Contrast sensitivity benefit of adaptive optics correction of ocular aberrations.

While correcting the aberrations of the eye produces large increases in retinal image contrast, the corresponding improvement factors in the contrast sensitivity function have been little explored and results are controversial. We measured the CSF of 4 subjects with and without correcting monochromatic aberrations. Monochromatic CSF measurements were performed at four orientations (0, 45, 90, and 135 deg) and at six spatial frequencies (2-30 c/deg). In two subjects, the CSF was also measured in polychromatic light. The MTF increased on average by 8 times and meridional changes in improvement were associated to individual meridional changes in the natural MTF. CSF increased on average by 1.35 times (only for the mid- and high spatial frequencies) and was lower (0.93 times) for polychromatic light. Under natural aberrations, the horizontal and vertical CSFs tended to be higher than the oblique CSFs, but the meridional differences in the CSF were partially reduced when the aberrations were corrected. The consistently lower benefit in the CSF than in the MTF of correcting aberrations suggests a significant role for the neural transfer function in the limit of contrast perception. Polychromatic aberrations play an additional role in degrading contrast, particularly in the absence of monochromatic high-order aberrations.