Wavelength dependence of reflectometric cone photoreceptor directionality

We present evidence for the wavelength dependence of the directionality of light reflected from cone receptor cells (optical StilesCrawford effect): Blue light is more directional than red. According to the waveguide-scattering model of Marcos J. Opt. Soc. Am. A 15 , 2012 (1998), directionality is the sum of a waveguide component and a scattering component. The latter is proportional to 1 over wavelength squared, and it is related to the row-to-row spacing of the cone lattice. Our results allow a firm confirmation of Marcos s theory. For a 1.9-deg foveal area, group mean (n=18) cone spacing was 3.42 m, in good agreement with anatomical data. Group mean waveguide directionality was 0.077 mm