Photoreceptor-Directed Contrast Modulation Flicker Perimetry Using the Silent Substitution Technique

Purpose: The silent substitution principle enables a selective modulation of individual photoreceptor classes while maintaining constant excitation of all others. We describe a five-primary video projector and present pilot photoreceptor-directed contrast modulation flicker perimetry data from four normal observers. Methods: The Multi-Channel Visual Stimulator (MCVS; Cambridge Research Systems Limited, Rochester, UK) is a projector that uses a digital micromirror device to create images based on the emission from five primaries (red, amber, green, blue, and deep blue) that are driven by pulse-width modulation. L-, M-, and S-cone-directed circular stimuli (0.86) were presented at the central locations of the 10-2 pattern (±8° horizontally, ±6° vertically). The photoreceptor excitation was modulated sinusoidally around the background at temporal frequencies of 2 Hz and 20 Hz. Four normal observers (two male, two female; aged 35, 37, 47, and 65 years) were tested. Results: Temporal contrast sensitivities showed expected photoreceptor pathway characteristics, comparable with earlier experiments using a larger, annular test field. Specifically, L- and M-cone-driven sensitivities were very similar at 2 Hz (red-green opponent pathway), but L-cone-driven sensitivities were higher than M-cone-driven sensitivities at 20 Hz (luminance pathway). S-cone-driven sensitivities were lower near fixation but decreased less toward the periphery. Conclusions: The MCVS enables spatial mapping of photoreceptor-directed temporal contrast sensitivities across the central retina. This approach facilitates pathway-specific investigation of retinal processing and holds promise as a functional outcome measure in clinical trials targeting neuroretinal disorders. Translational Relevance: Photoreceptor-directed perimetry may provide sensitive outcome measures for neuroretinal disease diagnosis and clinical trials.