Correlation Between Accommodative Facility and Light-Evoked Pupil Responses in Individuals with History of Mild...

Previous studies have shown those with a history of a traumatic brain injury (TBI) have altered pupillary light responses compared with those without a history of TBI. Those with a history of TBI are also more likely to have accommodative deficits. We investigated the relationship between light-evoked pupil dynamics and accommodative function in individuals who have previously experienced a TBI.

A total of 17 participants with a history of mild TBI were recruited. Pupil metrics were measured using a commercial pupillometer and included baseline diameter, latency, constriction amplitude, average constriction velocity, peak constriction velocity and peak dilation velocity. Accommodative function was assessed using clinical measurements of facility and amplitude. Pupil metrics were compared among those with versus without accommodative dysfunction.

One-way ANCOVA testing (controlling for age and time since most recent TBI) comparing groups with and without accommodative dysfunction showed that those with accommodative dysfunction had significantly larger light-evoked pupil constriction amplitudes (p = 0.037) and significantly faster average constriction velocity (p = 0.007) compared with those without accommodative dysfunction. No significant differences were observed for other pupil metrics (p > 0.05 for all). ANCOVA testing (controlling for age and time since TBI) to determine whether decreased amplitude of accommodation or facility was more strongly related to the differences in pupil metrics observed between those with versus without accommodative dysfunction, showed significantly larger light-evoked pupil constriction amplitudes (p = 0.007) and significantly faster average constriction velocity (p = 0.002) among those with reduced accommodative facility compared with those with normal accommodative facility. No statistically significant differences were observed between those with reduced versus normal accommodative amplitude (p ≥ 0.07). Among all participants, monocular accommodative facility measures were significantly correlated with greater pupil constriction amplitude (right eye: rho = -0.721, p = 0.001; left eye: rho = -0.65, p = 0.005), and greater average constriction velocity (right eye: rho = -0.58, p = 0.015; left eye: rho = -0.57, p = 0.016).

The results of this small-sample study suggest that accommodative function and light-evoked pupillary dynamics are correlated in individuals with a history of TBI. Those with accommodative dysfunction showed greater pupil constriction amplitudes and velocities and this relationship may reflect shared autonomic or oculomotor mechanisms.