Notch in contrast sensitivity function of optical origin: diffraction effects of acrylic filters

A series of retinal image degrading filters was evaluated by measuring the contrast sensitivity function of four human subjects through the filters (residual CSF). The acrylic filters, with regularly spaced cross-hatches, produced progressively more reduction in the residual CSF as the density of the cross hatching increased. For some of the filters there was a selective loss of a narrow band of spatial frequencies as a result of diffraction effects. This experiment serves to further emphasize the need to rule out optical causes of such notches in the CSF before making a diagnosis of neurological dysfunction.