ABSTRACT: Background. The Tumbling‐E and Landolt‐C are both used to test visual acuity in young, illiterate, or non–English‐speaking patients. In this study, we sought to determine how optical blur affects visual acuity thresholds measured with both of these optotypes. Methods. Ten subjects were tested with 4‐position Tumbling‐E and Landolt‐Cs using the method of constant stimuli. The subjects were tested wearing their habitual corrections and with +1.50 D spherical and cylindrical lenses to simulate myopic refractive errors in the optical blur test conditions. Results. Visual acuity thresholds for the Tumbling‐E were slightly better for all test conditions, while the largest threshold difference between the test letters was found for the simulated against‐the‐rule astigmatism. For both test letters, vertical orientations were more difficult to resolve than horizontal. Also, the slopes of the psychometric functions were steeper for the Tumbling‐E than for the Landolt‐C. Conclusions. The Tumbling‐E can be considered comparable with the Landolt‐C except for the simulated against‐the‐rule‐astigmatism test condition. Although the ranges are quite large, the average psychometric functions of the Landolt‐Cs are flatter, which gives rise to the possibility that more confidence can be placed in the visual acuity thresholds obtained with the Tumbling‐E.
Reich et al. (Sat,) studied this question.