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

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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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Authors and Affiliations

  1. School of Engineering and Computer Science, Hebrew University, Jerusalem, Israel

    Reuben R. Shamir & Leo Joskowicz

  2. Department of Ophthalmology, Rambam Medical Center, P.O.B 9602, Haifa, 31096, Israel

    Yael G. Friedman, Michael Mimouni & Eytan Z. Blumenthal

Authors
  1. Reuben R. Shamir
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  2. Yael G. Friedman
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  3. Leo Joskowicz
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  4. Michael Mimouni
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  5. Eytan Z. Blumenthal
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Corresponding author

Correspondence to Eytan Z. Blumenthal.

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Conflict of interest

All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; or expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Funding

No funding was received for this research.

Ethical approval

Due to the nature of this simulation, no human participants were involved and no patient data were collected. Therefore, this study was exempt from institutional review board approval and from obtaining informed consent.

Additional information

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.

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Shamir, R.R., Friedman, Y.G., Joskowicz, L. et al. The influence of varying the number of characters per row on the accuracy and reproducibility of the ETDRS visual acuity chart. Graefes Arch Clin Exp Ophthalmol 254, 971–976 (2016). https://doi.org/10.1007/s00417-015-3252-3

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  • DOI: https://doi.org/10.1007/s00417-015-3252-3

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