Red light-mediated photopotentiation of pupillary light responses

Title Red light-mediated photopotentiation of pupillary light responses
Author, Co-Author Phillip Yuhas, Andrew Hartwick
Topic Functional Vision/Pediatrics
Program Number
211 AB
The Ohio State University College of Optometry

Purpose: Emerging evidence indicates that prior light exposure influences pupillary light responses (PLR). In this work, we characterized the change in pupil constriction induced by repeated exposure to red and blue light flashes.

Methods: 6 subjects (age 28.5 ± 2.6) participated in one session involving 3 pupil tests. Each 2 min-long test consisted of bright (1013 phots/s/cm2), flickering (0.1 Hz) stimuli of either only red (RED; 625 nm), only blue (BLUE; 470 nm), or red-blue alternating (ALT) light. After 20 min dark adaptation, the stimuli were presented to the dilated left eye and the consensual pupil response was recorded. Overall pupil constriction (normalized; 0% = max dilation, 100% = max constriction) and photopotentiation (change in light-evoked pupil constriction over duration of the test) were calculated.

Results: The mean overall pupil constriction was significantly greater (p = 0.04) during the ALT test (69.6% ± 1.6) than during the RED test (64.4% ± 1.2). There were no differences (p > 0.05) in total mean constriction between the ALT and BLUE (67.2% ± 1.4) or RED and BLUE tests. Significant PLR photopotentiation was detected in the RED test (5.1% ± 1.8; p = 0.03), but not in the BLUE test (0.9% ± 3.2; p > 0.05). However, there was significant PLR photopotentiation to blue light during the ALT test (8.8% ± 3.25; p = 0.05), indicating that the intervening exposure to red light during this test altered the blue light-evoked pupil responses.

Conclusion: These results indicate that exposure to red light potentiates (enhances) subsequent pupil responses to either red or blue light. We propose that this phenomenon reflects an alteration in the light responses of intrinsically photosensitive retinal ganglion cells (ipRGCs) through either intrinsic (i.e. regeneration of melanopsin photopigment within ipRGCs) or extrinsic (i.e. modification of ipRGCs by retinal neuromodulators) mechanisms.

Affiliation of Co-Authors The Ohio State University College of Optometry