Comparison of pupillary dynamics to light in the mild traumatic brain injury (mTBI) and normal populations

Abstract

Purpose: To determine if mTBI adversely affects the pupillary light reflex (PLR).

Methods: The PLR was evaluated in mTBI and compared to normal individuals under a range of test conditions. Nine pupil parameters (maximum, minimum and final pupil diameter, latency, amplitude and peak and average constriction and dilation velocities) and six stimulus conditions (dim pulse, dim step, bright pulse, bright step, bright red step and bright blue step) were assessed in 32 adults with mTBI (21–60 years of age) and compared to 40 normal (22–56 years of age). The Neuroptics, infrared, DP-2000 binocular pupillometer was used (30 Hz sampling rate; 0.05 mm resolution) with binocular stimulation and recording.

Results: Different test conditions allowed for discrimination of different parameters. For any of the given six test conditions, five-to-eight of the nine pupillary parameters were statistically different (p < 0.05) between the two diagnostic groups. The most promising parameters for diagnostic differentiation were constriction latency, all pupillary diameters, average constriction velocity and peak dilation velocity.

Conclusions: MTBI adversely affects the PLR. This suggests an impairment of the autonomic nervous system. The findings suggest the potential for quantitative pupillary dynamics to serve as an objective mTBI biomarker.

Keywords:

• Mild traumatic brain injury (mTBI)
• pupillometry
• pupil light reflex
• visual biomarker
• parasympathetic system
• sympathetic system

Acknowledgements

We thank Dr. Neera Kapoor for her assistance in organizing and recruiting subjects for our study and Dr. Naveen K. Yadav for his technical and statistical advice during manuscript preparation. We thank the United States Army Aeromedical Research Laboratory for their generous loan of the Neuroptics DP-2000 binocular pupillometer used in this research. Also, we appreciate the insightful comments of Dr. Gilmartin Bernard and Dr. Randy Kardon related to the research endeavour.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.