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07.01.2016 | Miscellaneous | Ausgabe 5/2016

Graefe's Archive for Clinical and Experimental Ophthalmology 5/2016

The influence of varying the number of characters per row on the accuracy and reproducibility of the ETDRS visual acuity chart

Zeitschrift:
Graefe's Archive for Clinical and Experimental Ophthalmology > Ausgabe 5/2016
Autoren:
Reuben R. Shamir, Yael G. Friedman, Leo Joskowicz, Michael Mimouni, Eytan Z. Blumenthal
Wichtige Hinweise
The authors have full control of all primary data and agree to allow Graefe’s Archive for Clinical and Experimental Ophthalmology to review the data upon request.

Abstract

Background

As part of an effort to improve upon the Snellen chart, we provide a standardized version of the ETDRS chart utilizing five characters in each row. The choice of five characters contradicts the recommended ten characters per row determined by the NAS-NRC, a committee established to provide guidelines for testing visual acuity. We set out to quantify the influence of varying the number of characters per line on the ETDRS chart with respect to the accuracy and reproducibility of visual acuity measurement.

Methods

Eleven different ETDRS charts were created, each with a different number of characters appearing in each row. A computer simulation was programmed to run 10,000 virtual patients, each with a unique visual acuity, false-positive and false-negative error value.

Results

Accuracy and reproducibility were found to roughly correlate with the number of characters present in each row, such that charts with 1, 3, 5, 7, 9, and 11 characters per row provided accuracy of 0.164, 0.094, 0.078, 0.073, 0.071, and 0.070 logMAR, respectively. A non-linear relationship was observed, with little improvement found beyond seven characters per row. In addition, charts with an even number of characters per row provided higher accuracy than their greater-number odd counterparts. In certain instances, accuracy and reproducibility were not well correlated.

Conclusions

Increasing the number of characters per row in the ETDRS chart provides a trade-off between accuracy and test duration. An optimized chart layout would take these findings into account, allowing for the use of different chart layouts for clinical versus research settings.

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