Abstract
Primate vision starts with the activation of rod photoreceptors in dim light and short (S)-, medium (M)-, and long (L)- wavelength sensitive cone photoreceptors in daylight. A parallel, non-rod, non-cone photoreceptive pathway, arising from a unique population of melanopsin-expressing, intrinsically-photosensitive retinal ganglion cells (ipRGCs), has been demonstrated in mammals including primates. Our understanding of the anatomy, physiology, and behavioral roles of primate ipRGCs has improved substantially over the past decade. In primates, this anatomically distinct population of ipRGCs is strongly activated by rods and cones, and the intrinsic light response combines with rod and (L + M) cone-derived responses to signal irradiance over the full dynamic range of primate vision. Each of these component ipRGC light responses has distinct spectral and temporal attributes that can be characterized both in vitro and in vivo. Further, in primates including humans, we have demonstrated that these cells play an important role both in light-evoked pupillary responses as well as in the sustained pupil constriction that occurs after bright light cessation – the post-illumination pupil response. The post-illumination pupil response is driven by the intrinsic photoresponse of ipRGCs, and can be used to evaluate ipRGC activity in normal and diseased retinas.