[Reproducibility of visual acuity measurement using the ETDRS chart in daily clinical practice]

To evaluate reproducibility of visual acuity measurements using the ETDRS chart at successive monthly visits in patients with stable macular pathology.

Visual acuity was measured using the ETDRS chart at 6 consecutive monthly examinations. Relative standard deviation of visual acuity was measured for every patient. Analysis of the results by type of pathology, age, sex and examiner experience was performed.

One hundred and three patients were included. Mean patient age was 72.7±12.4 years. A total of 68.9% of the patients suffered from AMD. Mean visual acuity was 47.4±9.5 ETDRS letters. Mean reproducibility of the measurement estimated by relative standard deviation over the 618 examinations was 5.4±2.8% (CI95%: 4.9-6%) with extremes values of 0.4 and 7.8 letters. Relative standard deviation corresponding to the mean ETDRS score (47.4 letters) was 2.5 letters. Reproducibility of visual acuity measurement was better in patients under 76 years, pseudophakes, or with a visual acuity better than 50 letters (P<0.05). Variability of the measurement increased with age (r²=13%, P=0.001) and with low visual acuity (r²=35%, P<0.0001) and was larger in patients suffering from AMD than those suffering from other conditions. Examiner experience did not seem to influence reproducibility of the measurement.