How Accurate are Our Near Reading Charts? An Assessment of 19 Charts Against ISO Standards

Measuring near vision provides clinicians with valuable insight into visual function. There is limited information on the accuracy of available reading charts used frequently in community practice. This study aimed to measure internationally available reading charts to determine how they compare to international standards.

Commercial and device manufacturer-provided reading charts available in community optometry clinics were scanned at 600 dots per inch. A Gaussian adaptive threshold was used to facilitate repeatable measurements. X-heights of letters were measured independently by three researchers. Contrast levels and line spacing were also estimated. Results for each chart were compared with ISO Standards. Intraclass correlation coefficient was used to assess intergrader agreement.

Of the 19 reading charts that were measured, only one chart (5.26%) had text sizes that were all within tolerance. There was high variability in size observed between charts. Twelve charts (63.2%) used serif fonts and seven used sans-serif (36.8%). Text on serif charts tended to be smaller than required (µ = -9.63%) compared to sans-serif (µ = +4.96%). All charts met the line spacing requirements and the minimum required contrast level; however, some charts were printed on laminated or satin plastic, which does not meet the standard of using a matte surface. There was high interrater agreement (ICC(2,1) = 1.00), indicating a highly repeatable measurement technique.

This study found that the tested reading charts displayed significant variability in text size. Although some charts had more lines of text within size tolerances than others, none met all the requirements of the International Standard. Clinicians and researchers should take care when interpreting changes in near reading acuity when multiple charts have been used, especially as part of shared care models or when monitoring progressive vision changes. A free UC/UWA Reading Chart has been developed as a result of this study, which conforms to the ISO Standard.