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Benjamin Lochocki, Brian Vohnsen; Single-beam flickering for characterization of the Stiles-Crawford effect across the visible spectrum. Journal of Vision 2013;13(15):P21. doi: 10.1167/13.15.56.
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© ARVO (1962-2015); The Authors (2016-present)
The psychophysical Stiles-Crawford effect (SCE) characterizes a reduction of photopic visibility when light enters the eye towards the edge of the pupil. It is typically characterized in a bipartite or two-beam system which complicates its experimental analysis.
To circumvent this, we present a novel single-beam flickering system for characterization of the SCE across the visible spectrum. Full pupil scans at any angle can be realized while automatically adjusting wavelength, bandwidth and intensity using liquid-crystal tunable color and neutral density filters controlled remotely by the subject. Subjective defocus is corrected at any wavelength by a combination of a current-controlled tunable focus lens in combination with a negative achromatic lens.
Flicker speed is fully adjustable up to 20 Hz (but typically set at 1 Hz or slower) and is synchronized with the liquid crystal variable attenuator allowing real-time luminance control for the traversing test beam with respect to the reference light that enters the eye near the pupil center. The obtained visibility results, for Maxwellianfoveal viewing across 1.5 visual degrees, were fitted to a Gaussian SCE distribution with a characteristic wavelength-dependent directionality parameter. The results confirm the usability of the approach and that reliable directionality measurements can be obtained that are of relevance in the analysis of light-to-cone photoreceptor coupling mechanisms and the role of the SCE for visual function.
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