ISOLATION OF IPRGC CONTRIBUTION TO THE HUMAN PUPILLARY LIGHT REFLEX

Title ISOLATION OF IPRGC CONTRIBUTION TO THE HUMAN PUPILLARY LIGHT REFLEX
Author, Co-Author Phillip Yuhas, Holly Moose, Andrew Hartwick
Topic
Year
2012
Day
Wednesday
Program Number
120153
Room
Room 225 A-B
Affiliation
The Ohio State University, College of Optometry
Abstract PURPOSE: Intrinsically photosensitive retinal ganglion cells (ipRGCs), which express melanopsin photopigment, respond sluggishly to light and are thought to contribute to the sustained pupillary constriction that occurs after the offset of a bright stimulus. Due to the unique temporal properties of these ganglion cell photoreceptors, our aim was to utilize flickering light stimuli to isolate an ipRGC component to the human pupillary light reflex (PLR).

METHODS: A flickering LED light stimulus was presented to the dilated left eye of 18 healthy subjects (age: 23 to 27). The consensual pupil response was recorded in the right eye under infrared illumination. The amplitude of the flicker in the pupil response (% of maximum pupil constriction) was determined using Fourier analysis. The effect of stimulus frequency (range: 0.05 to 1.00 Hz), intensity (range: 1012 to 1015 phots/s/cm2), and prior light exposure on the pupil response to flickering red (625 nm) and blue (470 nm) light was determined.

RESULTS: In response to a slowly flickering (0.1 Hz) stimulus, there was a significant reduction in magnitude of pupil flicker elicted by the blue versus red light as the intensity increased to 1014 phots/s/cm2 (14.0% vs 21.7%; p<0.01). For flickering stimuli at 1014 phots/s/cm2, there was a significant difference (P<0.05) in the pupil response elicited by the two stimuli (blue vs. red) when presented at 0.2, 0.1 and 0.05 Hz, but not at 0.5 or 1.0 Hz, flicker frequencies. Unexpectedly, the flicker in the pupil response to flashing (0.1 Hz) bright (1014phots/s/cm2) red light significantly decreased when the red light was alternated with flashes of blue light (16.1% ± 1.9 SEM) as compared to the flickering stimuli of red light alone (22.2% ± 1.4 SEM).

CONCLUSIONS: The ipRGC input to the PLR can be best isolated with a bright, slowly flickering, stimulus that alternates between long and short wavelengths.

ADDITIONAL COMMENTS: Funded by NIH T35 Grant EY007151, Optometric Educators Inc., Ohio Lions Eye Research Fund.
Affiliation of Co-Authors The Ohio State University, College of Optometry, The Ohio State University, College of Optometry
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