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Updated: Sep 30, 2026
Measuring the Behavioral Effects of Intraocular Scatter
Published on: February 18, 2021
The effects of optical defocus on the legibility of the Tumbling-E and Landolt-C
Lewis N Reich1, Michele Ekabutr
1NOVA Southeastern University, College of Optometry, Fort Lauderdale, Florida 33328-2018, USA. lreich@hpd.acast.nova.edu
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.
