Effects of defocus and pupil size on human contrast sensitivity

Defocus lowers the contrast sensitivity function (CSF), producing a complex function with local dips and peaks. Previously, we were able to predict th e shape of the CSF with large pupils from measured transverse aberrations w ith hypermetropic defocus but not with myopic defocus (Atchison et al., 199 8c, J. Opt. Soc. Am. A. 15, 2536). As there is no reason that myopic defocu s should be more difficult to predict than hypermetropic defocus, we modifi ed the procedure to try to improve CSF predictions with myopic defocus. Als o, we extended the study to consider a range of pupil sizes. CSFs were meas ured for three subjects at three defocus levels (in-focus, -2D and +2D) and three pupil sizes (2 mm, 4 mm and 6 mm). Using a diffraction optics model, transverse aberration measures and in-focus CSF measures, we predicted the defocused CSFs. The predicted defocused CSFs were lower than the in-focus CSF as expected, and had complex shapes that varied with defocus and pupil size and between subjects. While a few predictions were poor, generally, th e overall magnitude and shape of the defocused CSFs were well predicted and similarly so for myopic and hypermetropic defocus. Some further improvemen ts in technique are indicated. (C) 1999 The College of Optometrists. Publis hed by Elsevier Science Ltd. All rights reserved.