Overview
EN ISO 7921:2024 (ISO 7921:2024) specifies requirements for near reading charts used to assess and measure near reading acuity. It covers printed, projected and electronic high‑contrast text displays intended for clinical and research use under photopic conditions. The standard defines measurement conventions based on the Latin alphabet and provides a standardized basis for expressing near reading acuity (including logRAD) at a reference viewing distance of 40 cm.
Key topics and requirements
- Scope & applicability: Applies to printed, projected and electronic near reading charts; definitions and requirements apply primarily to the Latin alphabet (with guidance for similar alphabets).
- Measurement basis: Introduces logRAD (logarithm of reading acuity determination) and the reading acuity angle, which are analogous to logMAR but based on lowercase x‑height rather than gap/line width.
- Size notations: Standardizes equivalent notations for near acuity, including decimal reading acuity, M size, N size, reduced Snellen fractions, and logRAD.
- Typeface and layout: Requires use of typefaces similar to Times New Roman (serif) or Helvetica (sans serif), in standard font style (no italics or emphasis), with standard letter spacing.
- Geometry & spacing: Uses a standardized reading distance of 40 cm and specifies x‑height calculations tied to logRAD; line spacing for given text sizes shall not exceed 1.5 line spacing.
- Documentation & conformity: Includes provisions for test methods (type tests and conformity), marking, and accompanying documents; Annex A covers clinical application of near reading acuity notations.
Applications and who uses it
- Clinical practitioners: Optometrists and ophthalmologists use standardized near reading charts for consistent assessment of near vision, low‑vision aids evaluation, and pre/post‑treatment checks.
- Manufacturers: Designers of printed charts, electronic acuity charts, smartphone apps, and ophthalmic instruments rely on the standard to ensure product consistency and regulatory compliance.
- Researchers: Vision scientists and clinical researchers use EN ISO 7921:2024 when comparing chart formats, typefaces, and cross‑linguistic equivalence of reading tests.
- Regulatory and standards bodies: Adopt the standard for national implementation, conformity assessment, and harmonization of near vision testing practices.
Related standards
- ISO 3:1973 - Preferred numbers
- ISO 15004‑1 - Ophthalmic instruments: fundamental requirements and test methods (Part 1)
- IEC 60601‑1 - Medical electrical equipment: general safety and essential performance
EN ISO 7921:2024 ensures reliable, comparable near reading acuity measurement across printed and digital media, supporting clinical accuracy and product interoperability in ophthalmic optics.
