Abstract
Purpose :
Light-induced tearing is a protective reflex associated with painful sensation of light, however, it is still unclear which light sensor provides input to this reflex. We hypothesized that light induced tearing is melanopsin-driven. This study tested this hypothesis by investigating the spectral characteristics and intensity-response function of light induced reflex tearing and its correlation with the melanopsin driven post-illumination pupil response (PIPR).
Methods :
11 visually normal participants completed the experiment, which consisted of 15 trials of 1-minute anesthetized Schirmer’s test on the right eye while pupil response was simultaneously recorded from the left eye using a video-based eye tracker. At 20 s of the trails, subjects receive either no light stimulation (baseline trial) or one flash of red (640±10 nm) or blue (467±17 nm) light stimuli of 400 ms duration presented to both eyes using a Ganzfeld stimulator. Light condition trials were presented in alternating fashion at 7 incremental steps of intensity (0.1, 1, 3.16, 10, 31.60, 100 and 400 cd/m2). PIPR was defined as the mean pupil diameter reduction from 10 to 30 s post illumination. Two-way repeated measures ANOVA and Pearson correlation coefficient were performed on tear production and PIPR data for statistical analysis.
Results :
Tear production in response to 10 to 400 cd/m2 blue light was significantly greater than baseline, and it increased steadily with increasing light intensity. Red light did not induce significant tear production until 400 cd/m2. There is a positive linear correlation between PIPR and tearing in response to blue light (R= 0.61, p<0.001) but not to red light (R=0.13, p=0.25).
Conclusions :
The intensity-response function and spectral characteristics of light-induced tearing are highly consistent with the features of melanopsin phototransduction. This finding is the first in-vivo evidence supporting the idea that light-induced tearing is mediated primarily by melanopsin photoactivity, which is a valuable insight into the mechanisms of photophobia.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.