EN ISO 13666:2019
(Main)Ophthalmic optics - Spectacle lenses - Vocabulary (ISO 13666:2019)
Ophthalmic optics - Spectacle lenses - Vocabulary (ISO 13666:2019)
This document defines terms relating to ophthalmic optics, specifically to blanks, finished spectacle lenses and fitting purposes.
Terms relating to processes and material for fabrication and surface treatment (other than some specific terms relating to coatings), and terms relating to defects in materials and after optical processing are given in ISO 9802.
Augenoptik - Brillengläser - Begriffe (ISO 13666:2019)
Dieses Dokument definiert Begriffe der Augenoptik, insbesondere Begriffe für Blanks, fertige Brillengläser und deren Anpassung.
Begriffe betreffend die Herstellungsverfahren und Ausgangsmaterialien sowie die Oberflächenbehandlung (abgesehen von einigen Begriffen betreffend Schichten) und Begriffe betreffend Fehler im Material und nach der optischen Verarbeitung sind in ISO 9802 angegeben.
Optique ophtalmique - Verres de lunettes - Vocabulaire (ISO 13666:2019)
Le présent document définit les termes relatifs à l'optique ophtalmique, notamment aux palets, aux verres de lunettes finis et au domaine du montage.
Les termes relatifs aux processus et aux matériaux de fabrication et de traitement de surface (autres que les quelques termes relatifs aux revêtements particuliers), ainsi que les termes relatifs aux défauts des matériaux et au traitement post-optique, figurent dans l'ISO 9802.
Očesna optika - Stekla očal - Slovar (ISO 13666:2019)
Ta dokument določa izraze v zvezi z očesno optiko, ki so specifični za stekla, dokončana stekla
očal in za namene vstavljanja.
Izrazi v zvezi s postopki in materialom za izdelavo ter površinsko obdelavo (razen specifičnih izrazov v zvezi s premazi) in izrazi v zvezi s poškodbami materialov ter po optični obdelavi so podani v standardu ISO 9802.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-maj-2019
1DGRPHãþD
SIST EN ISO 13666:2013
2þHVQDRSWLND6WHNODRþDO6ORYDU ,62
Ophthalmic optics - Spectacle lenses - Vocabulary (ISO 13666:2019)
Augenoptik - Brillengläser - Vokabular (ISO 13666:2019)
Optique ophtalmique - Verres de lunettes - Vocabulaire (ISO 13666:2019)
Ta slovenski standard je istoveten z: EN ISO 13666:2019
ICS:
01.040.11 Zdravstveno varstvo Health care technology
(Slovarji) (Vocabularies)
11.040.70 Oftalmološka oprema Ophthalmic equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 13666
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2019
EUROPÄISCHE NORM
ICS 01.040.11; 11.040.70 Supersedes EN ISO 13666:2012
English Version
Ophthalmic optics - Spectacle lenses - Vocabulary (ISO
13666:2019)
Optique ophtalmique - Verres de lunettes - Vocabulaire Augenoptik - Brillengläser - Vokabular (ISO
(ISO 13666:2019) 13666:2019)
This European Standard was approved by CEN on 24 October 2018.
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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, 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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13666:2019 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 13666:2019) 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 September 2019, and conflicting national standards
shall be withdrawn at the latest by September 2019.
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 13666:2012.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 13666:2019 has been approved by CEN as EN ISO 13666:2019 without any modification.
INTERNATIONAL ISO
STANDARD 13666
Third edition
2019-02
Ophthalmic optics — Spectacle lenses
— Vocabulary
Optique ophtalmique — Verres de lunettes — Vocabulaire
Reference number
ISO 13666:2019(E)
©
ISO 2019
ISO 13666:2019(E)
© ISO 2019
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: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
ISO 13666:2019(E)
Contents Page
Foreword .iv
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Basic optics . 1
3.2 Lenses and their dispensing . 4
3.3 Lens materials .14
3.4 Lens surfaces .15
3.5 Classification according to function .17
3.6 Classification according to form . .18
3.7 Classification according to type of lens .19
3.8 Classification according to state of manufacture .20
3.9 Measurement of dioptric properties of lenses .22
3.10 Focal properties .24
3.11 Prismatic properties .28
3.12 Spherical-power lenses .30
3.13 Astigmatic-power lenses .30
3.14 Lenticular lenses .32
3.15 General descriptive terms for multifocal and power-variation lenses .33
3.16 Optical centration and focal properties of multifocal and power-variation lenses .37
3.17 Transmittance, reflectance and polarization .39
3.18 Coatings .46
Annex A (informative) Spectral weighting functions and spectral distributions .48
Bibliography .59
Alphabetical index .60
ISO 13666:2019(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 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 7,
Ophthalmic optics and instruments.
This third edition cancels and replaces the second edition (ISO 13666:2012), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Since the document is for spectacle lens terminology, the single word “lens” rather than “spectacle
lens” is used throughout the document.
— This revision has resulted in a few terms that were no longer used in lens standards or in
communications between participants in the lens manufacturing and dispensing chain being
deleted. The terms that were in clause 17 have been either moved or incorporated into earlier terms.
— Over 50 % of terms and definitions have been revised. In some cases, this is as little as changing
the order of synonyms for the term, to significant changes in the wording of definitions or notes to
entry, but without change of meaning.
— The meaning of vertex distance has been altered so that it now refers to the horizontal distance
between the back surface of the lens and the apex of the cornea, measured with the eyes in the
primary position. The plane of the lens shape is now defined as being the plane containing the
vertical centreline parallel to the horizontal centreline of the individual lens based on the apex of
the groove instead of being based on the plane tangential to the demonstration lens. The design
reference points are where the manufacturer's specifications apply, while the reference points are
where the lenses are to be verified. For single-vision and most multifocal lenses, these are the same.
The previous distinction for a multifocal lens, where the distance design reference point was usually
the centre of the semi-finished lens blank (now called simply "blank") while the distance reference
point was usually the intended position of the optical centre of the distance portion after surfacing,
has been removed — they are the design reference point or simply the reference points of the blank
and the finished lens.
iv © ISO 2019 – All rights reserved
ISO 13666:2019(E)
— The term "as-worn" corrected dioptric power has been replaced by the term verification power — this
word explains its purpose better, and is clarified by a new definition. Shape magnification has been
replaced by the more general spectacle magnification.
— The following additional terms have been added:
— as-worn pantoscopic angle;
— centration point position;
— darkened state;
— degressive-power blank;
— distance power;
— faded state;
— fused multifocal lens;
— infrared transmittance;
— lens shape;
— mean sphere;
— near power;
— near reference point;
— ordered distance prismatic effect;
— ordered near prismatic effect;
— ordered power;
— ordered prismatic effect;
— position-specific single-vision lens;
— power-variation blank;
— power-variation lens;
— power-variation surface;
— presbyopia;
— prescribed power;
— primary reference point;
— reference point;
— secondary reference point;
— segment bottom;
— segment top;
— solar blue-light transmittance;
— spectacle magnification;
— spherical equivalent power;
ISO 13666:2019(E)
— traffic signal light;
— ultraviolet transmittance;
— variation power;
— verification power.
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.
vi © ISO 2019 – All rights reserved
ISO 13666:2019(E)
Introduction
This new edition of ISO 13666 has been prepared in line with the new provisions of ISO/IEC Directives,
Part 2. This led to a renumbering of all terms. All the terms are now in Clause 3, “Terms and definitions”,
so the previous subsections have been made into full subclauses to simplify the numbering. "Notes"
have been replaced by "notes to entry" — these can be normative, as opposed to notes in specification
standards which are informative.
General considerations in the interpretation of this vocabulary document are:
— since this document relates to spectacle lenses, the simple word 'lens' or 'lenses' is generally used
throughout (except where definitions have been quoted from other standards) instead of 'spectacle
lens' or 'spectacle lenses'. The term "spectacle lens" is defined in 3.5.2. When “lens” means a lens in
general, including but not restricted to spectacle lenses, it is not italicized in the text. When “lens”
means a spectacle lens, the word “lens” is put in italics.
−1
— the unit of focusing power, expressed in reciprocal metres (m ), of a lens or surface is the dioptre.
See 3.10.1 for a complete definition;
— the unit of prismatic power is the prism dioptre (Δ), expressed in centimetres per metre (cm/m).
See 3.11.11 for a complete definition;
— to simplify definitions and the understanding of the optics of ophthalmic lenses, aberrations of
lenses and prisms are ignored in definitions except when specifically mentioned;
— definitions are classified according to subject;
— deprecated: Some obsolete terms are listed for convenience, but are indicated as "DEPRECATED"
and should not be used;
— in this document, the word "normal" (to a surface) means a line that is at 90° to the plane that is
tangential to the surface at the point of interest, i.e. is perdendicular to the surface at that point.
INTERNATIONAL STANDARD ISO 13666:2019(E)
Ophthalmic optics — Spectacle lenses — Vocabulary
1 Scope
This document defines terms relating to ophthalmic optics, specifically to blanks, finished spectacle
lenses and fitting purposes.
Terms relating to processes and material for fabrication and surface treatment (other than some specific
terms relating to coatings), and terms relating to defects in materials and after optical processing are
given in ISO 9802.
2 Normative references
There are no normative references in this document.
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/
NOTE CIE International Lighting Vocabulary CIE S 017: 2011 is available at http: //eilv .cie .co .at/.
3.1 Basic optics
3.1.1
optical radiation
electromagnetic radiation at wavelengths between the region of transition to X-rays (λ ≈ 1 nm) and the
region of transition to radio waves (λ ≈ 1 mm)
[SOURCE: CIE S 017:2011, 17-848]
3.1.2
visible radiation
light
any optical radiation (3.1.1) capable of causing a visual sensation directly
Note 1 to entry: The limits of photo-detection depend upon the amount of radiant power reaching the retina and
the responsivity of the observer.
Note 2 to entry: ISO 20473 specifies the spectral range of visible radiation to have a lower limit of 380 nm and
an upper limit of 780 nm for application to Optics and Photonics standards. These limits apply to spectacle lens
(3.5.2) standards.
[SOURCE: CIE S 017:2011, 17-1402, modified — the note has been deleted, while notes 1 and 2 to entry
have been added.]
ISO 13666:2019(E)
3.1.3
ultraviolet radiation
DEPRECATED: ultraviolet
optical radiation (3.1.1) for which the wavelengths are shorter than those for visible radiation (3.1.2)
Note 1 to entry: ISO 20473 specifies the spectral range of ultraviolet radiation for the application to Optics and
Photonics standards and subdivides the UV range into:
— UV-A: 315 nm to 380 nm;
— UV-B: 280 nm to 315 nm;
— UV-C: 100 nm to 280 nm.
Other health and safety disciplines define UV-A as 315 nm to 400 nm.
[SOURCE: CIE S 017:2011, 17-1367, modified —The notes have been deleted while note 1 to entry has
been added.]
3.1.4
infrared radiation
DEPRECATED: infrared
optical radiation (3.1.1) for which the wavelengths are longer than those for visible radiation (3.1.2),
from 780 nm to 1 mm
Note 1 to entry: For infrared radiation, the range between 780 nm and 1 mm is commonly subdivided into:
— IR-A: 780 nm to 1 400 nm;
— IR-B: 1,4 µm to 3 µm;
— IR-C: 3 µm to 1 mm.
Note 2 to entry: These limits are also specified in ISO 20473.
Note 3 to entry: The solar infrared radiation spectrum at sea level extends to about 2 000 nm.
Note 4 to entry: The range of infrared radiation emitted by the source and reaching the lens shall be considered in
the design of an infrared radiation-absorbing material.
[SOURCE: CIE S 017:2011, 17-580, modified — Notes 2, 3 and 4 to entry have been added.]
3.1.5
refractive index
n(λ)
ratio of the velocity of propagation of monochromatic radiation of the wavelength (λ) in vacuum to its
velocity of propagation in the medium
Note 1 to entry: For technical applications, the refractive index is given against air instead of against vacuum.
Note 2 to entry: The wavelengths to be used for the characterization of optical materials (3.3.1), all kinds of
optical systems and instruments, and spectacle lenses (3.5.2), are specified in ISO 7944.
3.1.6
chromatic dispersion
change in the refractive index (3.1.5) of monochromatic radiation in a medium as a function of the
frequency of the radiation
Note 1 to entry: The chromatic dispersion gives rise to chromatic aberration in a lens made from dispersive
materials.
2 © ISO 2019 – All rights reserved
ISO 13666:2019(E)
3.1.7
Abbe number
υ υ
d, e
DEPRECATED: constringence
DEPRECATED: V-value
indicator of the chromatic dispersion (3.1.6) of an optical material (3.3.1) or component
Note 1 to entry: The Abbe number can be calculated as either:
n −1
d
υ =
d
nn−
FC
where
n is the refractive index of the yellow helium d-line (wavelength: 587,56 nm);
d
n is the refractive index of the blue hydrogen F-line (wavelength: 486,13 nm); and
F
n is the refractive index of the red hydrogen C-line (wavelength: 656,27 nm);
C
or
n −1
e
υ =
e
nn−
FC′′
where
n is the refractive index of the green mercury e-line (wavelength: 546,07 nm);
e
n is the refractive index of the blue cadmium F′-line (wavelength: 479,99 nm); and
F′
n is the refractive index of the red cadmium C′-line (wavelength: 643,85 nm).
C′
Note 2 to entry: These reference wavelengths are given in ISO 7944:1998.
3.1.8
optical axis
straight line joining the centres of curvature of both surfaces of a lens (3.5.2)
Note 1 to entry: This line is normal to both optical surfaces so light can pass along it undeviated.
Note 2 to entry: For lenses (3.5.2) with strong prismatic power (3.11.10), the optical axis can lie outside the area
of the lens.
Note 3 to entry: Power-variation lenses (3.7.7) do not have a true optical axis.
3.1.9
vertex
point of intersection of the optical axis (3.1.8) with a surface of a lens (3.5.2)
3.1.10
power
capacity of a lens (3.5.2) or optical surface to change the curvature or direction of incident wavefronts
by refraction
3.1.11
focal point
image point conjugate to an infinitely distant object point on the optical axis (3.1.8)
ISO 13666:2019(E)
3.1.12
bioactinic
exhibiting or referring to bioactinism (3.1.13)
3.1.13
bioactinism
property of optical radiation (3.1.1) that enables it to cause chemical changes to biological tissues
3.1.14
presbyopia
reduction in the ability to accommodate through normal ageing, resulting in the inability to focus at
usual near distances with any ametropia corrected
3.2 Lenses and their dispensing
3.2.1
boxed lens system
boxing system
system of measurement and definitions based on the rectangle formed by the horizontal and vertical
tangents to the extremities of the lens shape (3.2.2)
Note 1 to entry: Because the horizontal and vertical tangents might not be in the same plane, for a lens (3.5.2) this
can be thought of as an orthogonal projection onto a plane parallel to the front surface (3.2.13) at its boxed centre
(3.2.5).
3.2.2
lens shape
outline of the edged lens (3.8.9) periphery in its intended orientation
Note 1 to entry: The nasal side should be indicated.
Note 2 to entry: Lens shape refers to the shape of lenses (3.5.2) that fit the frame with:
— for a lens having a bevelled edge, the outermost edge of the lens, the lens having a bevel which includes a
symmetrical angle of 120° and a bevel width greater than the width of the groove in the front;
— for a lens having a flat or grooved edge, the outermost edge of the lens.
3.2.3
horizontal centreline
horizontal straight line located at an equal distance from the two horizontal tangents of the boxed lens
system (3.2.1)
[SOURCE: ISO 8624:2011, A.1, modified — The words "horizontal straight" have been added and the
word "(boxing)" has been deleted.]
3.2.4
vertical centreline
vertical straight line located at an equal distance from the vertical sides of the rectangular box that
circumscribes the lens shape (3.2.2)
[SOURCE: ISO 8624:2011, A.2, modified — The words "vertical straight" have been added and the word
"which" has been changed to "that".]
3.2.5
boxed centre
C
intersection of the horizontal centreline (3.2.3) and the vertical centreline (3.2.4) of the rectangular box
that circumscribes the lens shape (3.2.2)
Note 1 to entry: This term is applied to spectacle frames and to the edged lens (3.8.9).
4 © ISO 2019 – All rights reserved
ISO 13666:2019(E)
[SOURCE: ISO 8624:2011, 2.1, modified — The word "which" has been replaced by "that" and note 1 to
entry has been added.]
3.2.6
geometrical centre
geometric centre
intersection of the horizontal centreline (3.2.3) and vertical centreline (3.2.4) of the rectangular box that
circumscribes the shape of the blank (3.8.1) or uncut lens (3.8.8)
3.2.7
nominal size
d
n
dimension indicated by the manufacturer
Note 1 to entry: For round blanks (3.8.1) or lenses (3.5.2), the size is given as the diameter. Otherwise, the
horizontal and vertical dimensions are given.
3.2.8
effective size
d
e
actual physical dimension
Note 1 to entry: For round blanks (3.8.1) or lenses (3.5.2), the size is given as the diameter. Otherwise, the
horizontal and vertical dimensions are given.
3.2.9
usable size
d
u
dimension of the area that is optically usable
Note 1 to entry: For round blanks (3.8.1) or lenses (3.5.2), the size is given as the diameter. Otherwise, the
horizontal and vertical dimensions are given.
3.2.10
horizontal axis
zero direction through a reference point (3.2.19) on the lens (3.5.2) for the specification of cylinder axes
(3.13.8) and prism base settings (3.11.7) as defined in ISO 8429
3.2.11
meridian
each plane that contains the centre(s) of curvature of the surface
Note 1 to entry: See also principal meridians (3.4.5).
3.2.12
meridian
each plane that contains the optical axis (3.1.8) of the lens (3.5.2)
3.2.13
front surface
surface of the lens (3.5.2) intended to be fitted away from the eye
3.2.14
back surface
surface of the lens (3.5.2) intended to be fitted nearer to the eye
3.2.15
optical centre
intersection of the optical axis (3.1.8) with the front surface (3.2.13) of a lens (3.5.2)
ISO 13666:2019(E)
3.2.16
design reference point
point, stipulated by the manufacturer, on the finished surface of a blank (3.8.1) or on the front surface
(3.2.13) of the finished lens (3.8.7) at which the design specifications apply
EXAMPLE Distance design reference point and near design reference point.
3.2.17
distance design reference point
point, stipulated by the manufacturer, on the front surface (3.2.13) of a finished lens (3.8.7) or on the
finished surface of a blank (3.8.1) at which the design specifications for the distance portion (3.15.1) apply
3.2.18
near design reference point
point, stipulated by the manufacturer, on the front surface (3.2.13) of a finished lens (3.8.7) or on the
finished surface of a blank (3.8.1) at which the design specifications for the near portion (3.15.3) apply
3.2.19
reference point
point, stipulated by the manufacturer, on the front surface (3.2.13) of a finished lens (3.8.7) or on the
finished surface of a blank (3.8.1) at which the verification power (3.10.15) of a specific portion applies
Note 1 to entry: Unless a verification power (3.10.15) is stated, the power is the nominal or ordered power (3.10.14).
See note 3 to entry to verification power.
Note 2 to entry: This point can, in some circumstances, differ from the respective design reference point (3.2.16).
Note 3 to entry: For power-variation lenses (3.7.7), focal power (3.10.2) and prismatic power (3.11.10) are measured
at different reference points.
EXAMPLE Distance reference point and near reference point.
3.2.20
distance reference point
major reference point
point on the front surface (3.2.13) of the lens (3.5.2) at which the verification power (3.10.15) for the
distance portion (3.15.1) applies
Note 1 to entry: This point can, in some circumstances, be different from the distance design reference point
(3.2.17).
Note 2 to entry: Unless a verification power (3.10.15) is stated, the power is the nominal or ordered power (3.10.14).
See note 3 to entry to verification power.
3.2.21
near reference point
point on the front surface (3.2.13) of the lens (3.5.2) at which the verification power (3.10.15) for the near
portion (3.15.3) applies
Note 1 to entry: This point can, in some circumstances, be different from the near design reference point (3.2.18).
Note 2 to entry: Unless a verification power (3.10.15) is stated, the power is the nominal or ordered power (3.10.14).
See note 3 to entry to verification power.
3.2.22
primary reference point
point on the front surface (3.2.13) of a power-variation lens (3.7.7) at which the verification power
(3.10.15) for the designed primary use of the lens (3.5.2) applies
Note 1 to entry: All power-variation lenses have a primary reference point.
Note 2 to entry: For example, the primary reference point for a progressive-power lens (3.7.8) is the distance
reference point (3.2.20) and for a degressive-power lens (3.7.9) is the near reference point (3.2.21).
6 © ISO 2019 – All rights reserved
ISO 13666:2019(E)
[SOURCE: ISO 21987:2017, 3.5]
3.2.23
secondary reference point
point on the front surface (3.2.13) of a power-variation lens (3.7.7) at which the verification power
(3.10.15) for the designed secondary use of the lens (3.5.2) applies
Note 1 to entry: Some power-variation lenses (3.7.7) can have a secondary reference point that is used for the
determination of the addition power (3.16.3) or variation power (3.16.4).
Note 2 to entry: For example, the secondary reference point for a progressive-power lens (3.7.8) is the near reference
point (3.2.21).
[SOURCE: ISO 21987:2017, 3.6]
3.2.24
line of sight en: US
visual axis en: GB
ray path from the point of interest (i.e. point of fixation) in object space to the centre of the entrance
pupil of the eye and its continuation in image space from the centre of the exit pupil to the retinal point
of fixation (generally the foveola)
Note 1 to entry: These two parts of the ray path are distinct and separate segments.
3.2.25
primary direction
direction of the line of sight (3.2.24), usually taken to be the horizontal, to an object at an infinite
distance measured with habitual head and body posture when looking straight ahead in unaided vision
3.2.26
primary position
position of the eye when looking in the primary direction (3.2.25)
3.2.27
visual point
point of intersection of the line of sight (3.2.24) with the back surface (3.2.14) of a lens (3.5.2)
3.2.28
interpupillary distance
PD
distance between the centres of the pupils when the eyes are in the primary position (3.2.26)
3.2.29
monocular pupillary distance
distance between the centre of the pupil and the mid-line of the bridge of the nose or the spectacle
frame when the eye is in the primary position (3.2.26)
3.2.30
centration point
CP
point with respect to the frame at which the optical centre (3.2.15), distance reference point (3.2.20)
or fitting point (3.2.34) is to be located in the absence of any ordered prismatic effect (3.11.14) and any
prism thinning (3.16.9), or after any such prismatic effect (3.11.9) has been neutralized
Note 1 to entry: Which of these is relevant depends upon the type of lens (3.5.2), for example, the optical centre
(3.2.15) usually applies to a single-vision lens (3.7.1), distance reference point (3.2.20) usually to an aspheric lens
(3.6.8) or multifocal lens (3.7.3) and fitting point (3.2.34) usually to a position-specific single-vision lens (3.7.2) or a
power-variation lens (3.7.7).
ISO 13666:2019(E)
Note 2 to entry: When a lens incorporates prismatic power (3.11.10), a correction should be made to the position
of the centration point (monocular centration distance (3.2.31) and centration point height) when mounting the
lens to compensate for the change in position of the eye. This correction depends on the power of the prismatic
correction needed and the as-worn position (3.2.36). This correction may be done when ordering the lenses or be
done by the manufacturer.
Note 3 to entry: This point can be specified:
— in the plane of the lens shape (3.2.41), by its horizontal (u) and vertical (v) decentrations (3.2.33) from the
boxed centre (3.2.5);
— in the plane of the lens shape, by its horizontal distance (x) from the nasal vertical tangent of the boxed lens
system (3.2.1) and its centration height ( y) above the lower horizontal tangent;
— in the plane of the spectacle front (3.2.42), by its monocular centration distance (z) and centration height ( y)
above the lower horizontal tangent.
For details and sign convention, see Figures 1 and 2.
Note 4 to entry: With the horizontal, a, and vertical, b, boxed lens sizes, the distances mentioned in note 3 to
entry can be computed as u = x – a/2 and v = y – b/2 respectively.
Note 5 to entry: With face form angle α and the boxed centre distance c, the following relation between u and the
monocular centration distance z applies:
cz−2
u=
2cosα
where u is positive if the centration point is nasal relative to the vertical centreline (3.2.4).
Key
1 vertical centreline
2 horizontal centreline
C C right/left boxed centre
R L
P P right/left centration point
R L
N N right/left near visual point
R L
x x horizontal distance of right/left centration point
R L
y y right/left centration point height/fitting point height
R L
u u horizontal decentration of the right/left centration point position/fitting point position
R L
ν v vertical decentration of right/left centration point position/fitting point position
R L
a horizontal boxed lens size
b vertical boxed lens size
Figure 1 — Terms relating to the centration/fitting point, measured in the planes of the lens
shapes
8 © ISO 2019 – All rights reserved
ISO 13666:2019(E)
3.2.31
centration distance
CD
required horizontal distance between the centration points (3.2.30) of a pair of mounted lenses (3.5.2)
Note 1 to entry: The centration distance can be specified by monocular values, measured from the assumed
centreline of the bridge of the spectacle frame, i.e. the spectacle frame's vertical symmetry axis.
Note 2 to entry: For distance vision, in the absence of any horizontal prismatic effect (3.11.9), the interpupillary
distance (3.2.28) can be taken to be the centration distance. For intermediate and near prescriptions, the
centration distance needs to be adjusted for binocular convergence.
Note 3 to entry: See z in Figure 2.
3.2.32
optical centre distance
OCD
distance between centres
DEPRECATED: optical PD
horizontal distance between the optical centres (3.2.15) of a pair of mounted lenses (3.5.2), with any
ordered prismatic effect (3.11.14) being neutralized
Note 1 to entry: The optical centre distance is not applicable to power-variation lenses (3.7.7).
3.2.33
decentration
displacement of the centration point (3.2.30) from the boxed centre (3.2.5) of the shape of the edged
lens (3.8.9)
Note 1 to entry: See u and v in Figure 1.
ISO 13666:2019(E)
Key
1 vertical symmetry axis
2 horizontal centreline
C C right/left boxed centre
R L
P P right/left centration point
R L
N N right/left near visual point
R L
z z right/left monocular centration distance
R L
q q right/left monocular near visual point distance
R L
y y right/left centration point height/fitting point height
R L
ν v vertical decentration of right/left centration point
R L
c boxed centre distance
d distance between lenses
Figure 2 — Terms relating to the centration/fitting point, measured in the plane of the
spectacle front
3.2.34
fitting point
point on the front surface (3.2.13) of a lens (3.5.2) or blank (3.8.1) stipulated by the manufacturer for
positioning the lens in front of the eye
3.2.35
centration point position
fitting point mounting position
vertical and horizontal fitting distances and directions of the centration point (3.2.30) or fitting point
(3.2.34) respectively from the boxed centre (3.2.5), measured in the plane of the lens shape (3.2.41)
Note 1 to entry: The fitting point mounting position relates to the ordered mounting position in the frame, not the
mounted value or the height of the fitting point (3.2.34) in relation to the permanent alignment reference markings
(3.15.25).
Note 2 to entry: See v , v , u and u in Figure 1.
R L R L
3.2.36
as-worn position
position of wear
position, including orientation, of the lenses (3.5.2) relative to the eyes and face during wear
Note 1 to entry: The as-worn position shall be measured with the habitual head and body posture. For distance
vision, this is usually measured in the primary position (3.2.26) when looking straight ahead in unaided vision.
10 © ISO 2019 – All rights reserved
ISO 13666:2019(E)
3.2.37
as-worn pantoscopic angle
position of wear pantoscopic angle
vertical angle between the horizontal and the perpendicular to a reference line passing through the
apex of the grooves of the upper and lower rims of the frame in the vertical plane containing the primary
direction (3.2.25)
Note 1 to entry: The as-worn position (3.2.36) shall be measured with the habitual head and body posture.
For distance vision, this is usually measured in the primary position (3.2.26) when looking straight ahead in
unaided vision.
Note 2 to entry: The angle is regarded as positive if the lower part of the lens (3.5.2) lies closer to the face than
the upper.
Note 3 to entry: For rimless and semi-rimless frames, a comparable measurement needs to be made.
Note 4 to entry: See Figure 3.
Key
1 as-worn pantoscopic angle
2 primary direction, taken to be horizontal
3 reference line through the apex of the grooves of the rims in a vertical plane passing through the pupil
4 perpendicular to the reference line
5 vertex distance
6 right angle (90°)
Figure 3 — Illustration of as-worn pantoscopic angle and vertex distance
3.2.38
as-worn face form angle
as-worn wrap angle
position of wear face form angle
position of wear wrap angle
horizontal angle between the primary direction (3.2.25) and the perpendicular to a reference line
passing through the apex of the grooves of the nasal and temporal rims of the frame in the horizontal
plane containing the primary direction
Note 1 to entry: The right or left as-worn face form angle is regarded as positive if the temporal side of the plane of
the right or left lens shape (3.2.41) is posterior to the nasal side.
ISO 13666:2019(E)
Note 2 to entry: The as-worn position (3.2.36) shall be measured with the habitual head and body posture.
For distance vision, this is usually measured in the primary position (3.2.26) when looking straight ahead in
unaided vision.
Note 3 to entry: For rimless and semi-rimless frames, a comparable measurement needs to be made.
Note 4 to entry: See Figure 4.
Key
1 primary direction
2 reference line
3 perpendicular to the reference line
4 right and left as-worn face form angles
5 right angle (90°)
Figure 4 — Illustration of as-worn face form angle
3.2.39
face form angle
wrap angle
angle between the plane of the spectacle front (3.2.42) and the right plane of the lens shape (3.2.41) or of
the left plane of the lens shape
Note 1 to entry: The right or left face form angle is regarded as positive if the temporal side of the plane of the lens
shape (3.2.41) is posterior to the nasal side.
Note 2 to entry: The face form angles are often measured and specified as the average of the right and left angles,
but the frame can be adjusted for a specific wearer so that they differ, and the right and left angles should then be
specified.
Note 3 to entry: This angle relates to the frame, not the as-worn position (3.2.36).
Note 4 to entry: See 6 and 6 in Figure 5.
R L
12 © ISO 2019 – All rights reserved
ISO 13666:2019(E)
Key
C C right/left boxed centre
R L
1 plane of the spectacle front
2 XY plane, perpendicular to plane 1
3 3 right/left vertical centrelines
R L
4 4 right/left horizontal centrelines
R L
5 vertical symmetry axis
6 6 face form angle, measured in plane 2
R L
Figure 5 — 3D schematic representation of the plane of the spectacle front and the planes of the
lens shapes of a frame
3.2.40
vertex distance
horizontal distance between the back surface (3.2.14) of the lens (3.5.2) and the apex of the cornea,
measured with the eyes in the primary position (3.2.26)
Note 1 to entry: See Figure 3.
3.2.41
plane of the lens shape
plane that contains the vertical centreline (3.2.4) and is parallel to the horizontal centreline (3.2.3) of the
individual lens (3.5.2)
Note 1 to entry: The vertical (3.2.4) and horizontal centrelines (3.2.3) are based on the apex of the groove. For
rimless and semi-rimless frames, the centre of the edge of an afocal lens (3.6.3) mounted in the frame is to be
regarded as equivalent.
Note 2 to entry: See Figure 5.
3.2.42
plane of the spectacle front
plane that contains the vertical centrelines (3.2.4) of the right and left boxed lens shapes (3.2.2)
Note 1 to entry: This will be an approximation if the two centrelines are not parallel to each other.
ISO 13666:2019(E)
Note 2 to entry: See Figure 5.
[SOURCE: ISO 8624:2011, A.11, modified — Note 2 to entry has been added.]
3.2.43
working distance
distance from the reference plane to the object plane
Note 1 to entry: By ophthalmic convention, this reference plane is usually taken to be the plane of the spectacle
front (3.2.42).
3.2.44
near vision distance
working distance (3.2.43) with the individual’s habitual near working plane as the object
...
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