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Vision Res. 2016 Jul;124:59-65. doi: 10.1016/j.visres.2016.06.010. Epub 2016 Jul 6.

The absence of attenuating effect of red light exposure on pre-existing melanopsin-driven post-illumination pupil response.

Author information

1
Program in Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Canada.
2
Program in Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Canada; Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Canada.
3
Program in Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Canada; Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, Canada; Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Canada. Electronic address: agnes.wong@sickkids.ca.

Abstract

It has been proposed that after activation by blue light, activated melanopsin is converted back to its resting state by long wavelength red light exposure, a putative mechanism of melanopsin chromophore recovery in vivo. We tested this hypothesis by investigating whether red light attenuates the ongoing post-illumination pupil response (PIPR) induced by melanopsin-activating blue light. Pupillary light responses were tested using "Blue+Red" double flashes and "Blue Only" single flash stimuli in 10 visually normal subjects. For "Blue+Red" conditions, PIPR was induced with an intense blue flash, followed by experimental red light exposure of variable intensity and duration (Experiment 1) immediately or 9s after the offset of the blue flash (Experiment 2). For "Blue Only" conditions, only the PIPR-inducing blue stimuli were presented (reference condition). PIPR was defined as the mean pupil size from 10 to 30s (Experiment 1) and from 25 to 60s (Experiment 2) after the offset of blue light stimuli. The results showed that PIPR from "Blue+Red" conditions did not differ significantly from those of "Blue Only" conditions (p=0.55) in Experiment 1. The two stimulation conditions also did not differ in Experiment 2 (p=0.38). We therefore conclude that red light exposure does not alter the time course of PIPR induced by blue light. This finding does not support the hypothesis that long wavelength red light reverses activated melanopsin; rather it lends support to the hypothesis that the wavelengths of stimuli driving both the forward and backward reactions of melanopsin may be similar.

KEYWORDS:

Chromatic pupillometry; Melanopsin; Post-illumination pupil response; Pupil light reflex

PMID:
27371765
DOI:
10.1016/j.visres.2016.06.010
[Indexed for MEDLINE]
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