Abstract
The Stiles-Crawford effect of the first kind (SCE-I) describes a psychophysical change in perceived brightness related to the angle of incidence of a ray of light onto the retina. The effect is commonly explained as being due to angular-dependent waveguiding by foveal cones, yet the SCE-I is largely absent from similar-shaped rods suggesting that a different mechanism than waveguiding is at play. To examine this, we have devised a flickering pupil method that directly measures the integrated SCE-I for normal pupil sizes in normal vision rather than relying on mathematical integration of the standard SCE-I function as determined with Maxwellian light. Our results show that the measured effective visibility for normal foveal vision is related to visual pigment density in the three-dimensional retina rather than waveguiding. We confirm the experimental findings with a numerical absorption model using Beer-Lambert’s law for the visual pigments.