Validity of Four Current Subjective Tests of Astigmatism

Validity coefficients of astigmatic techniques were obtained from two experiments which consisted of (1) crossed cylinders and parabolic chart with 18 subjects, and (2) regular clock dial, polarized clock dial, and crossed cylinders with 26 subjects. Results showed almost perfect correspondence between crossed cylinders and parabolic chart, and high correlation for adjusted values among the two clock dials and crossed cylinders. The significant difference between the nearly perfect correlation from (1), and high correlation from (2), suggested that either the crossed cylinders or parabolic chart would serve better than the regular or polarized clock dials in the final determination of astigmatism, and that in the confirmation of patients with small degrees of astigmatism, the parabolic chart would perform better than the regular clock dial.