PURPOSE. The Tumbling-E and Landolt ring 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 these optotypes. METHOD. Ten normally sighted young adults served as subjects. The Tumbling-E and Landolt rings were tested separately using the method of constant stimuli. The optotypes were presented individually in random size and orientation in the center of a computer monitor. The subjects were initially tested with their best refractive corrections. In the optical blur test conditions, spherical (+1.50 DS) and cylindrical lenses (+1.50 DC x 180, +1.50 DC x 090) were used to simulate simple myopic refractive errors.
RESULTS. Visual acuity thresholds for the Tumbling-E were 0.01 logMAR better for the best correction and spherical blur test conditions and averaged 0.09 logMAR better for the +1.50 DC x 180 lens and 0.02 logMAR better for the +1.50 DC x 090 lens. These differences were significant (F=15.926, p < 0.01). There was a nearly significant trend for the psychometric function to be steeper for the Tumbling-E (F = 4.993, p = 0.052) over all test conditions, with a mean inverse slope of 0.126 compared to 0.164 for the Landolt ring. The slopes of the psychometric functions were unaffected by the optical blur test conditions (F = 2.38, p = 0.092).
CONCLUSIONS. The Tumbling-E and Landolt ring may be best suited for measuring visual acuity for different clinical applications. The Tumbling-E appears to be slightly less sensitive to astigmatic blur. Therefore, the Landolt ring may be the better optotype to use in screenings to detect uncorrected refractive error. However, the generally flatter psychometric functions found with the Landolt rings suggests that less confidence can be placed in the corresponding acuity thresholds. Future work is necessary to determine if the Tumbling-E is a more appropriate optotype for use in situations when the most accurate acuity threshold is required, such as the assessment and treatment of amblyopia.