Stiles–Crawford effect improves defocused or aberrated retinal image quality

Visual sensitivity is not uniform across the pupil. Sensitivity peaks near the pupil center and is reduced at the pupil margins (Stiles–Crawford effect or SCE). Is there any functional advantage derived from this property? The SCE can be considered equivalent to apodization of the pupil, but no functional value of this apodization has been observed for well-focused images.1-3 However, the most significant effect of SCE may be to increase depth of focus.4,5 Using a wave-optics model of the human eye, we incorporate apodization by changing the pupil transmission function from a uniform function into an SCE function. We calculate the influence of SCE on the OTF with defocus error or ocular spherical aberration. Our results show that (1) Stiles–Crawford apodization significantly improves contrast for defocused images for large pupils, and (2) The Stiles-Crawford apodization is also effective at improving image quality when the eye exhibits significant spherical aberration.