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Jean-Marie Gorrand, Michel Doly; Optical Stiles-Crawford Effect: Spatial Distributions in the Pupil for Oblique Incidences upon Foveal Cones. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4898.
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Studies of the optical Stiles-Crawford (S-C) effect assume that the relative spatial distribution of light radiated from photoreceptors to the eye’s pupil does not depend on the angle of incidence θ of light upon the myoid. When the entrance pupil is aligned to photoreceptor axes, the incident wave launches the only mode HE11. Light is guided along the photoreceptor, reflected by the inner segment (IS) / outer segment (OS) junction and the OS tip, and guided backwards; therefore the radiation pattern in the pupil follows from to the mode HE11. But for oblique incidences, the modes TE01, TM01 and HE21 can also be excited. Thus the question arises whether light carried by these modes can be reflected and radiated to the eye’s pupil.
The directional characteristics of foveal photoreceptors are determined by measuring the spatial distribution in the eye’s pupil of light radiated from the retina. The distribution of light in the pupil is measured with a CCD camera cooled by liquid nitrogen (Princeton Instruments, Trenton, NJ). The angle of incidence upon photoreceptors is controlled by two stepping motors. We have measured the directional characteristics of foveal photoreceptors as a function of the angle of incidence in a group of 10 normal young subjects at 532 nm.
The directionality factor ρ of photoreceptors inside the sample field (2 deg) had a mean value of 0.221 mm-2 (SD: 0.029 mm-2) when the entrance pupil was aligned to photoreceptor axes. For each of the subjects it decreased as the angle of incidence θ increased. Their mean values were 0.203 mm-2 (SD: 0.032 mm-2) and 0.168 mm-2 (SD: 0.041 mm-2) for θ equal to 2.6 deg and 5.2 deg, respectively.
Light carried forward by the modes TE01, TM01 and HE21 can be reflected, guided backward and radiated to the eye’s pupil. Reflection of these modes is likely to occur at the IS/OS junction. Studies of the optical S-C effect have to take account of the location of the entrance pupil when measuring the directionality factor.
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