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R. C. Becker, G. Teichler, M. Graf; Comparison of Landolt-C and ETDRS- Visual Acuity in Healthy Subjects and Patients With Different Eye Diseases. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4887.
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Assesment of visual acuity depends on the optotypes used for measurement. The ability to recognize different optotypes differs even if their critical detail appears under the same visual angle. Since optotypes are evaluated on individuals with good visual acuity and without eye disorders, differences in the lower visual acuity range cannot be excluded. This especially applies for patients with strabismus amblyopia. In this study, visual acuity as measured with the commonly used ETDRS charts was compared to the Landolt C acuity in healthy subjects and patients with different eye disorders.
100 patients (age 8-90 years, median 60.5) with different eye disorders (39 strabismus amblyopia, 24 cataract, 32 retinal disease, 5 refractive amblyopia) and 13 healthy volunteers (age 18-33 years, median 24) were tested. Visual acuity assessment was performed using retroilluminated ETDRS 1 charts and ETDRS-type Landolt C charts (Precision Vision). 3 out of 5 optotypes per line had to be correctly identified, while wrong answers were monitored. In the group of patients, the eyes with the lower visual acuity, and for the healthy subjects, the right eyes were evaluated. All units of acuity are given in logMAR notation.
Differences between Landolt C (LC) and ETDRS 1 acuity were small and statistically not significant. The mean logMAR values (SEM) for LC / ETDRS 1 were: entire group: 0.60 (0.04) / 0.55 (0.04), strabismus amblyopia: 0.85 (0.08) / 0.80 (0.08), cataract: 0.57 (0.07) / 0.51 (0.07), retinal disease: 0.67 (0.06) / 0.61 (0.06), refractive amblyopia: 0.27 (0.04) / 0.23 (0.05), healthy eyes: -0.17 (0.03) / -0.17 (0.02). The mean difference between LC and ETDRS 1 was 0.49 lines in the entire group and 0.51 lines for the eyes with strabismus amblyopia, with higher values for ETDRS 1. In the acuity range below 0.1, the mean difference between LR and ETDRS 1 was 0.42 lines for the entire group and 0.33 lines for the eyes with strabismic amblyopia with slightly higher values for ETDRS 1 in both groups. This also applies for the entire and the lower visual acuity range for the patients with cataract, retinal disease, refractive amblyopia and the healthy eyes.
Using ETDRS- and ETDRS-type Landolt C charts, there was only a slight overestimation of visual acuity using ETDRS charts, even in patients with different eye disorders. This also applies for the lower visual acuity area. However, small differences have to be considered.
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