Leakage of Light and its relation to the Stiles-Crawford Effects of the First and Second Kind using an Array of Cylindrical Absorbers as Retinal Phantom.

Abstract

Purpose : There is evidence that the psychophysical Stiles-Crawford effects (i.e., SCE-I and SCE-II) relate to absorption and leakage of light from the outer segments of cone photoreceptors (Vohnsen et al., J. Vision 2017, Vol. 17: 18). The aim of this study is to perform a detailed analysis of absorption using a macroscopic model of the photoreceptor outer segments and relate the findings to the visibility distribution of the SCE-I and SCE-II hue shift for oblique light at selected wavelengths.

Methods : A hexagonal array of 7 liquid-filled test tubes is used as a ×10³ upscaled model of foveal photoreceptor outer segments. Blue, green, and red food dyes (Dr. Oetker^TM) are used to model absorption resembling that of visual pigments. The array is illuminated with white light from a tungsten-halogen source via a liquid-filled bandpass filter (Meadowlark^TM). The visibility changes, and the shift of the spectral peak at oblique incidence is determined at 5 discrete wavelengths from 450 to 650 nm using a fiber-guided spectrometer (OceanOptics^TM) as well as a color CCD camera (Thorlabs^TM). The findings are compared to those obtained in the right eye of three emmetropic subjects (22, 25 and 54 years) with a modified uniaxial SCE-I and SCE-II characterization system across a 2-degrees visual angle with a digital micromirror device (Carmichael Martins & Vohnsen, OPO 2018, Vol. 38).

Results : The modeling shows that absorption approximates that of the SCE-I with a characteristic directionality parameter determined by the test tube geometry and the leakage of oblique light. The findings are fitted to those of a Gaussian SCE-I and to that of a ray absorption model as a function of angle of incidence. We find directionality parameters in the 0.03/mm² to 0.10/mm² range when rescaled to a schematic eye of axial length 22.2 mm. The SCE-II is determined by a central wavelength shift for oblique angles of incidence when brightness has been adjusted for the SCE-I.

Conclusions : We find that the SCE-I and SCE-II can be effectively modeled at the macroscopic scale with an array of absorbers representing photoreceptor pigments. The model builds on earlier studies with waveguide arrays and photonic crystal fibers. The directionality parameter approximates that of the human subjects determined psychophysically and is consistent with the wavelength dependence of the SCE-II.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.