How accurate are our near reading charts? An assessment of 19 charts against ISO 7921:2024 standards.

Introduction:
Near vision assessment provides clinicians with important information about visual function, yet limited data exist on the accuracy of reading charts commonly used in community practice.
Aims:
To measure near reading charts to determine how they compare to an international standard (ISO 7921:2024), and to develop a chart conforming to this standard.
Methods:
Commercially and device manufacturer-provided reading charts were scanned at 600 dots per inch, and Gaussian adaptive thresholding applied to facilitate repeatable measurements. Letter x-heights were measured in pixels by three researchers and converted to millimetres. Contrast levels and line spacing were also measured. Results were compared with ISO Standards, with intraclass correlation coefficient used to assess intergrader agreement.
Results:
High variability was observed between charts. Only one of the 19 tested charts (5%) had all text sizes within tolerance. Serif charts tended to have smaller text than required (µ=−9.65%) while sans-serif tended to be larger (µ=+4.96%). All charts met line spacing and minimum contrast level requirements, though some failed to comply with the matte surface requirement. Interrater agreement was high (ICC(2,1)=1.00), indicating a highly repeatable measurement technique. A new chart, the UC/UWA Reading Chart, was developed which meets all ISO 7921:2024 criteria.
Conclusions:
Significant variability in text size was identified across reading charts, and none met all ISO 7921:2024 requirements. Clinicians and researchers should exercise caution when interpreting changes in near reading acuity when different charts are used, particularly in shared-care settings or when monitoring progressive conditions.
Impact:
Accurate near reading acuity measurement is essential for detecting true clinical changes to vision.