Assessment of ipRGC-Mediated Pupil Constriction in Photophobic Individuals with Traumatic Brain Injury

Title Assessment of ipRGC-Mediated Pupil Constriction in Photophobic Individuals with Traumatic Brain Injury
Author, Co-Author Phillip Yuhas, Patrick Shorter, Catherine McDaniel, Michael Earley, Andrew Hartwick
Topic
Year
2014
Day
Wednesday
Program Number
140025
Room
Room 205-207
Affiliation
Ohio State University College of Optometry
Abstract Purpose:  Photophobia is a common symptom in individuals who have suffered a 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 migraineurs. The goal of this work is to test the hypothesis that ipRGC function is altered in TBI patients with photophobia by assessing relative pupillary responses to blue and red light.

Methods:  Data was collected from 21 case subjects (mean age = 44.8±2.5; 52% female) with a prior TBI and self-reported photophobia, along with 11 control subjects (mean age = 40.6±4.4; 64% female). The subjects’ left eyes were dilated with 0.5% tropicamide. After a 10 min dark adaptation period, light stimuli were generated by blue (465 nm, 1x1013 phots/s/cm2) and red (635 nm, 7x1013 phots/s/cm2) LEDs. Each stimulus flashed on and off at 0.1 Hz for 30s and was delivered to the left eye while the right pupil was recorded. The amplitude of normalized pupil fluctuation was quantified using Fourier fast transforms.

Results: As ipRGCs continue to fire after light offset, smaller values of the Fourier-derived pupil fluctuation are indicative of greater ipRGC contribution to the pupil responses.  In either the case or the control group, the Fourier-derived pupil fluctuation was significantly (P=0.004 and P=0.004, respectively) less for the blue (25.4±6.6 [SD], 23.8±2.4) versus red light (28.4±5.6, 28.1±3.1). There was no significant difference in pupil fluctuation elicited by the blue (P=0.5) or red light (P=0.8) when the data for the case and control subjects were compared. However, case subjects displayed greater variability in their pupil responses, especially to blue stimuli.

Conclusion: Similar to control subjects, case subjects showed robust ipRGC-mediated components in their pupil responses to blue light. Using this metric, ipRGC light sensitivity does not seem to be altered in individuals with TBI-associated photophobia. However, greater pupil response variability in the case subjects suggests that ipRGC function may be more heterogeneous in this group.
Affiliation of Co-Authors The Ohio State University College of Optometry, The Ohio State University College of Optometry, The Ohio State University College of Optometry, The Ohio State University College of Optometry
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