Quantifying pupillary asymmetry through objective binocular pupillometry in the normal and mild traumatic brain injury (mTBI) populations

Introduction: Little is known about human inter-ocular pupillary asymmetry (IOPA). Thus, the purpose of the present investigation was to assess objectively static and dynamic IOPA in normals and in individuals with mild traumatic brain injury (mTBI).Methods: The pupillary light reflex (PLR) was assessed in an adult population of normals and in those with mTBI using the Neuroptics DP-2000 binocular pupillometer. Four stimulus conditions were used to optimize the assessment. Two aspects of the pupil were assessed: baseline diameter prior to light stimulation and the dynamic amplitude of constriction following light stimulation.Results: There was no statistical difference in either the static or dynamic IOPA between the two groups. Thus, the data were combined for a better global parameter estimate. The mean average static IOPA was 0.26 mm (SD = 0.20 mm) or 4.17% (+/- 3.29%). The mean average dynamic IOPA was dependent on the light stimulus condition, with the average across all four test conditions being 0.11 mm (+/- 0.10 mm) or 1.84% (+/- 1.70%).Discussion: The inter-ocular pupillary effects of mTBI appear to be symmetrical rather than asymmetrical in nature. The findings provide clinicians and researchers a useful quantitative guideline to assess normal vs abnormal static and dynamic inter-ocular pupillary asymmetry (IOPA) in these two populations.