Guided light and diffraction model of human-eye photoreceptors

Abstract

The photoreceptors of the living human eye are known to exhibit waveguide-characteristic features. This is evidenced by the Stiles-Crawford effect observed for light incident near the pupil rim, and by the directional component of light reflected off the retina in the related optical Stiles-Crawford effect. We describe a model for the coupling of light to/from photoreceptors on the basis of waveguide theory that includes diffraction between the eye pupil and the photoreceptor apertures, and we show that valuable insight can be gained from a Gaussian approximation to the mode field. We apply this knowledge to a detailed study of the relationship between the Stiles-Crawford effect and its optical counterpart.

Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision

“…An initial light distribution entering the cell was taken as a diffraction pattern from the eye's pupil, which is broadened by corneal aberrations, to create an average Gaussian distribution of B40 mm width 24,25 . Next, the field was propagated down the medium, plane by plane, where every step was of 0.13 mm length.…”

“…The refractive indices of Müller cells are higher than those of their surrounding throughout the retina's depth 10,11 and therefore the cells can be regarded as natural optical fibres 17,23,24 . The refractive index profile and the cell's structure determine the efficiency of light guiding for the various wavelengths.…”

Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography

“…Two leading views are that the waveguided light originates from (1) reflections across the entire axial length of the outer segment due to refractive index variations induced by the stack of photopigment carrying discs [20] and (2) reflections from the posterior tips of the photoreceptor outer segments (PTOS) and possibly from melanin granules of the RPE [21][22][23]. A third view has been suggested recently in that light reflecting from layers further behind the photoreceptors is also waveguided, especially at longer wavelengths [24].…”

The Dependence of Spatial Distribution of Excitement of Receptors on Their Stiles-Crawford Effect

“…The obliquity of the Poynting vectors somehow kills the interference effect in the retinal plane owing to rapid and irregular phase fluctuations in the incoherent illumination [6]. With the disappearance of the interference effect the SCE I brightness reduction for oblique incidence reappears [7]. This also excludes hitherto widely used and implemented effective shading of the wavefront amplitude before interference [8][9][10][11][12][13] as a possible explanation for SCE I.…”