[Comparison of visual acuity measured using Landolt-C and ETDRS charts in healthy subjects and patients with various eye diseases].

PURPOSE

Results of visual acuity determination can differ depending on the stimuli being used, even if their critical details appear under the same visual angle. In this study, visual acuity measured with the Landolt C was compared to acuity measured with ETDRS charts in subjects with and without visual disorders.

PATIENTS AND METHODS

One hundred patients (age 8 to 90 years) with strabismus amblyopia (39), refractive amblyopia (5), cataract (24) and maculopathy (32) as well as 13 healthy volunteers (age 18 to 33 years) were examined. Retro-illuminated ETDRS 1, 2 and R charts (Lighthouse) and a retro-illuminated Landolt C chart with the same arrangement of optotypes (Precision Vision) were used. Three out of 5 optotypes in each line had to be correctly identified. In the patient group, the eyes with the lower visual acuity were tested, while the right eyes of the healthy subjects were monitored. Wrong answers were monitored and the results were noted in interpolated logMAR.

RESULTS

Differences between Landolt C (LC) and ETDRS acuity were only small and statistically not significant. LogMAR values (SEM in parentheses) 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), refractive amblyopia: 0.27 (0.04)/ 0.23 (0.05), cataract: 0.57 (0.07)/ 0.51 (0.07), retinal disease: 0.67 (0.06)/ 0.61 (0.06), 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 in strabismus amblyopia in favour of ETDRS 1 values. ETDRS 2 and R charts yielded similar results.

CONCLUSIONS

In healthy subjects and in patients with various eye disorders including strabismus amblyopia, there was only a slight difference between visual acuity measured by ETDRS charts compared to the Landolt C. Comparing data of different settings it must be considered that in the lower visual acuity range (< 0.32), the mean ETDRS acuity of adults overestimates the Landolt C acuity by 0.5 and 1.0 line.