Enhancing the Efficiency of Cross-Cylinder Astigmatism Testing

Abstract

The crossed cylinder was introduced by Stokes in 1849 and popularized three quarters of a century later by EDWARD JACKSON [1]. The crossed cylinder is most often used to refine axis and power of a presumptive cylinder determined by some method such as retinoscopy, and the testing involves the use of forced choice. Sensitivity is enhanced when differences in blur for paired stimuli are maximized for a given amount of error. Fogging is avoided since small amounts of accommodation are inconsequential and because the presence of any baseline blur diminishes contrast between paired presentations. Intentional overcorrection of the presumptive cylinder should be avoided [2,3].