Abstract
BackgroundIn the human retina, the contribution of intrinsically photosensitive retinal ganglion cells (ipRGCs) to the regulation of the pupillary response remains poorly understood. The objective of the current study was to determine the response dynamics of the pupillary light reflex to short, successive pulses of light. In order to better assess the roles of ipRGCs and cones, we used pulses of blue and green light.MethodsEach participant was exposed to 1-ms blue (466 nm) and/or green (527 nm) light pulses simultaneously or separately, with inter-stimulus intervals (ISIs) of 0, 250, 500, 750, or 1000 ms. Pupil diameter was measured using an infrared camera system.ResultsWe found that human pupillary light responses during simultaneous irradiation or successive irradiation with ISIs ≤ 250 ms were equivalent, though successive irradiation of blue- and green-pulsed light with ISIs ≥ 500 ms induced markedly increased pupillary constriction.ConclusionsWe propose that this result may be related to cell hyperpolarization that occurs in the retina just after the first light stimulus is turned off, with the threshold for this effect being between 250 and 500 ms in the human retina.
Highlights
In the early part of this century, a novel type of photocell, the intrinsically photosensitive retinal ganglion cell, was discovered in the mammalian retina [1]
Our analyses showed that successive irradiation with pulses of blue and green light at inter-stimulus intervals (ISIs) ≥ 500 ms induced significantly greater pupillary constriction than did the other conditions (p < 0.05 or p < 0.01; Fig. 4)
McDougal and Gamlin [32] reported that the contribution of rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs) to the pupillary constriction was affected by the duration of a light stimulus
Summary
In the early part of this century, a novel type of photocell, the intrinsically photosensitive retinal ganglion cell (ipRGC), was discovered in the mammalian retina [1]. Researchers have suggested that input from cones and rods influences ipRGC response [4, 6, 10, 11, 21, 22]. IpRGCs as well as cones, rods, bipolar cells, amacrine cells, and ganglion cells in the retina are responsible for the pupillary light reflex [23]. Output from ipRGCs regulates the pupillary light reflex via the olivary pretectal nucleus in the pretectum [21]. The contribution of intrinsically photosensitive retinal ganglion cells (ipRGCs) to the regulation of the pupillary response remains poorly understood. In order to better assess the roles of ipRGCs and cones, we used pulses of blue and green light
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