and ninety-six US Military Academy cadets completed standard concussion assessments (Standardized Assessment of Concussion, Sport Concussion Assessment Tool-5, and Balance Error Scoring System) during accession for preinjury baseline and post-mTBI within 48 hours, when they were asymptomatic, and when they were cleared for unrestricted return to activity. At each of these time points, a handheld pupillometer was used to assess pupillary light reflex in both eyes consecutively.

PLR metrics that showed significant disruption (larger change, longer time, and faster velocity) at injury (T1) compared with baseline (T0) included overall diameter change (End-Initial_Diam, P < .001), the percent of pupil constriction (Constriction%, P < .01), the time for the pupil to return to 75% of its starting size (T75, P < .05), and the maximum constriction velocity (Max_Constrict_Velocity, P < .001). Average dilation velocity was not significantly different immediately after injury (T1) but was disrupted (faster velocity) at the asymptomatic time point (T2, Dilat_Velocity, P < .001) and was no longer statistically different from baseline at unrestricted return to activity (T3, P > .5).

We were able to replicate the use of several PLR metrics as a biomarker for mTBI diagnosis that could easily be included with standard clinical measures.