title: The influence of varying the number of characters per row on the accuracy and reproducibility of the ETDRS visual acuity chart.
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.
authors.affiliation: School of Engineering and Computer Science, Hebrew University, Jerusalem, Israel.
authors.forename: Reuben R
authors.initials: RR
authors.lastname: Shamir
authors.affiliation: Department of Ophthalmology, Rambam Medical Center, P.O.B 9602, Haifa, 31096, Israel.
authors.forename: Yael G
authors.initials: YG
authors.lastname: Friedman
authors.affiliation: School of Engineering and Computer Science, Hebrew University, Jerusalem, Israel.
authors.forename: Leo
authors.initials: L
authors.lastname: Joskowicz
authors.affiliation: Department of Ophthalmology, Rambam Medical Center, P.O.B 9602, Haifa, 31096, Israel.
authors.forename: Michael
authors.initials: M
authors.lastname: Mimouni
authors.affiliation: Department of Ophthalmology, Rambam Medical Center, P.O.B 9602, Haifa, 31096, Israel. e_blumenthal@rambam.health.gov.il.
authors.forename: Eytan Z
authors.initials: EZ
authors.lastname: Blumenthal
mesh_terms: D003198:Computer Simulation; D005189:False Positive Reactions; D006801:Humans; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D014787:Vision Tests / Q000295:instrumentation* / Q000592:standards*; D014792:Visual Acuity / Q000502:physiology*
keywords: Accuracy; Characters; ETDRS; Number; Reproducibility; Row; Visual acuity