The effect of optical degradation on the contrast sensitivity function measured at the fovea and in the periphery

Contrast sensitivity functions (CSF's) were measured for a zone of 0.5 degree angular radius at the fovea and for annular zones extending from 0.5 degrees eccentricity to 1 degree, from 1 to 2 degrees and from 2 to 4 degrees. The effect of optical degradation was taken into account by the application of a correction factor determined from the Modulation Transfer Function (MTF). Using the reciprocal of the peak of the CSF [1/SF (max)] as a parameter, the effect of applying the MTF correction on the CSF with eccentricity was determined. The effect of applying an MTF correction is significantly to increase the rate of change of 1/SF (max) with eccentricity. Since it has been reported that hyperacuity is relatively unaffected by optical degradation, it is proposed that the differing effects of optical degradation between grating acuity and hyperacuity may account, at least partially, for the different rates of decline of these thresholds with eccentricity. The implications of this proposal for M-scaling theories and strategies are considered.