Spherical and irregular aberrations are important for the optimal performance of the human eye.

Contrast sensitivity measured psychophysically at different levels of defocus can be used to evaluate the eye optics. Possible parameters of spherical and irregular aberrations, e.g. relative modulation transfer (RMT), myopic shift, and depth of focus, can be determined from these measurements. The present paper compares measured results of RMT, myopic shift, and depth of focus with the theoretical results found in the two eye models described by Jansonius and Kooijman (1998). The RMT data in the present study agree with those found in other studies, e.g. Campbell and Green (1965) and Jansonius and Kooijman (1997). A new theoretical eye model using a spherical aberration intermediate between those of the eye models described by Jansonius and Kooijman (1998) and an irregular aberration with a typical S.D. of 0.3-0.5 D could adequately explain the measured RMT, myopic shift, and depth of focus data. Both spherical and irregular aberrations increased the depth of focus, but decreased the modulation transfer (MT) at high spatial frequencies at optimum focus. These aberrations, therefore, play an important role in the balance between acuity and depth of focus.