On the resolution of gratings by the astigmatic eye

An investigation on the resolution of gratings by the human eye, commenced by H. H. Emsley in 1925, was continued. The irregular curve representing variation of grating acuity from meridian to meridian was found to be of the same general form in all astigmatic eyes. Experiment showed that the image, produced by an ordinary astigmatic system, of gratings placed in various directions shows irregularities of the same form due to overlapping of the blurred images of the separate lines of the grating. Thus an eye with regular astigmatism will exhibit irregularities in its capacity to resolve gratings at various inclinations, and charts consisting of fine parallel lines are not reliable in testing ocular astigmatism.