EN ISO 15253:2021

Ophthalmic optics and instruments - Optical and electro-optical devices for enhancing low vision (ISO 15253:2021)

This document is applicable to optical and electro-optical devices specified by the manufacturer for use by visually impaired persons as low vision aids. This document specifies requirements and test methods for optical and electro-optical devices specified by the manufacturer for use by visually impaired persons as low vision devices.
Implantable low vision devices are excluded.

Augenoptik und ophthalmische Instrumente - Optische und elektrooptische vergrößernde Sehhilfen für Sehbehinderte (ISO 15253:2021)

Dieses Dokument ist anwendbar für optische und elektrooptische Geräte, die vom Hersteller für die Ver¬wendung durch sehbehinderte Personen als Sehhilfen vorgesehen sind. Dieses Dokument legt Anforderungen und Prüfverfahren für optische und elektrooptische Geräte fest, die vom Hersteller für die Verwendung durch sehbehinderte Personen als Sehhilfen vorgesehen sind.
Implantierbare Sehhilfen sind ausgenommen.

Optique et instruments ophtalmiques - Dispositifs optiques et électro-optiques pour malvoyants (ISO 15253:2021)

Le présent document est applicable aux dispositifs optiques et électro-optiques destinés, selon les indications du fabricant, à être utilisés par des personnes malvoyantes comme systèmes d'aide à la vision. Le présent document spécifie les exigences et les méthodes d'essai applicables aux dispositifs optiques et électro-optiques conçus par le fabricant pour servir d'aides à la vision chez les personnes malvoyantes.
Il ne concerne pas les implants oculaires.

Očesna optika in instrumenti - Optične in elektrooptične naprave za izboljšanje slabovidnosti (ISO 15253:2021)

General Information

• Status: Published
• Publication Date: 13-Jul-2021
• Withdrawal Date: 30-Jan-2022
• 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: 14-Jul-2021
• Completion Date: 14-Jul-2021
• Ref Project: SIST EN ISO 15253:2021 - Ophthalmic optics and instruments - Optical and electro-optical devices for enhancing low vision (ISO 15253:2021)

Relations

• Replaces: EN ISO 15254:2009 - Ophthalmic optics and instruments - Electro-optical devices for enhancing low vision (ISO 15254:2009)
• Effective Date: 21-Jul-2021
• Replaces: EN ISO 15253:2000/AC:2001 - Ophthalmic optics and instruments - Optical devices for enhancing low vision (ISO 15253:2000)
• Effective Date: 21-Jul-2021
• Replaces: EN ISO 15253:2000 - Ophthalmic optics and instruments - Optical devices for enhancing low vision (ISO 15253:2000)
• Effective Date: 04-Dec-2019

Overview

EN ISO 15253:2021 - "Ophthalmic optics and instruments - Optical and electro‑optical devices for enhancing low vision" - is the 2021 CEN-adopted version of ISO 15253. It sets out requirements and test methods for optical and electro‑optical low vision devices specified by the manufacturer for use by visually impaired persons. Implantable low vision devices are explicitly excluded. The standard merges and updates earlier ISO documents to provide a single, harmonized reference for designers, manufacturers, test laboratories and regulators.

Key topics and technical requirements

The standard covers classification, performance requirements and standardized test methods for low vision aids, including:

• Classification

  • Optical devices: distance, near/intermediate, or devices intended to alter retinal illumination/contrast.
  • Electro‑optical devices: electronic magnifiers and similar systems.

• General requirements

  • Risk assessment and risk management
  • Materials, dimensions and weight
  • Flammability/ignitability, resistance to perspiration
  • Robustness and drop resistance

• Optical device requirements

  • Spatial resolution
  • Equivalent power (for near/intermediate magnifiers)
  • Magnification and lateral variation of magnification
  • Exit image distance (stand magnifiers)
  • Entrance pupil diameter (telescopes)
  • Transmittance and image relocation
  • Filters and tints for light sensitivity or contrast enhancement

• Electro‑optical device requirements

  • Display size and magnification characteristics
  • Ambient temperature operating range
  • Image characteristics and uniformity of magnification
  • Object (X–Y) table and working distance
  • Text‑to‑speech functionality and electrical safety

• Test methods

  • Spatial resolution tests, magnification (angular/transverse), exit image distance, display magnification and uniformity, plus procedures for lateral variation of magnification.

• Manufacturer information

  • Marking, instructions for use and performance information required for end users and clinicians.

Applications and who uses this standard

EN ISO 15253:2021 is intended for practical use by:

• Manufacturers and product designers of low vision aids to specify design, safety and performance.
• Testing laboratories to verify conformance using harmonized test methods.
• Clinicians, low vision specialists and occupational therapists seeking standardized performance data for device selection and fitting.
• Procurement and regulatory bodies evaluating compliance and safety for market access.
• Assistive technology developers integrating optical/electronic components (e.g., magnifiers with text‑to‑speech).

Practical use cases include product development, conformity assessment, clinical device selection and comparative product specifications for procurement.

Related standards

• This edition supersedes earlier EN ISO 15253:2000 and EN ISO 15254:2009; it merges ISO 15253 and ISO 15254 requirements.
• It is published under the ISO/CEN Vienna Agreement and adopted by CEN as EN ISO 15253:2021.

Keywords: EN ISO 15253:2021, low vision devices, optical and electro‑optical devices, ophthalmic optics, low vision aids, test methods, magnification, spatial resolution, text-to-speech.

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2021
Nadomešča:
SIST EN ISO 15253:2001
SIST EN ISO 15253:2001/AC:2001
SIST EN ISO 15254:2009
Očesna optika in instrumenti - Optične in elektrooptične naprave za izboljšanje
slabovidnosti (ISO 15253:2021)
Ophthalmic optics and instruments - Optical and electro-optical devices for enhancing
low vision (ISO 15253:2021)
Augenoptik und ophthalmische Instrumente - Optische und elektrooptische vergrößernde
Sehhilfen für Sehbehinderte (ISO 15253:2021)
Optique et instruments ophtalmiques - Dispositifs optiques et électro-optiques pour
malvoyants (ISO 15253:2021)
Ta slovenski standard je istoveten z: EN ISO 15253:2021
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 15253
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2021
EUROPÄISCHE NORM
ICS 11.040.70 Supersedes EN ISO 15253:2000, EN ISO
15253:2000/AC:2001, EN ISO 15254:2009
English Version
Ophthalmic optics and instruments - Optical and electro-
optical devices for enhancing low vision (ISO 15253:2021)
Optique et instruments ophtalmiques - Dispositifs Augenoptik und ophthalmische Instrumente - Optische
optiques et électro-optiques pour malvoyants (ISO und elektrooptische vergrößernde Sehhilfen für
15253:2021) Sehbehinderte (ISO 15253:2021)
This European Standard was approved by CEN on 28 June 2021.

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, Turkey 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
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15253:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 15253:2021) 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 January 2022, and conflicting national standards shall
be withdrawn at the latest by January 2022.
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.
This document supersedes EN ISO 15253:2000, EN ISO 15253:2000/AC:2001 and EN ISO 15254:2009.
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 websites.
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, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 15253:2021 has been approved by CEN as EN ISO 15253:2021 without any modification.

INTERNATIONAL ISO
STANDARD 15253
Second edition
2021-06
Ophthalmic optics and instruments —
Optical and electro-optical devices for
enhancing low vision
Optique et instruments ophtalmiques — Dispositifs optiques et
électro-optiques pour malvoyants
Reference number
ISO 15253:2021(E)
©
ISO 2021
ISO 15253:2021(E)
© ISO 2021
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 2021 – All rights reserved

ISO 15253:2021(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification . 9
4.1 Optical devices . 9
4.1.1 Distance vision . . 9
4.1.2 Near and intermediate vision . 9
4.1.3 Retinal illumination reduction or contrast enhancement . 9
4.2 Electro-optical devices . 9
5 Requirements . 9
5.1 General . 9
5.1.1 Risk assessment and management . 9
5.1.2 Materials . 9
5.1.3 Dimensions and weight . 9
5.1.4 Flammability/Ignitability.10
5.1.5 Resistance to perspiration .10
5.1.6 Robustness .10
5.1.7 Resistance to drop .10
5.2 Optical devices .10
5.2.1 Spatial resolution .10
5.2.2 Equivalent power (applies to optical devices designed for near or
intermediate use) .10
5.2.3 Magnification .11
5.2.4 Exit image distance (applies to stand magnifiers) .11
5.2.5 Entrance pupil diameter (applies to telescopes) .12
5.2.6 Transmittance .12
5.2.7 Image relocation .12
5.3 Electro-optical devices .12
5.3.1 Display size .12
5.3.2 Ambient temperatures . . .12
5.3.3 Image characteristics .12
5.3.4 Object (XY) table .13
5.3.5 Electro-optical device working distance .13
5.3.6 Text to speech system .13
5.3.7 Electrical requirements .13
6 Test methods .13
6.1 General .13
6.2 Optical devices .14
6.2.1 Spatial resolution test .14
6.2.2 Equivalent power – Magnifiers .18
6.2.3 Angular magnification – Telescopes .18
6.2.4 Transverse magnification – Stand magnifiers .18
6.2.5 Lateral variation of magnification test .18
6.2.6 Exit image distance – Stand magnifiers .18
6.3 Electro-optical devices .18
6.3.1 Display magnification test .18
6.3.2 Uniformity of magnification .18
7 Information to be provided by the manufacturer .18
7.1 Marking .18
7.2 Instructions for use .20
ISO 15253:2021(E)
Annex A (informative) Determination of lateral variation of magnification .21
Bibliography .26
iv © ISO 2021 – All rights reserved

ISO 15253:2021(E)
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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 7, Ophthalmic optics, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 170, Ophthalmic optics, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition of ISO 15253:2000 and the second edition of
ISO 15254:2009, which have been technically revised.
The main changes compared to the previous edition are as follows:
— merger of ISO 15253 and ISO 15254;
— revision of normative references;
— revision and re-organisation of terms and definitions;
— addition of new requirements for filters and tints, image relocation, and text to speech;
— editorial revision of the document.
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.
ISO 15253:2021(E)
Introduction
This document represents the merger of two earlier related standards for low vision devices – one for
optical devices only (first edition of ISO 15253) and another for electro-optical devices (ISO 15254) –
and updating of terms, definitions, and requirements. It also includes new requirements for
— filters and tints, such as for users with extreme light sensitivity or reduced contrast sensitivity,
independent of visual acuity or visual field loss,
— image relocation, such as with prisms or mirrors for users with visual field loss or eye- or head-
movement restriction, and
— text to speech for electro-optical devices that offer such capability.
The reader is reminded that the requirements within this document apply to the manufacturer of low
vision devices. While the requirements can also pertain to how a particular device will function for the
low vision user, some factors and variables about the user may not be known to the manufacturer and
thus specific requirements cannot be made. For example, the system resolution of an electro-optical
device is governed by pixel size and density for both the camera and display, while the spatial resolution
for the user depends on the size of the display and the distance at which the user views the display.
vi © ISO 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 15253:2021(E)
Ophthalmic optics and instruments — Optical and electro-
optical devices for enhancing low vision
1 Scope
This document is applicable to optical and electro-optical devices specified by the manufacturer for
use by visually impaired persons as low vision aids. This document specifies requirements and test
methods for optical and electro-optical devices specified by the manufacturer for use by visually
impaired persons as low vision devices.
Implantable low vision devices are excluded.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 12312-1, Eye and face protection — Sunglasses and related eyewear — Part 1: Sunglasses for general
use
ISO 12870, Ophthalmic optics — Spectacle frames — Requirements and test methods
ISO 14889, Ophthalmic optics — Spectacle lenses — Fundamental requirements for uncut finished lenses
ISO 14971, Medical devices — Application of risk management to medical devices
ISO 15004-1, Ophthalmic instruments — Fundamental requirements and test methods — Part 1: General
requirements applicable to all ophthalmic instruments
ISO 15004-2, Ophthalmic instruments — Fundamental requirements and test methods — Part 2: Light
hazard protection
IEC 60601-1, Medical electrical equipment — Part 1: General requirements for basic safety and essential
performance
IEC 60601-1-2, Medical electrical equipment — Part 1-2: General requirements for basic safety and essential
performance — Collateral standard: Electromagnetic disturbances — Requirements and tests
IEC 60601-1-3, Medical Electrical Equipment — Part 1-3: General Requirements for Basic Safety And
Essential Performance — Collateral Standard: Radiation Protection In Diagnostic X-Ray Equipment
IEC 60695-2-11, Fire Hazard Testing — Part 2-11: Glowing/Hot-Wire Based Test Methods — Glow-Wire
Flammability Test Method for End-Products (GWEPT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org
ISO 15253:2021(E)
3.1
low vision device
apparatus that alters or enhances the image viewed by a person having low vision
3.1.1
optical low vision device
optical device
lens or lens system, prism, or mirror, or combination of such optical components, that alters image
characteristics, such as vergence, size, and/or position
Note 1 to entry: Image relocation using a prism, whether ground in or temporary (e.g., Fresnel), is commonly
expressed in centimetres per metre or prism dioptres.
Note 2 to entry: Image relocation using a mirror is commonly expressed in degrees.
3.1.2
electro-optical low vision device
opto-electronic low vision device
electro-optical device
device or system that produces an altered or enhanced image through the interaction between light
from the object and an electronic system
Note 1 to entry: The device minimally consists of a camera and a monitor or display, but can contain additional
components such as a computer, display control interface, projector, speakers, tactile output, narrow-beam light
source, scanner, and software.
Note 2 to entry: In addition to computer-based systems, common configurations and terms for electro-optical
devices are video magnifier and closed-circuit television (CCTV), with which the image is displayed or projected
at some distance removed from the user’s spectacle plane, and head-mounted (also known as head-up) display,
with which the image is presented on a display at or near the user’s spectacle plane or projected directly into the
user’s eye.
3.1.3
filter
tinted lens
optical component that absorbs and/or reflects light in order to reduce the amount of light transmitted
to the user’s eye
3.1.3.1
neutral density filter
filter (3.1.3) designed to reduce the amount of light by the same percentage for each wavelength across
the visible spectrum
3.1.3.2
coloured tint
filter (3.1.3) that selectively reduces the amount of light transmitted for some wavelengths relative to
that transmitted for other wavelengths
Note 1 to entry: Examples of coloured tints include cut-off, bandpass, and notch filters.
3.2
magnification
ratio between a dimension of the image when a low vision device (3.1) is in use and the corresponding
dimension when the object is viewed without the device
Note 1 to entry: Dimension can be angular or linear.
2 © ISO 2021 – All rights reserved

ISO 15253:2021(E)
3.2.1
angular magnification
ratio of the angle subtended by the image of the object when viewed using a low vision device (3.1) to the
angle subtended by the object alone at a viewing point of reference, such as the entrance pupil of the eye
Note 1 to entry: Angular magnification is used primarily for afocal telescopic low vision devices. It also applies in
part to magnifiers that are positioned at distances removed from the spectacle plane.
3.3
magnifier
lens system designed to change the size of the image of a near object
Note 1 to entry: The magnifier can be a simple single element or a compound multiple-element system.
3.3.1
hand magnifier
hand-held magnifier
magnifier (3.3) intended to be positioned and supported by the user's hand and without artificial
support
3.3.2
stand magnifier
magnifier (3.3) in which a support positions the optical system at a fixed or adjustable distance from
the object to be viewed
3.3.3
head-mounted magnifier
magnifier (3.3) mounted in a device that is supported on the head
3.3.4
spectacle-mounted magnifier
magnifier (3.3) mounted in a device that attaches to a spectacle frame
3.3.5
spectacle magnifier
spectacle microscope
spectacle lenses having greater power for near focus than found in typical spectacle corrections,
creating retinal image magnification primarily by allowing for relative distance magnification
Note 1 to entry: In addition to relative distance magnification, some usually small amount of magnification can
result from the parameters of the lens, such as base curve, centre thickness, and refractive index.
3.4
telescope
optical system composed of two separated lenses (or lens systems), the objective and the eyepiece, that
forms a magnified image of a distant object when the eyepiece is the higher powered lens (or system)
Note 1 to entry: In its afocal adjustment, the second (back) focal point of the objective lies at the first (front)
focal point of the eyepiece, so that light from a distant object, entering the objective with zero vergence, exits the
eyepiece with zero vergence. This is the condition for a user wearing full correction for refractive error viewing a
very distant object clearly through the telescope.
Note 2 to entry: A telescope provides angular magnification, which in its afocal adjustment can be calculated by
the negative of the ratio of the equivalent power of the eyepiece to the equivalent power of the objective.
3.4.1
entrance pupil diameter
clear aperture of the telescopic objective
Note 1 to entry: Entrance pupil diameter is expressed in millimetres.
ISO 15253:2021(E)
3.4.2
focusable telescope
telescope for which the separation between the objective and eyepiece can be changed to compensate
for a range of object distances and/or to compensate for uncorrected spherical refractive error
3.5
telemicroscope
near-vision telescope
telescope adapted for viewing near or intermediate objects
3.5.1
reading cap
positive optical element placed in front of the telescopic objective to adapt the device for viewing a near
or intermediate object
Note 1 to entry: Reading cap power is expressed in dioptres.
Note 2 to entry: In a fixed-focus afocal telescope, the reading cap is a removable lens.
Note 3 to entry: In a fixed-focus telemicroscope, the reading cap is incorporated into the objective power.
Note 4 to entry: In a focusable telescope, a portion of the objective power functions as the reading cap. This
reduces the objective power that remains, thus creating a “new” afocal telescope with slightly greater angular
magnification.
3.6
field expander
reverse telescope
minifier
device that reduces the apparent field of view so that it is smaller than the user’s unaided field of view
Note 1 to entry: Apparent field of view is the angle subtended by the field as viewed through a telescope.
3.7
spatial resolution
smallest separation between two details in the object for which they can be recognised as being
separate under a given set of conditions
3.8
field of view
extent of the object plane visible through, or imaged by, a device
Note 1 to entry: See entries below for definitions of field of view for specific types of devices.
3.8.1
resolvable field of view
field of view within which the device is capable of resolving required details
3.9 Parameters for magnifiers
3.9.1
optical dimensions
zone of optical dimensions
optical zone of magnifier
linear size of the lens of a magnifier that is visible when mounted
Note 1 to entry: Optical dimensions are expressed in millimetres.
3.9.2
magnifier optical axis
line connecting the centres of curvature of the surfaces of an optical system, along which there is
symmetry and zero induced prism
4 © ISO 2021 – All rights reserved

ISO 15253:2021(E)
3.9.3
equivalent focal length
distance between a focal point and the corresponding principal plane, measured along the optical axis
Note 1 to entry: See Figure 1.
Note 2 to entry: First focal length is measured from the first principal plane to the first (front) focal point.
Note 3 to entry: Second focal length is measured from the second principal plane to the second (back) focal point.
3.9.4
equivalent power
reciprocal of the equivalent focal length in air measured in metres
Note 1 to entry: Equivalent power is expressed in dioptres, or reciprocal metres.
Key
1 first focal length F first (front) focal point
2 second focal length F’ second (back) focal point
H first principal plane
H’ second principal plane
Figure 1 — Illustration of focal lengths
3.9.5
magnifier working distance
distance between the front vertex of the magnifier and the object being viewed
Note 1 to entry: See Figure 2.
3.9.6
exit image distance
vertex image distance
distance between the back vertex of the magnifier and the virtual image formed by the magnifier when
the object is placed in the designated position
Note 1 to entry: See Figure 2.
Note 2 to entry: Exit image distance is especially useful for stand magnifiers.
3.9.7
viewing distance
distance between the image formed by the magnifier and the spectacle plane of the user
Note 1 to entry: See Figure 2.
ISO 15253:2021(E)
Key
1 object plane y object size
2 image plane y’ image size
3 spectacle plane
4 working distance
5 exit image distance
6 viewing distance
Figure 2 — Illustration of object plane, image plane, spectacle plane, working distance, exit
image distance and viewing distance for magnifiers
3.9.8
transverse magnification
TM
lateral magnification
enlargement ratio
ER
ratio of the linear image size to the corresponding linear object size, both measured perpendicular to
the optical axis of the magnifier
Note 1 to entry: Transverse magnification is used primarily for magnifiers, especially stand magnifiers.
Note 2 to entry: Referring to Figure 2, transverse magnification can be calculated with the equation TM = y’/y.
3.9.9
lateral variation of magnification
distortion
change in magnification as distance from the optical axis increases
Note 1 to entry: For converging (plus) lenses with an aperture behind the lens, such as the pupil of the user’s eye,
the magnification change is positive, resulting in pincushion distortion.
Note 2 to entry: For diverging (minus) lenses with an aperture behind the lens, such as the pupil of the user’s eye,
the magnification change is negative, resulting in barrel distortion.
Note 3 to entry: If the aperture of the system is placed in front of the lens (that is, the user’s pupil is not the limiting
aperture), a plus lens will produce barrel distortion while a minus lens will produce pincushion distortion.
6 © ISO 2021 – All rights reserved

ISO 15253:2021(E)
3.9.10
nominal magnification
effective magnification
M
nominal
ratio of the retinal image size with zero exit image vergence when using the magnifier to the retinal
image size when the object is viewed at the reference seeing distance without the magnifier
Note 1 to entry: Reference seeing distance is the distance between the spectacle plane and the object or image
observed that is assumed to be the closest that a typical corrected eye can focus clearly and comfortably.
Note 2 to entry: Exit image vergence, expressed in dioptres, is the reciprocal of the exit image distance measured
in metres.
Note 3 to entry: Nominal magnification can be calculated from the product of the reference seeing distance, in
metres, and the equivalent power, in dioptres.
EXAMPLE With a reference seeing distance of 0,25 m the nominal magnification is calculated from the
formula
M = 0,25 F = F/4.
nominal
3.9.11
trade magnification
conventional magnification
M
trade
ratio of the retinal image size when the magnifier is placed at the spectacle plane, and the object is
placed such that the image is at the reference seeing distance, to the retinal image size when the object
is viewed at the reference seeing distance without the magnifier
Note 1 to entry: Trade magnification can be calculated from the nominal magnification using the formula:
M = M + 1
trade nominal
3.9.12
linear field of view
field of view at the viewing distance stated by the manufacturer
Note 1 to entry: Linear field of view is expressed in millimetres at a specified viewing distance.
3.10 Parameters for telescopes, telemicroscopes and minifying field expanders
3.10.1
telescope optical axis
line on which the elements or components of an optical system are centred
Note 1 to entry: A lens system that incorporates a prism or mirror can have a folded or nonlinear optical axis.
3.10.2
telescope object field of view
field of view at the working distance specified by the manufacturer
Note 1 to entry: Object field of view is denoted in either metres at a specified distance or degrees.
3.10.3
telescope working distance
distance between the telescope objective and the object being viewed
ISO 15253:2021(E)
3.10.4
telemicroscope equivalent power
product of the reading cap power and telescope magnification
Note 1 to entry: Equivalent power is expressed in dioptres, or reciprocal metres.
3.11 Parameters for electro-optical devices
3.11.1
display size
horizontal and vertical dimensions of the display within which the image is visible, i.e., active area
Note 1 to entry: Many displays are labelled by their oblique size, i.e., linear distance between diagonally opposite
corners.
3.11.2
electro-optical device working distance
working space
distance between the front of the camera of the system and the object being imaged
3.11.3
system resolution
spatial resolution of the system, limited by the component that has the lowest resolution
Note 1 to entry: System resolution is expressed in pixels horizontal by pixels vertical.
Note 2 to entry: Spatial resolution for the user will depend on and vary with display size and working distance.
Thus, it typically cannot be set or controlled by the manufacturer.
3.11.4
display magnification
ratio between any linear dimension of the displayed image and the corresponding dimension of the
object
3.11.5
electro-optical device object field of view
field of view that is imaged by the system for conditions of use stated by the manufacturer
Note 1 to entry: Object field of view is expressed in millimetres.
3.11.6
contrast ratio
ratio of the luminance of the brightest colour (e.g., white) to that of the darkest colour (e.g., black)
produced by a display
Note 1 to entry: Contrast ratio is commonly normalised to a minimum value of 1 and reported, for example, as
300:1.
Note 2 to entry: Displays capable of producing zero luminance would have a contrast ratio of infinity.
3.11.8
object table
XY table
device used to support and position the object being viewed
8 © ISO 2021 – All rights reserved

ISO 15253:2021(E)
3.11.9
text to speech system
text to speech device
video magnifier or CCTV that incorporates optical character recognition (OCR) to convert text to audio
output recognizable to the user as speech
Note 1 to entry: Optical character recognition (OCR) is the conversion of typed, printed, or handwritten text into
machine-encoded text, which can then be used in other applications, such as searchable text, speech, and braille.
4 Classification
4.1 Optical devices
4.1.1 Distance vision
Telescopes, field expanders, and devices for image relocation.
4.1.2 Near and intermediate vision
Magnifiers, telemicroscopes, focusable telescopes, and devices for image relocation.
4.1.3 Retinal illumination reduction or contrast enhancement
Neutral density filter, coloured tint, cut-off, bandpass, and notch filters.
4.2 Electro-optical devices
Electronic systems for viewing objects at distance, intermediate, and/or near. Such devices capture
images and display them on a screen either directly or indirectly via projection, or by projecting directly
into the eye.
5 Requirements
5.1 General
5.1.1 Risk assessment and management
Manufacturers shall assess and manage potential risks that may pose harm to the user using, when
applicable, the steps provided in ISO 14971, ISO 62366-1, and IEC 60601-1.
A device that projects an image directly onto the retina shall meet the requirements of ISO 15004-2. The
manufacturer shall assess and manage potential light hazards related to intended long-term repetitive
daily use of the device.
5.1.2 Materials
Materials comprising the device and its components shall conform to the relevant clauses of ISO 15004-1
and, when applicable, ISO 12870.
5.1.3 Dimensions and weight
The dimensions and weight of each component of the device shall be within ±10 % of the stated values.
ISO 15253:2021(E)
5.1.4 Flammability/Ignitability
When the device is tested as described in IEC 60695-2-11, there shall be no continued combustion after
withdrawal of the test rod.
5.1.5 Resistance to perspiration
Parts of the device that are normally in contact with skin, as on the face and head, and that are covered
by the scope of ISO 12870 shall meet the relevant requirements of ISO 12870.
5.1.6 Robustness
Spectacle magnifiers and spectacle- and head-mounted magnifiers shall meet the relevant requirements
of ISO 12870 and ISO 14889.
Tinted lenses and filters shall meet the relevant requirements of ISO 12312-1.
If appropriate, electro-optical devices shall meet the relevant requirements of IEC 60601-1-3.
5.1.7 Resistance to drop
If claims are made that the device is drop-resistant, the manufacturer shall state the conditions under
which this claim is made and the conditions of testing.
5.2 Optical devices
5.2.1 Spatial resolution
The resolution of the optical device shall be measured at an object contrast of not less than 80 %.
5.2.1.1 Devices designed for near/intermediate use
When tested in accordance with 6.2.1, the device shall resolve a target that consists of line pairs
measuring not more than 0,233 mm per pair (0,116 mm per element) within the central 70 % of the
linear field of view, for targets having white light meeting the specifications of CIE standard illuminant
D65 within the illuminance range of 750 lx to 1 000 lx with the device used as intended by the
manufacturer.
NOTE 1 0,116 mm is the element size that subtends 1´ of arc at a distance of 400 mm.
NOTE 2 For stand magnifiers it is recommended that the manufacturer state the range of viewing distances
for which the magnifier meets the resolution requirement and also state the range of resolvable fields of view for
this range of viewing distances.
5.2.1.2 Devices designed for distance vision
When tested in accordance with 6.2.1, the device shall resolve targets consisting of line pairs subtending
an angle of 2´ (or less) having elements subtending an angle of 1´ (or less) within the central 70 % of
the linear field of view, or the central 10°, whichever is the smaller. If these requirements exceed the
diffraction limit of the device, then the smallest resolvable element spacing, specified in cycles per
degree, shall not be less than 50 % of the diffraction limit for monochromatic light at 555 nm within the
above specified area. The telescope shall meet these requirements at the limits of the claimed working
range.
5.2.2 Equivalent power (applies to optical devices designed for near or intermediate use)
The equivalent power of a spherically powered magnifier or fixed-focus telemicroscope/near-vision
telescope measured along the optical axis shall be stated by the manufacturer and shall be within ±5 %
of the value stated.
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ISO 15253:2021(E)
If unwanted astigmatism is present, the difference in power between the two meridians shall be
within ±2,5 %.
For magnifiers designed with significantly different powers in two meridians, the deviation of the
equivalent power from the stated value in each of the two principal meridians shall be within ±2,5 % of
the equivalent power.
5.2.3 Magnification
5.2.3.1 Nominal magnification or trade magnification (applies to all magnifiers)
If nominal magnification or trade magnification is stated by the manufacturer in addition to equivalent
power, it shall be within ±5 % of the value stated.
5.2.3.2 Transverse magnification (applies to stand magnifiers)
If the transverse magnification of the stand magnifier is stated by the manufacturer, it shall be
measured along the optical axis and shall be within ±5 % of the value stated.
It is strongly recommended that transverse magnification be provided for stand magnifiers, preferably
by marking, but at least including it in product information, since this is important for calculating the
equivalent power of a stand magnifier/near addition power combination clinically.
5.2.3.3 Angular magnification (applies to telescopes designed for distance use)
The angular magnification of the afocal telescope measured along the optical axis shall be within ±5 %
of the value stated.
5.2.3.4 Uniformity of magnification
When the linear field of view of the device is examined as described in 6.2.1, the variation in
magnification over the central 70 % of the linear field shall comply with Table 1 or Table 2 as applicable.
The manufacturer shall state the method of testing.
Table 1 — Magnifiers/near telescopes/devices designed for near/intermed
...