Background: Given the diversity of visual acuity tests being employed across the world, we compared two frequently applied tests: ETDRS charts and an eight-orientation projected Landolt C test in accordance with ISO 8596 and DIN 58220 part 3. The goals of the investigation were to determine (i) test agreement and (ii) test-retest reliability, to assess (iii) test durations, and (iv) the acceptance of the tests by the examinees as well as the subjects' coping with the tests as rated by the examiner.
Methods: Seventy-five adult subjects with a visual acuity of ≥0.2 (4/20) were included in one of the following groups: normal, media opacity, maculopathy, optic neuropathy, (post)chiasmal lesion, or amblyopia. Visual acuity testing was carried out monocularly, in balanced randomized order and in two runs for each test on the same eye, applying forced choice.
Results: Agreement: Within each group, all tests were performed similarly, within ±0.048 logMAR. Reliability: Across all subject groups, with a probability of 95 %, test-retest differences were <0.18 logMAR for both ETDRS and Landolt tests.
Duration: The Landolt test lasted, on average, 1.8 times longer than ETDRS charts (p < 0.001). Acceptance: Examinees preferred the ETDRS test (p < 0.001), the examiner on average had no preference.
Conclusion: The Landolt C test and the ETDRS test yielded comparable results in visual acuity and test-retest reliability in all disease groups. The ETDRS test was usually faster and more accepted by both examiners and examinees than the Landolt test.