EN ISO 7921:2024

Ophthalmic optics and instruments - Near reading charts (ISO 7921:2024)

This document applies to printed, projected, and electronic displays of high-contrast text that are designed for assessment and measurement of near reading acuity under photopic conditions.
The definitions and requirements of this document apply to the Latin alphabet.

Augenoptik und ophthalmische Instrumente - Nahlesesehschärfetafeln (ISO 7921:2024)

Dieses Dokument ist anwendbar für gedruckte, projizierte und elektronische Anzeigen von kontrastreichem Text, die für die Beurteilung und Messung der Nahlesesehschärfe unter photopischen Bedingungen (Tageslichtbedingungen) vorgesehen sind.
Die Definitionen und Anforderungen dieses Dokuments sind anwendbar für das Lateinische Alphabet.

Optique et instruments ophtalmiques - Tableaux d’optotypes utilisés pour la mesure de l’acuité de lecture en vision de près (ISO 7921:2024)

Le présent document s’applique aux dispositifs d’affichage de textes à contraste élevé imprimés, projetés et affichés par des moyens électroniques qui sont conçus pour évaluer et mesurer l’acuité de lecture en vision de près dans des conditions photopiques.
Les définitions et les exigences figurant dans le présent document s’appliquent à l’alphabet latin.

Očesna optika in instrumenti - Tablice za preverjanje bližinskega vida (ISO 7921:2024)

Ta mednarodni standard se uporablja za prikaze visokoločljivega besedila, ki so zasnovani za splošno preverjanje bližinskega vida. Ta standard se ne uporablja za merilne sisteme, ki so zasnovani za posebno preskušanje ostrine bližinskega vida, npr. tablice za preverjanje slabega vida oziroma ostrine vida ali tiste, namenjene za sisteme s presvetlitvijo ali elektronsko ustvarjene sisteme.

General Information

• Status: Published
• Publication Date: 20-Feb-2024
• ICS: 11.040.70 - Ophthalmic equipment
• Technical Committee: CEN/TC 170 - Ophthalmic optics
• Drafting Committee: CEN/TC 170 - Ophthalmic optics
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 21-Feb-2024
• Due Date: 30-Jul-2025
• Completion Date: 21-Feb-2024
• Ref Project: SIST EN ISO 7921:2024 - Ophthalmic optics and instruments - Near reading charts (ISO 7921:2024)

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.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2024
Očesna optika in instrumenti - Tablice za preverjanje bližinskega vida (ISO
7921:2024)
Ophthalmic optics and instruments - Near reading charts (ISO 7921:2024)
Augenoptik und ophthalmische Instrumente - Nahsehschärfetafeln (ISO 7921:2024)
Optique et instruments ophtalmiques - Tableaux d’optotypes utilisés pour le mesurage
de l’acuité de lecture en vision de près (ISO 7921:2024)
Ta slovenski standard je istoveten z: EN ISO 7921:2024
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 7921
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2024
EUROPÄISCHE NORM
ICS 11.040.70
English Version
Ophthalmic optics and instruments - Near reading charts
(ISO 7921:2024)
Optique et instruments ophtalmiques - Tableaux Augenoptik und ophthalmische Instrumente -
d'optotypes utilisés pour la mesure de l'acuité de Nahsehschärfetafeln (ISO 7921:2024)
lecture en vision de près (ISO 7921:2024)
This European Standard was approved by CEN on 9 February 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7921:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 7921:2024) has been prepared by Technical Committee ISO/TC 172 "Optics and
photonics" in collaboration with Technical Committee CEN/TC 170 “Ophthalmic optics” the secretariat
of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by August 2024, and conflicting national standards shall
be withdrawn at the latest by August 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 7921:2024 has been approved by CEN as EN ISO 7921:2024 without any modification.

International
Standard
ISO 7921
First edition
Ophthalmic optics and
2024-02
instruments — Near reading charts
Optique et instruments ophtalmiques — Tableaux d’optotypes
utilisés pour la mesure de l’acuité de lecture en vision de près
Reference number
ISO 7921:2024(en) © ISO 2024
ISO 7921:2024(en)
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 7921:2024(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 3
5 Test methods . 5
5.1 Type tests .5
5.2 Conformity .5
6 Accompanying documents . . 5
7 Marking . . 6
Annex A (normative) Clinical application of near reading acuity notations . 7
Bibliography . 8

iii
ISO 7921:2024(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 7,
Ophthalmic optics and instruments.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO 7921:2024(en)
Introduction
This document provides the terms, definitions, and requirements for standardized charts for the assessment
of near reading acuity. Reading is a complex visual task that involves more than the mere identification or
recognition of individual letters, symbols, or other optotypes. The charts used to assess near reading acuity
are intended for the practical purpose of demonstrating whether or not a patient can read sentences or
paragraphs of text of a particular size. This document is not meant to replace or supplant standards for
visual acuity charts for research or for basic clinical assessments, such as visual acuity measurements
before and after cataract surgery.
A patient’s reading ability can be labelled using terms such as “difficult” or “easy”, or “with errors” or
“fluent" or "error-free”. Proper assessment of reading ability requires the use of text that is appropriate for
the patient, for example, based on the patient’s age or educational level. However, the actual determination
of a patient’s near reading acuity based on these and possibly other factors involves clinical evaluation that
is beyond the scope of this document.
This document bases the nominal near reading acuity grade on values given as the logarithm of reading acuity
determination (logRAD). LogRAD is similar to the logarithm of minimum angle of resolution (logMAR), used
in standard visual acuity testing, in that both are based on the angular size of the test target at a particular
viewing distance. However, logRAD specifically depends on the height of lowercase letters, which occur
more frequently than uppercase letters, numbers, and symbols in typical text. On the other hand, logMAR is
determined by the width of an individual line or the size of a gap. For ease of clinical application, equivalent
near reading acuity grades are provided for several common recording notations, including decimal reading
acuity, M size, N size, and reduced Snellen fractions.
This document allows for the use of any typeface that is similar in appearance to either of two common
typefaces: Times New Roman, a typeface with serifs, which is widely used for printed text; and Helvetica,
a sans serif typeface, which is commonly used for both printed charts and electronic displays, such as
computer monitors, laptops, and smartphones.
This document applies to the Latin alphabet. It can also apply to similar alphabets, such as Greek and Cyrillic,
that can be expressed with typefaces similar to Times New Roman or Helvetica. For other writing systems,
such as Arabic, Chinese, Hebrew, Japanese, and Korean, this document can be used as a reference, especially
for researchers who wish to demonstrate equivalence of near reading charts using those writing systems
with charts using the Latin alphabet.

v
International Standard ISO 7921:2024(en)
Ophthalmic optics and instruments — Near reading charts
1 Scope
This document applies to printed, projected, and electronic displays of high-contrast text that are designed
for assessment and measurement of near reading acuity under photopic conditions.
The definitions and requirements of this document apply to the Latin alphabet.
2 Normative references
The following documents are referred to i
...