Pupillary responses to light in chronic non-blast-induced mTBI

Abstract

Purpose: To evaluate objectively and quantitatively human pupillary responses to a light stimulus under photopic conditions in individuals with non-blast-induced, chronic, mild traumatic brain injury (mTBI).

Methods: Seventeen individuals with chronic, non-blast-induced mTBI and 15 visually-normal (VN) controls were tested (aged 21–45 years). Pupillary responsivity to a brief step-input light stimulus was assessed objectively in each eye for 5 seconds using the Neuroptics PLR-200 monocular, hand-held pupillometer with its pre-set and automated eight parameter analysis.

Results: Five of the eight parameters assessed were significantly reduced (p ≤ 0.05) in the mTBI group as compared to the VN control group: maximum (or peak) constriction velocity, average constriction velocity, average dilation velocity, maximum diameter and amplitude of constriction. The remaining three parameters were similar in each group (p > 0.05): constriction latency, 75% dilation recovery time and minimum diameter.

Conclusions: The slowed dilation dynamics and reduced maximum pupillary diameter in mTBI suggest deficiency primarily of the sympathetic control system. The reduced peak velocities and related amplitudes suggest subtle parasympathetic involvement.

• Mild traumatic brain injury
• parasympathetic system
• pupillary dynamics
• pupillary light reaction
• sympathetic system

Acknowledgements

The authors thank Dr. Jose E. Capo-Aponte (Womack Army Medical Center, Fort Bragg) for providing us with the instrumentation. We also thank LTC James Troung for his helpful discussion.

Declaration of interest

This project was funded by the SUNY College of Optometry’s Schnurmacher Institute for Vision Research. The authors report non conflicts of interest. The authors alone are responsible for the content and writing of the paper.