A five-primary photostimulator suitable for studying intrinsically photosensitive retinal ganglion cell functions in humans

Jan 28, 2015Journal of vision

A five-color light device for studying special light-sensitive eye cells in humans

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Abstract

An LED-based five-primary photostimulator can independently control excitations of rods, S-, M-, L-cones, and melanopsin-containing ipRGCs.

The photostimulator maintains constant background excitation levels, essential for studying ipRGC adaptation behavior.
Preliminary studies demonstrated that S-cone input to pupil responses is antagonistic to L-, M-, and melanopsin inputs.
Melanopsin-mediated temporal contrast sensitivity function (TCSF) displayed a distinct pattern compared to L + M or S-cone mediated TCSF.
This tool allows for the modulation of any combination of photoreceptor excitations, facilitating the study of ipRGC input mechanisms.

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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.

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A five-primary photostimulator suitable for studying intrinsically photosensitive retinal ganglion cell functions in humans

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