The effects of optical defocus on the legibility of the Tumbling-E and Landolt-C

Optom Vis Sci. 2002 Jun;79(6):389-93. doi: 10.1097/00006324-200206000-00013.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Astigmatism / physiopathology
  • Humans
  • Myopia / physiopathology
  • Reading
  • Sensory Thresholds
  • Vision Tests / methods*
  • Visual Acuity*