Abstract
The human pupillary light response is driven by all classes of photoreceptors in the human eye—the three classes of cones, the rods, and the intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin. These photoreceptor classes have distinct but overlapping spectral tuning, and even a monochromatic light with a wavelength matched to the peak spectral sensitivity of a given photoreceptor will stimulate all photoreceptors. The method of silent substitution uses pairs of lights (“metamers”) to selectively stimulate a given class of photoreceptors while keeping the activation of all others constant. In this primer, we describe the method of silent substitution and provide an overview of studies that have used it to examine inputs to the human pupillary light response.
Highlights
At the input level, the size of the pupil is controlled by the activity of the different photoreceptors in the human eye [1]
Photoreception in the human retina is based on the signals produced by the three types of cones—the long[L]-wavelength-sensitive cones, the medium[M]-wavelength-sensitive cones, and the short[S]-wavelength-sensitive cones, the rods, and the intrinsically photosensitive retinal ganglion cells, which contain the photopigment melanopsin [2,3,4,5,6]. ipRGCs receive synaptic input from cones and rods but, in the absence of those inputs, these cells themselves are photosensitive due to the expression of the melanopsin photopigment in the cell membrane
An important desideratum for examining how the different photoreceptors contribute to the human pupillary light response is that stimuli produce responses specific to a given photoreceptor class
Summary
The size of the pupil is controlled by the activity of the different photoreceptors in the human eye [1]. All light that reaches the retina is filtered by the lens and ocular media [7], thereby shifting the effective spectral sensitivity This pre-receptoral filtering is accounted for in the spectral sensitivities for cones, rods, and melanopsin-containing ipRGCs. An important desideratum for examining how the different photoreceptors contribute to the human pupillary light response is that stimuli produce responses specific to a given photoreceptor class. Because photoreceptors weight input light by their spectral sensitivity function, in the case of two photoreceptors, it is possible to find two lights and scale them such that the excitation of one of the photoreceptors remains constant in this wavelength exchange, while the other one “sees” a difference This is shown in Figure 1D: The peak emissions of lights E1 and E2 have been chosen to match the two 50% points of the S-cone spectral sensitivity, thereby eliciting the same responses. The same principle can be extended to more than two photoreceptors
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
