(2) In most eyes this retinal directional sensitivity, (which became known as the Stiles-Crawford Effect) is approximately symmetrical with respect to the centre of the pupil, although variations with refractive error have been shown, particularly in myopia where the cone receptors frequently point towards the nasal edge of the pupil.
When retinal receptors are misaligned as in retinal amblyopia, or in cases of central serous retinopathy, the Stiles-Crawford Effect will be slightly abnormal.
The Stiles-Crawford Effect plays an important role in the effect of pupil size on chromostereopsis.
A Dutch study by Vos (10) first suggested the role of the Stiles-Crawford Effect in colour stereopsis, suggesting that the shifts in chromostereopsis with pupil size are due to decentration of the peak of the Stiles-Crawford Effect with respect to the pupil, as confirmed by Ye et al.
The Stiles-Crawford Effect may well be of greatest importance to the visual process by suppressing the effect of stray light within the ocular media.
Psychophysical studies have failed to show a significant Stiles-Crawford Effect for rod photoreceptors.
Although measurements of the Stiles-Crawford Effect are not easy to make outside of a laboratory setting, measurements were made on a limited number of anomalous trichromats by Walraven and Leebeck.
Thirdly, as a consequence of the Stiles-Crawford effect
, whereby peripherally incident rays of light are less visually effective on cone receptors compared to centrally incident light, peripheral light rays that are refracted more due to spherical aberration will be perceived less.