The effects of astigmatism on sensitivity to sinusoidal and square wave gratings

Contrast thresholds for different spatial frequencies were measured for four individuals with optimum optical correction and with 2 D of astigmatism induced at various meridians. Sensitivity for sine waves of low spatial frequencies was unaffected by the astigmatism; however, gross changes were found at high spatial frequencies when the astigmatism was induced with the power meridian perpendicular to the orientation of the stripes. For square waves, the results were comparable at high spatial frequencies, but astigmatism also produced a decrement at 0.2 cycles/degree. This latter effect can be predicted by assuming that astigmatism results in a loss of higher order harmonics in the response to square waves.