title: A five-primary photostimulator suitable for studying intrinsically photosensitive retinal ganglion cell functions in humans.
abstract: Intrinsically photosensitive retinal ganglion cells (ipRGCs) can respond to light directly through self-contained photopigment, melanopsin. IpRGCs also receive synaptic inputs from rods and cones. Thus, studying ipRGC functions requires a novel photostimulating method that can account for all of the photoreceptor inputs. Here, we introduced an inexpensive LED-based five-primary photostimulator that can control the excitations of rods, S-, M-, L-cones, and melanopsin-containing ipRGCs in humans at constant background photoreceptor excitation levels, a critical requirement for studying the adaptation behavior of ipRGCs with rod, cone, or melanopsin input. We described the theory and technical aspects (including optics, electronics, software, and calibration) of the five-primary photostimulator. Then we presented two preliminary studies using the photostimulator we have implemented to measure melanopsin-mediated pupil responses and temporal contrast sensitivity function (TCSF). The results showed that the S-cone input to pupil responses was antagonistic to the L-, M- or melanopsin inputs, consistent with an S-OFF and (L + M)-ON response property of primate ipRGCs (Dacey et al., 2005). In addition, the melanopsin-mediated TCSF had a distinctive pattern compared with L + M or S-cone mediated TCSF. Other than controlling individual photoreceptor excitation independently, the five-primary photostimulator has the flexibility in presenting stimuli modulating any combination of photoreceptor excitations, which allows researchers to study the mechanisms by which ipRGCs combine various photoreceptor inputs.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Dingcai
authors.initials: D
authors.lastname: Cao
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Nicandro
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Pablo A
authors.initials: PA
authors.lastname: Barrionuevo
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008027:Light; D008297:Male; D055254:Night Vision / Q000502:physiology; D010775:Photic Stimulation / Q000295:instrumentation*; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism / Q000528:radiation effects; D011680:Pupil / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000528:radiation effects*; D017299:Rod Opsins / Q000378:metabolism*; D055815:Young Adult; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin
keywords: five-primary photostimulator; ipRGC; melanopsin; photoreceptor; silent substitution