BS EN ISO 7921-2024 PDF

Full title and description

STB BS EN ISO 7921-2024 — Ophthalmic optics and instruments — Near reading charts. This designation represents the ISO international standard ISO 7921:2024 and its EN/BS national adoptions for standardized printed, projected and electronic near‑reading charts used to assess near reading acuity.

Abstract

Specifies definitions, design requirements and test methods for high‑contrast near‑reading charts intended to measure near reading acuity under photopic (well‑lit) conditions. The standard defines a clinical notation based on logRAD (logarithm of reading‑acuity determination) and relates x‑height, M/N sizes and other common notations; requirements apply to the Latin alphabet and to printed, projected and electronic displays.

General information

• Status: Published / Valid (international ISO publication and adopted as BS EN national edition).
• Publication date: ISO publication: 9 February 2024 (ISO 7921:2024); BS EN adoption/publication: 22 February 2024 (BS EN ISO 7921:2024). (National adoptions may carry slightly different publication dates and pagination.)
• Publisher: ISO (originating international publisher); adopted/published nationally by bodies such as BSI when issued as BS EN ISO 7921:2024.
• ICS / categories: 11.040.70 — Ophthalmic equipment / Ophthalmic optics and instruments.
• Edition / version: Edition 1 (2024) — ISO 7921:2024, adopted as EN/BS national editions in 2024.
• Number of pages: ISO technical text: 8 pages (ISO PDF); national EN/BS adoptions typically show expanded pagination in their published national documents (examples: BS EN version listed as 18 pages).

Scope

This document applies to printed, projected and electronic displays of high‑contrast text designed for assessment and measurement of near reading acuity at standard near viewing conditions (photopic illumination). It defines terms (for example logRAD, reading acuity angle, x‑height, M and N sizes), chart design and layout principles, tolerances, test/verification methods and required information for manufacturers and users; the normative requirements address the Latin alphabet.

Key topics and requirements

• Definitions and notation: introduction of logRAD as the principal clinical notation for near reading acuity and equivalence tables linking logRAD to decimal, M size, N size and reduced Snellen.
• Chart formats: rules for printed, projected and electronic chart formats (continuous high‑contrast text passages rather than isolated optotypes).
• Typeface and layout guidance: allowance for typefaces similar to common serif/sans‑serif faces, limits on styling (no italics, controlled spacing), recommended line spacing and geometric progression of sizes (logarithmic progression).
• Size metrics and tolerances: x‑height as the reference measure, required geometric size progression, and permissible manufacturing tolerances on x‑height and related measures.
• Illumination, luminance and contrast: requirements or recommendations for background luminance ranges and minimum text/background contrast for reliable testing (guidance for printed and electronic displays).
• Electronic display considerations: pixel‑pitch and resolution guidance to ensure equivalence with printed charts and avoid aliasing or rendering artifacts that could affect acuity measurement.
• Test and verification methods: type tests and conformity checks for chart dimensions, luminance/contrast and marking; manufacturer documentation and marking requirements.

Typical use and users

Primary users are ophthalmic instrument and chart manufacturers, eye‑care clinicians and orthoptists, medical device software developers (visual‑acuity/reading apps and electronic displays), clinical researchers studying reading performance, and regulatory/conformity assessment bodies evaluating chart performance and labeling. The standard is used to design charts, validate electronic implementations and to standardize near reading acuity reporting in clinical settings.

Related standards

Standards referenced or commonly used alongside ISO 7921:2024 include ISO 3:1973 (preferred numbers / geometric progressions), ISO 15004‑1 (ophthalmic instruments — general requirements) and IEC 60601‑1 (medical electrical equipment — safety). Other ophthalmic visual‑acuity documents (distance acuity standards and local national adoptions) are often consulted for comprehensive test protocols.

Keywords

near reading charts; near reading acuity; logRAD; x‑height; M size; N size; ophthalmic optics; chart design; luminance; contrast; electronic displays; photopic conditions.

FAQ

Q: What is this standard?

A: ISO 7921:2024 (adopted as BS EN ISO 7921:2024 and national editions) is the international standard that defines requirements and test methods for near‑reading charts used to assess near reading acuity under photopic conditions.

Q: What does it cover?

A: It covers definitions (logRAD, reading acuity angle, x‑height, M/N sizes), chart design and layout rules for printed/projected/electronic charts, sizing progressions and tolerances, luminance/contrast guidance, electronic display requirements, and type/test methods and manufacturer documentation.

Q: Who typically uses it?

A: Chart and device manufacturers, clinicians and orthoptists, software developers for visual‑acuity applications, clinical researchers and conformity/regulatory assessors.

Q: Is it current or superseded?

A: ISO 7921:2024 is the current edition (first edition 2024). National EN/BS adoptions issued in 2024 adopt the ISO text; check your national standards body for exact national publication and confirmation of status.

Q: Is it part of a series?

A: ISO 7921:2024 addresses near reading charts specifically; it relates to other ophthalmic standards (general instrument requirements and other visual‑acuity standards) but is a standalone document for near‑reading acuity.

Q: What are the key keywords?

A: near reading charts, near reading acuity, logRAD, x‑height, M size, N size, luminance, contrast, electronic display, ophthalmic optics.