Utility of Pupillary Light Reflex Metrics as a Physiologic Biomarker for Adolescent Sport-Related Concussion

Concussion diagnosis remains clinical, without objective diagnostic tests available for adolescents. Known deficits in visual accommodation and autonomic function after concussion make the pupillary light reflex (PLR) a promising target as an objective physiological biomarker for concussion.

To determine the potential utility of PLR metrics as physiological biomarkers for concussion.

Prospective cohort of adolescent athletes between ages 12 and 18 years recruited between August 1, 2017, and December 31, 2018. The study took place at a specialty concussion program and private suburban high school and included healthy control individuals (n = 134) and athletes with a diagnosis of sport-related concussion (SRC) (n = 98). Analysis was completed June 30, 2020.

Sports-related concussion and pupillometry assessments.

Pupillary light reflex metrics (maximum and minimum pupillary diameter, peak and average constriction/dilation velocity, percentage constriction, and time to 75% pupillary redilation [T75]).

Pupillary light reflex metrics of 134 healthy control individuals and 98 athletes with concussion were obtained a median of 12.0 days following injury (interquartile range [IQR], 5.0-18.0 days). Eight of 9 metrics were significantly greater among athletes with concussion after Bonferroni correction (maximum pupil diameter: 4.83 mm vs 4.01 mm; difference, 0.82; 99.44% CI, 0.53-1.11; minimum pupil diameter: 2.96 mm vs 2.63 mm; difference, 0.33; 99.4% CI, 0.18-0.48; percentage constriction: 38.23% vs 33.66%; difference, 4.57; 99.4% CI, 2.60-6.55; average constriction velocity: 3.08 mm/s vs 2.50 mm/s; difference, 0.58; 99.4% CI, 0.36-0.81; peak constriction velocity: 4.88 mm/s vs 3.91 mm/s; difference, 0.97; 99.4% CI, 0.63-1.31; average dilation velocity, 1.32 mm/s vs 1.22 mm/s; difference, 0.10; 99.4% CI, 0.00-0.20; peak dilation velocity: 1.83 mm/s vs 1.64 mm/s; difference, 0.19; 99.4% CI, 0.07-0.32; and T75: 1.81 seconds vs 1.51 seconds; difference, 0.30; 0.10-0.51). In exploratory analyses, sex-based differences were observed, with girls with concussion exhibiting longer T75 (1.96 seconds vs 1.63 seconds; difference, 0.33; 99.4% CI, 0.02-0.65). Among healthy control individuals, diminished PLR metrics (eg, smaller maximum pupil size 3.81 mm vs 4.22 mm; difference, -0.41; 99.4% CI, -0.77 to 0.05) were observed after exercise.

These findings suggest that enhancement of PLR metrics characterize acute adolescent concussion, while exercise produced smaller pupil sizes and overall slowing of PLR metrics, presumably associated with fatigue. Quantifiable measures of the PLR may serve in the future as objective physiologic biomarkers for concussion in the adolescent athlete.