Wavelength dependence of the Stiles-Crawford effect explained by perception of backscattered light from the choroid.

To explain the wavelength dependence of the directional sensitivity of human foveal cones (Stiles-Crawford I effect) we extended an existing fundus reflectance model for calculation of the total absorption by visual pigment. We took experimental data from literature for both the psychophysical and the optical Stiles-Crawford effect and optimized parameters to fit the experimental data. The wavelength dependence of the Stiles-Crawford effect could be well described with the geometrical optics model. Essential elements are self-screening and the inclusion of backscattered choroidal light for perception.