|Title||CORRELATION OF OBSERVER-GRADED LIGHT SENSITIVITY TO PUPIL RESPONSES IN HEALTHY SUBJECTS STIMULATED WITH RED AND BLUE FLICKERING LIGHT|
|Author, Co-Author||Phillip Yuhas, Patrick Shorter, Catherine McDaniel, Michael Earley, Andrew Hartwick|
Photophobia is a common symptom associated with traumatic brain injury and migraine. Recent evidence has implicated blue light-sensitive intrinsically photosensitive retinal ganglion cells (ipRGCs) in contributing to the neural circuitry mediating increased light sensitivity in migraine sufferers. This study's purpose was to: 1) develop a grading protocol for assessing light sensitivity using digital recordings; and 2) determine whether these gradings correlate to differences in the pupil responses to flickering red and blue light stimuli.
19 subjects (ages 23-27) were monocularly stimulated with bright(~1014 phots/s/cm2), slowly (0.1 Hz) flickering red and blue light while the contralateral eyes were digitally recorded. The difference in the pupil constriction fluctuation elicited by the red versus blue flickering light was determined with Fourier analysis. Using a 5-point scale, 5 masked observers graded the signs of light sensitivity (i.e. blinking, squinting, tearing) exhibited by the subjects in response to the two colored light stimuli.
Pupillary fluctuation was significantly less in response to the blue light (15.4% ± 0.9 SE), compared to the red light (22.7% ± 1.0 SE), consistent with an increased contribution of ipRGCs. The observers’ gradings of light sensitivity were in good agreement (ICC = 0.74). Also, the gradings were significantly (P=0.007) higher in response to the blue light stimuli (2.79 ± 0.11) compared to the red light stimuli (2.54 ± 0.13). A significant correlation (R=0.61) was found between the pupil responses and the gradings; subjects with a greater difference in response to the blue versus red flickering light were more likely to exhibit less signs of light sensitivity.
Signs of light sensitivity in healthy subjects can be graded with good inter-observer agreement. This data can be developed into a standardized grading system. Surprisingly, subjects who showed smaller differences in their pupil response to red versus blue light (indicative of more minor ipRGC contributions) exhibited greater observer-graded signs of light sensitivity.
Department of Defense TATRC Grant W81XWH-12-1-0434
|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|