Some normal modes of an infinite hexagonal array of identical circular dielectric rods

Photoreceptor waveguides and effective retinal image quality

“…1 At a retinal level there are factors other than sampling, however, that may affect the visual sensation produced. Of particular interest is that the photoreceptors are known to guide light, [2][3][4][5] and this guiding mechanism may influence the amount as well as the spectrum of light that reach the visual pigments contained in the outer segments. Indeed, waveguide properties of individual photoreceptors can explain a reduced visual impact of light rays entering the eye near the rim of its pupil as well as of intraocularly scattered light in what is known as the Stiles-Crawford effect of the first kind (SCE).…”

27. A ging and the eye’s optics

“…In doing so approximations have to be made regarding the exact geometrical shape and refractive index distribution across the photoreceptor and its surrounding medium, while the electromagnetic coupling between neighboring photoreceptors has typically been ignored despite of their tight cellular packing. The waveguide modes for a hexagonal arrangement of cylindrical waveguides representative of the cone photoreceptor mosaic has slow modes confined to each cylindrical waveguide (resembling the modes of an isolated waveguide) and faster modes confined to the space between the waveguides [78,79]. Accurate measurement of refractive indices in photoreceptors is challenging, and some variations exist in published values, but they generally find a higher refractive index of the outer than the inner segment [80].…”