The relationship between visual acuity and luminance with contact lenses, compared with the same one obtained with glasses, shows that acuity deteriorates more rapidly with contact lenses than with glasses as luminance is decreased. Spherical aberration of the eye wearing a contact lens is shown to account for the phenomenon, as the anterior surface of the contact lens is spherical in comparison to the aspherical human cornea. With a 3 mm artificial pupil, acuity with contact lenses diminishes with luminance at the same rate as with glasses. At the lowest luminance, the difference in acuity obtained with glasses and with contact lenses is statistically significant. However, the difference is not as large as would be predicted from spherical aberration alone, because of the Stiles-Crawford effect.
Millodot M. Variation of Visual Acuity With Contact LensesA Function of Luminance. Arch Ophthalmol. 1969;82(4):461-465. doi:10.1001/archopht.1969.00990020463007