Abstract
Introduction: The development of chromatic pupillometry has propelled significant advances in knowledge of the melanopsin-containing intrinsically photosensitive retinal ganglion cell (ipRGC) light detection pathway. Studies have used open-loop (stimulation of dilated eye and recording from fellow eye) and closed-loop (stimulation and recording of same eye) monocular paradigms to investigate pupil response dynamics; however it is not clear how intrinsic ipRGC signals from the two eyes are integrated. We investigated the binocular summation properties of the melanopsin-derived ipRGC signals using chromatic pupillometry. If the melanopsin system is summative, we hypothesized that there will be greater post-illumination pupillary response (PIPR) under binocular conditions when viewing melanopsin-active bright blue light. Methods: Pupillary responses were recorded with an eye tracker in 10 visually-normal participants. PIPR(10-25s post-illumination) was induced with full-field melanopsin-active blue light (470nm) and melanopsin-silent red light (635nm) stimuli at 60 cd/m2, presented for 400 ms with a Ganzfeld screen. Individual monocular responses were measured first (closed-loop paradigm) followed by binocular responses, 3 times on 3 separate days. To account for individual variability in pupil diameter, the pupil data was normalized to a 5s period before each stimulus (normalized pupil diameter = absolute pupil diameter/baseline pupil diameter). Results: Under blue light stimulation, PIPR responses were significantly greater for binocular than monocular viewing (p < 0.001), with a mean normalized difference of 0.13 (95% CI, 0.1-0.16), between viewing conditions. There was also a small but significant difference in PIPR between viewing conditions under red light stimulation (p = 0.01), with a mean normalized difference of 0.03 (95% CI, 0.01-0.05) between viewing conditions. Overall no effect of viewing eye was found on monocular trials. Conclusion: Melanopsin-mediated ipRGC signals are summated binocularly upstream of the retina. This evidence can be utilized to refine future protocols that target clinical populations, particularly those involving asymmetric ocular neuropathy.
Meeting abstract presented at VSS 2018