Melanopsin-mediated post-illumination pupil response in the peripheral retina

Jun 9, 2016Journal of vision

Pupil response after light exposure controlled by light-sensing cells in the outer retina

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Abstract

Pupil constriction amplitude was similar in both central and peripheral retina regions.

The time to minimum pupil diameter increased with higher melanopsin excitation.
Peripheral post-illumination pupil response (PIPR) followed a corneal flux density relationship but exhibited lower amplitude than at the fovea.
Differences in the spatial and temporal characteristics of light responses suggest distinct roles for extrinsic and intrinsic inputs in pupil control for central and peripheral areas.
The observed eccentricity-dependent change in PIPR amplitude may relate to the hill of vision in visual testing.
These findings could inform the development of pupil perimetry techniques to assess PIPR in specific visual field regions.

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Intrinsically photosensitive retinal ganglion cells (ipRGCs) regulate pupil size by integrating extrinsic rod and cone signals with intrinsic melanopsin-mediated phototransduction. Light adapted pupil diameter is determined by the corneal flux density (CFD), and for central visual field stimulation the melanopsin-mediated post-illumination pupil response (PIPR) follows this same CFD relationship. Rods, cones, and ipRGCs vary in size, density, and distribution across the retina, but how these differences affect the amplitude and timing of the extrinsic and intrinsic pupil light reflex in the central and peripheral retina is unknown. We determined the relationship between stimulus area and photon flux with stimuli constant for CFD, irradiance, or area at central (0°) and peripheral (20°) eccentricities with high and low melanopsin excitation. We show that the pupil constriction amplitude was similar at both eccentricities and the time to minimum diameter increased as melanopsin excitation increased. In contrast, the peripheral PIPR follows a CFD relationship but with lower amplitude compared with that at the fovea. This indicates differences in the spatial and temporal characteristics of extrinsic and intrinsic ipRGC inputs to the pupil control pathway for the central and peripheral retina. The eccentricity-dependent change in PIPR amplitude may be analogous to the hill of vision observed in visual perimetry; such knowledge is an important precursor to the development of pupil perimetry paradigms to measure the PIPR in select regions of the visual field.

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Melanopsin-mediated post-illumination pupil response in the peripheral retina

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