Research Reports - Blue and red light-evoked pupil responses in photophobic subjects with TBI
Optom Vis Sci. 2017 Jan;94(1):108-117. doi: 10.1097/OPX.0000000000000934.
Yuhas PT(1), Shorter PD, McDaniel CE, Earley MJ, Hartwick AT.
PURPOSE: Photophobia is a common symptom in individuals suffering from traumatic
brain injury (TBI). Recent evidence has implicated blue light-sensitive
intrinsically photosensitive retinal ganglion cells (ipRGCs) in contributing to
the neural circuitry mediating photophobia in migraine sufferers. The goal of
this work is to test the hypothesis that ipRGC function is altered in TBI
patients with photophobia by assessing pupillary responses to blue and red light.
METHODS: Twenty-four case participants (mean age 43.3; 58% female), with mild TBI
and self-reported photophobia, and 12 control participants (mean age 42.6; 58%
female) were in this study. After 10 minutes of dark adaptation, blue (470 nm, 1
× 10 phots/s/cm) and red (625 nm, 7 × 10 phots/s/cm) flashing (0.1 Hz) light
stimuli were delivered for 30 seconds to the dilated left eye while the right
pupil was recorded. The amplitude of normalized pupil fluctuation (constriction
and dilation) was quantified using Fourier fast transforms.
RESULTS: In both case and control participants, the amplitude of pupil
fluctuation was significantly less for the blue light stimuli as compared to the
red light stimuli, consistent with a contribution of ipRGCs to these pupil
responses. There was no significant difference in the mean pupil fluctuation
amplitudes between the two participant groups, but case participants displayed
greater variability in their pupil responses to the blue stimulus.
CONCLUSIONS: Case and control participants showed robust ipRGC-mediated
components in their pupil responses to blue light. The results did not support
the hypothesis that ipRGCs are "hypersensitive" to light in TBI participants with
photophobia. However, greater pupil response variability in the case subjects
suggests that ipRGC function may be more heterogeneous in this group.