SIST EN ISO 11979-2:2025

SLOVENSKI STANDARD
01-januar-2025
Nadomešča:
SIST EN ISO 11979-2:2014
Očesni vsadki (implantati) - Intraokularne leče - 2. del: Optične lastnosti in
preskusne metode (ISO 11979-2:2024)
Ophthalmic implants - Intraocular lenses - Part 2: Optical properties and test methods
(ISO 11979-2:2024)
Ophthalmische Implantate - Intraokularlinsen - Teil 2: Optische Eigenschaften und
Prüfverfahren (ISO 11979-2:2024)
Implants ophtalmiques - Lentilles intraoculaires - Partie 2: Propriétés optiques et
méthodes d'essai (ISO 11979-2:2024)
Ta slovenski standard je istoveten z: EN ISO 11979-2:2024
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 11979-2
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2024
EUROPÄISCHE NORM
ICS 11.040.70 Supersedes EN ISO 11979-2:2014
English Version
Ophthalmic implants - Intraocular lenses - Part 2: Optical
properties and test methods (ISO 11979-2:2024)
Implants ophtalmiques - Lentilles intraoculaires - Ophthalmische Implantate - Intraokularlinsen - Teil 2:
Partie 2: Propriétés optiques et méthodes d'essai (ISO Optische Eigenschaften und Prüfverfahren (ISO 11979-
11979-2:2024) 2:2024)
This European Standard was approved by CEN on 1 November 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 11979-2:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 11979-2:2024) 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 May 2025, and conflicting national standards shall be
withdrawn at the latest by May 2025.
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 11979-2:2014.
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 11979-2:2024 has been approved by CEN as EN ISO 11979-2:2024 without any
modification.
International
Standard
ISO 11979-2
Third edition
Ophthalmic implants — Intraocular
2024-10
lenses —
Part 2:
Optical properties and test methods
Implants ophtalmiques — Lentilles intraoculaires —
Partie 2: Propriétés optiques et méthodes d'essai
Reference number
ISO 11979-2:2024(en) © ISO 2024

ISO 11979-2:2024(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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 11979-2:2024(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 1
4.1 General .1
4.2 Dioptric power .2
4.2.1 General .2
4.2.2 Dioptric power for toric IOL (TIOL) .2
4.2.3 Dioptric power for simultaneous vision IOL (SVIOL) .2
4.2.4 Dioptric power for accommodating IOL (AIOL) .3
4.3 Imaging quality .3
4.3.1 General .3
4.3.2 Monofocal IOL .4
4.3.3 Toric IOL (TIOL) .4
4.3.4 Simultaneous vision IOL (SVIOL) .4
4.3.5 Accommodating IOL (AIOL) .4
4.3.6 Combination of optical principles .4
4.3.7 Exceptions .4
4.4 Optical characterization .5
4.5 Spectral transmittance .5
4.5.1 Measurement of spectral transmittance .5
4.5.2 Cut-off wavelength .5
Annex A (normative) Measurement of dioptric power . 6
Annex B (normative) Measurement of MTF . 14
Annex C (normative) Optical characterization .18
Bibliography .21

iii
ISO 11979-2:2024(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, 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 third edition cancels and replaces the second edition (ISO 11979-2:2014), which has been technically
revised.
The main changes are as follows:
— A new category of simultaneous vision IOLs (SVIOL) is introduced for non-accommodating
lenses that provide simultaneous vision at multiple distances. It includes multifocal IOLs (MIOL),
extended depth of focus IOLs (EDF), and full visual range IOLs (FVR).
— Dioptric power, imaging quality, and characterization clauses and annexes were modified to include
requirements for SVIOLs.
-1 -1
— Respective units of mm and degree were adopted for linear and angular spatial frequencies per
ISO 9334.
— The resolution efficiency and associated annex have been removed from this document due to
advancements in optical designs and the availability of modulation transfer function (MTF) imaging
quality measurement methods.
— A new Annex C with associated requirements for all IOL categories has been added.
— Clarified description of UV cut-off wavelength.
— New references were added to the Bibliography.
A list of all parts in the ISO 11979 series can be found on the ISO website.
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 11979-2:2024(en)
Introduction
This document initially addressed monofocal IOLs and now includes the optical requirements and test
methods for monofocal, toric, simultaneous vision, and accommodating IOLs. This document generally
provides specific test methods and requirements connected to the optical function of intraocular lenses. In
some cases, test methods do not have specified requirements, including:
— the spectral transmittance test that provides information related to UV transmission and potential
exposure situations, e.g. when using laser light sources for diagnosis and treatment;
— optical characterization testing that informs potential optical design risks and guides potential clinical
investigation design.
The specified dioptric power and imaging quality limits result from the analysis of extensive interlaboratory
testing of the original spherical monofocal IOLs. Based on these studies, the respective dioptric power
repeatability and reproducibility were about 0,5 % and 1 %, respectively, of the dioptric power as described
in Reference [1]. Additionally, for IOLs in the 10 D to 30 D range, the respective expected imaging quality
repeatability and reproducibility were 0,09 and 0,16 modulation transfer function values as described
in Reference [2]. For other non-monofocal IOL designs, manufacturers should utilize model-specific
repeatability and reproducibility precision limits to establish reliable final release criteria.
During the interlaboratory testing, some problems were encountered with measuring dioptric power, as
described in Reference [1]. Specifically, the accuracy in determining dioptric power has an error that is
not negligible in relation to the half dioptre steps in which intraocular lenses are commonly labelled. The
dioptric power tolerances take this fact into account. Hence the limits set may lead to some overlap into the
next labelled power, especially for high dioptre lenses. Reference [1] further discusses this subject.
Historically, imaging quality was tested using either
a) Air Force target-based resolution efficiency, or
b) MTF using a minimal spherical aberration model eye, or
c) a manufacturer-defined spherical aberration model eye using modulation transfer function (MTF)
testing.
Since the test method with Air Force target-based resolution efficiency is not optimal for quantifying image
contrast, and better methods using MTF measurements have become mainstream in the industry, Air Force
target-based resolution efficiency is not included in this revision as a reference method. The model eye
with manufacturer-defined spherical aberration includes the option of having a model eye with minimal
spherical aberration. Therefore, the original model eye with minimal spherical aberration is removed from
this document. For lenses that have already been approved using the measurements in the previous edition,
it is not necessary to retest these lens models with the method in this document.
Annex B describes a test method used to establish quality criteria for IOLs. The quality criteria assure
consistent IOL optical quality. This document also includes a new normative optical characterization text
(see Annex C), that is meant to provide preclinical assessments to inform of risks and benefits associated
with the optical design and guide the design of the potential clinical investigation. The additional optical
characterization is required only for lens models to be approved after publication of this document.

v
International Standard ISO 11979-2:2024(en)
Ophthalmic implants — Intraocular lenses —
Part 2:
Optical properties and test methods
1 Scope
This document specifies requirements and test methods for certain optical properties of intraocular lenses
(IOLs) with monofocal, toric, simultaneous vision, and/or accommodative optics. The generic descriptor
‘IOL’ used throughout this document also includes phakic intraocular lenses (PIOL).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
the 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 9334, Optics and photonics — Optical transfer function — Definitions and mathematical relationships
ISO 9335, Optics and photonics — Optical transfer function — Principles and procedures of measurement
ISO 11979-1, Ophthalmic implants — Intraocular lenses — Part 1: Vocabulary
ISO 11979-4, Ophthalmic implants — Intraocular lenses — Part 4: Labelling and information
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11979-1 and ISO 9334 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Requirements
4.1 General
The manufacturer shall assure that the entire range of available powers meets the specifications herein. All
optical properties apply at in situ conditions, either by being measured at simulated in situ conditions, or
being measured at other conditions and then corrected to in situ conditions.
For IOLs where the optic is intended to be deformed during implantation, it shall be demonstrated that
dioptric power and imaging quality are retained at in situ or equivalent conditions following surgical
[3]
manipulation and recovery. See ISO 11979-3 for more details.
The test methods described in this document are reference methods. Alternative methods that produce
equivalent results to those obtained with the reference methods may be used if the manufacturer can
demonstrate that the IOLs meet the minimum dioptric power and imaging quality requirements.

ISO 11979-2:2024(en)
For rotationally symmetric IOLs the manufacturer shall assure that lenses meet the requirements in all
meridians, for example by selecting an arbitrary meridian for measurement.
4.2 Dioptric power
4.2.1 General
The base power of lenses as stated by the manufacturer in the IOL labelling per ISO 11979-4 shall be
within the tolerance limits specified in Table 1. Manufacturers shall consider measurement precision when
establishing IOL release specifications.
Table 1 — Tolerance limits on spherical dioptric power, S
Tolerance limits on spherical
a
Nominal base power
dioptric power
D
D
0 ≤ |S| ≤ 15 ±0,3
15 < |S| ≤ 25 ±0,4
25 < |S| ≤ 30 ±0,5
30 < |S| ±1,0
a
The dioptric power ranges apply to positive and negative dioptric powers.
4.2.2 Dioptric power for toric IOL (TIOL)
When determined by any of the methods in Annex A, the spherical equivalent (SE) power shall be within
the tolerance limits for dioptric power specified in Table 1. Additionally, the cylindrical power calculated as
the absolute difference between the powers of the meridian of highest dioptric power and the meridian of
lowest dioptric power shall be within the cylindrical power tolerance limits specified in Table 2.
Table 2 — Tolerance limits on cylindrical dioptric power, C
Tolerance limits on cylindri- Tolerance limits on cylindri-
Nominal cylindrical dioptric
cal dioptric power cal dioptric power
power
D D
D
SE < 25 D SE ≥ 25 D
0 < C ≤ 2,5 ±0,3 ±0,4
2,5 < C ≤ 4,5 ±0,4 ±0,4
4,5 < C ±0,5 ±0,5
The TIOL shall have a physical axis indicator such as a mark, engraving, or label that aligns with the meridian
of lowest dioptric power and is visible to the surgeon during implantation. The angle difference between the
physical axis indicator and the meridian with the lowest dioptric power shall be less than or equal to 5,0°.
4.2.3 Dioptric power for simultaneous vision IOL (SVIOL)
Methods A.3 to A.4 can be applied to SVIOLs for determining the far power and any designed distinct addition
power(s). The dioptric power of the far power shall be within the tolerance limits specified in Table 1, and
the dioptric power of designed distinct addition power(s) shall be within the tolerances in Table 3. For
SVIOLs that do not have designed distinct addition powers, the manufacturer shall develop MTF through-
focus response specifications per 4.3.4.

ISO 11979-2:2024(en)
Table 3 — Tolerance limits on addition dioptric power, A
Tolerance limits on addition Tolerance limits on addition
Nominal addition dioptric
dioptric power dioptric power
power
D D
D
far power < 25 D far power ≥ 25 D
0 < A ≤ 2,5 ±0,3 ±0,4
2,5 < A ≤ 4,5 ±0,4 ±0,4
4,5 < A ±0,5 ±0,5
4.2.4 Dioptric power for accommodating IOL (AIOL)
The power associated with the far power configuration of an AIOL shall be determined by one of the
methods in Annex A. When determined by one of these methods, the dioptric power tolerances specified in
Table 1 shall apply to the power associated with the far power configuration of the AIOL. The dioptric power
response of the lens or system in the eye shall be determined in a theoretical or laboratory eye model that
simulates the intended accommodating mechanism of action.
4.3 Imaging quality
4.3.1 General
Reported imaging quality is dependent upon compatibility between the optical design, manufactured lens
quality, and conditions that are used to evaluate optical performance. Imaging quality shall be specified
in relation to theoretical lens performance in terms of a modulation transfer function (MTF) value at one
or more specified spatial frequencies or the area under the MTF curve between two spatial frequencies
for a given aperture. Manufacturers shall consider measurement precision when establishing IOL release
specifications.
A method for measuring MTF and example model eye specifications are given in Annex B. Alternatively,
the manufacturer can specify an equivalent method or model eye with optical properties for the intended
use and design. In this case, the model eye and the method shall be fully described, and a justification for
the use thereof be provided. The imaging quality specifications apply to all available powers unless stated
otherwise.
NOTE 1 The test apertures given in 4.3 and in Annexes A, B, and C represent the exposed central area of the IOL
under test.
NOTE 2 Throughout this document, optical resolution is specified using spatial frequencies that are presented in
-1
cycles per millimetre (mm ). Alternatively, equivalent values for the generally accepted vision science convention of
-1
cycles per degree (degree ) can be used:
-1 -1
— where the document specifies 100 mm , alternatively 30 degree can be used;
-1 -1
— where the document specifies 50 mm , alternatively 15 degree can be used;
-1 -1
— where the document specifies 25 mm , alternatively 7,5 degree can be used.
-1 -1
If conversion back from these values in degree to mm is needed for different lens powers, the following
approximative conversion can be used, as shown in Formula (1)
with:
-1
— SF = spatial frequency, expressed in degree ;
-1
— sf = spatial frequency, expressed in mm ;
— EFL(P) = effective focal length of the model eye, with an IOL with power P (in D) in place;
— so that EFL(20) = EFL of the model eye with an IOL of 20 D.
Then:
ISO 11979-2:2024(en)
sf()PP =×EFLE()20 //FL() SF 03, (1)
-1 -1
Other methods for converting between mm and degree are acceptable if justification can be provided.
4.3.2 Monofocal IOL
−1
In accordance with Annex B with a 3 mm aperture, the MTF value shall at 100 mm meet either of the two
requirements given below:
a) ≥0,43;
b) ≥70 % of the theoretically attainable MTF for the nominal lens design, but in any case ≥0,28.
4.3.3 Toric IOL (TIOL)
In accordance with Annex B using a model eye with IOL configuration, the MTF requirements described in
4.3.2 shall apply to the meridians of highest and lowest dioptric power.
4.3.4 Simultaneous vision IOL (SVIOL)
The SVIOL imaging quality specifications shall be evaluated by MTF testing using the methods and eye
model described in Annex B for the following conditions:
-1 -1
a) for far dioptric power, record MTF at 25 mm and a second spatial frequency in the range from 50 mm
-1
to 100 mm for small and large apertures. The small aperture diameter shall be selected from 2,0 mm,
2,5 mm, or 3,0 mm. The large aperture diameter shall be selected from 4,0 mm, 4,5 mm, or 5,0 mm.
b) for lens designs that have one or more designed distinct addition powers, for each addition power,
-1 -1 -1
record MTF at 25 mm and a second spatial frequency in the range from 50 mm to 100 mm for a
small aperture. The small aperture diameter shall be selected from 2,0 mm, 2,5 mm or 3,0 mm.
The manufacturer shall have the option of setting the minimum MTF specification based on the area under
the curve between the two spatial frequencies or on the MTF value for each individual spatial frequency. A
specification describing the MTF through-focus response shall be developed for designs with no designed
distinct addition power(s). The MTF shall be ≥70 % of the theoretically attainable MTF for the lens design
under the defined test conditions.
4.3.5 Accommodating IOL (AIOL)
The requirements given in 4.3.2 shall apply at the far power configuration and configurations associated
with the designed range of accommodation. Measurements shall be obtained in 0,5 D or smaller increments
over this range if applicable.
4.3.6 Combination of optical principles
Lenses combining optical principles shall meet applicable test requirements such as described in the
following examples.
For toric simultaneous vision and toric accommodating lenses, the general imaging requirements in 4.3.3
apply along with the test requirements in 4.3.4 and 4.3.5, respectively.
For simultaneous vision accommodating lenses the imaging test requirements of 4.3.4 and 4.3.5 apply.
4.3.7 Exceptions
If the criteria specified in 4.3.2 through 4.3.6, for reasons of theoretical limitation, cannot be applied to
negative, low, or high power lenses in conjunction with the model eye described, the manufacturer shall
justify any alternative spatial frequencies and criteria.

ISO 11979-2:2024(en)
4.4 Optical characterization
Optical characterization shall be performed in accordance with the methods described in Annex C. The
optical characterization contributes to the assessment of potential risks and benefits associated with
the optical design and shall serve as input for the design of a potential clinical investigation. The optical
characterization does not have quantitative pass/fail criteria.
4.5 Spectral transmittance
4.5.1 Measurement of spectral transmittance
The spectral transmittance in the range 300 nm to 1 100 nm shall be recorded by a spectrophotometer
with a 3 mm aperture under simulated in situ conditions or corrected for specular reflection if measured
in air. The measurement should be accurate to ±2 % transmittance and the resolution should be ≤5 nm. The
test specimen shall be either an actual IOL or a flat facsimile of the IOL optic material, having a thickness
equal to the centre thickness of a 20 D spherical equivalent IOL and having undergone the same production
treatment as the finished IOL including sterilization.
NOTE For toric lenses, an IOL of SE = 20 D with lowest available cylinder or equivalent non-toric IOL can be used.
4.5.2 Cut-off wavelength
The UV cut-off is the wavelength in nanometres at which the spectral transmission is ≤ 10 % when measured
according to 4.5.1.
NOTE Guidance for measuring spectral transmittance can be found in ISO 18369-3; see Reference [4].

ISO 11979-2:2024(en)
Annex A
(normative)
Measurement of dioptric power
A.1 General
Multiple methods of determining IOL dioptric power are given below. Where applicable, the specific methods
and requirements for monofocal, toric, simultaneous vision, and accommodating IOL measurements are
described in this annex.
For all IOLs, the value of dioptric power is defined at in situ conditions (see ISO 11979-1) for a light source
that has a peak wavelength within ±10 nm of 546 nm having a full width at half maximum of 20 nm or less.
For the methods in A.3 and A.4, an aperture of 3,0 mm ± 0,1 mm in diameter is used.
NOTE 1 For more details about optical measurement and calculations, see Reference [5] or similar textbooks on optics.
NOTE 2 A modified bench (e.g. additional converging lens, a microscope objective of appropriate numerical
aperture, etc.) can be used to quantify the focal length of negative and low dioptric power IOLs.
A.2 Determination of dioptric power by calculation from measured dimensions
A.2.1 Procedure
Measure the optical surface radii of curvature over a region of approximately 3 mm diameter using a radius
meter, interferometer, or optical coherence tomograph (OCT), see Reference [6]. Measure the lens thickness
with a micrometer or equivalent device. Calculate the dioptric power, using Formula (A.1):
DD=+Dt−()/nD D (A.1)
fb cIOL fb
under in situ conditions, where
D is the dioptric power of the IOL;
D is the dioptric power of the front surface of the IOL;
f
D is the dioptric power of the back surface of the IOL;
b
t is the central thickness, in metres, of the IOL;
c
n is the refractive index of the IOL optic material at in situ conditions.
IOL
NOTE 1 Formula (A.1) is often referred to as the “thick lens equation”.
NOTE 2 In general, the value of n is influenced by temperature and water uptake by the IOL optic material.
IOL
Calculate D from Formula (A.2):
f
Dn=−()nr/ (A.2)
fIOL medf
ISO 11979-2:2024(en)
where
n is the refractive index of the surrounding medium;
med
r is the surface radius of curvature, in metres, of the front surface of the IOL.
f
Calculate D from Formula (A.3):
b
Dn=−nr/ (A.3)
()
bmed IOLb
where r is the surface radius of curvature, in metres, of the back surface of the IOL.
b
NOTE 3 With respect to the incidence of light, a convex radius is positive and a concave radius is negative.
NOTE 4 These formulae assume that there is exact alignment of front and back surfaces along the optical axis.
[7]
NOTE 5 ISO 18369-4 describes a method that can be used to determine n , which should be known to the third
IOL
decimal place.
NOTE 6 If the lens material is flexible, appropriate care is taken when measuring the two lens surfaces to ensure
that the two surface measurements are consistent with each other. Any flexing of the lens between the measurements
of the two surfaces will affect the results.
Use n = 1,336, and the dimensions and refractive index of the IOL under in situ conditions to obtain the
med
dioptric power in situ, D , from Formula (A.1).
aq
If the measured dimensions and the refractive index of the IOL were not obtained under in situ conditions,
apply proper corrections to calculate the corresponding values at in situ conditions.
A.2.2 Applicability
This method as described is only applicable to rotationally symmetric spherical monofocal IOL designs.
A.3 Determination of dioptric power by calculation from measured back focal length
or effective focal length
A.3.1 Principle
The method described in A.3 assumes measurement in air but is applicable to measurement at simulated in
situ conditions with proper adjustments.
The back focal length (BFL) is the distance from the back vertex of the IOL to the focal point with parallel light
incident on-axis upon the IOL. This method has historically been used to measure monofocal lenses in air.
The effective focal length (EFL) is the distance from the second principal plane to the focal point with parallel
light incident on-axis upon the IOL. EFL can be measured with an optical bench equipped with a nodal slide,
see Reference [5].
Both methods can be used when appropriate corrections are made as described below.
NOTE 1 The position of the focal point is dependent on the spatial frequency used to find the focal point. It is
normally not coincident with the paraxial focal point of the lens under measurement if there is spherical aberration.
The focus found is often referred to as “best focus”.
NOTE 2 BFL, EFL, and the corrections are all vector quantities. The positive direction is that of the incident light
and is measured along the optical axis.

ISO 11979-2:2024(en)
A.3.2 Apparatus
Optical bench, e.g. as illustrated in Figure A.1, having the following features:
a) a collimator achromat that is virtually free from aberrations in combination with the light source used,
having a focal length preferably at least 10 times that of the IOL being measured;
b) a spatial frequency target such as the U.S. Air Force 1951 Resolution Target, see Reference [8], diffusely
illuminated by a light source in the focal plane of the collimator;
c) an aperture stop of 3,0 mm ± 0,1 mm placed maximally 3 mm in front of the IOL being measured;
d) a surrounding medium of air;
e) a microscope objective with a numerical aperture greater than that of the test system and capable of
magnifying ×10 to ×20;
f) an eye-piece magnifying about ×10.
NOTE 1 To measure a focal length longer than the testing apparatus, an additional converging lens or microscope
objective of appropriate numerical aperture can be used.
NOTE 2 It is a matter of convenience whether to use a straight bench or employ a mirror as illustrated in Figure A.1.
The microscope is connected to a position measuring device so that its position along the optical axis can be
determined with a precision of 0,01 mm.
A.3.3 Procedure
A.3.3.1 Mount the IOL on the optical bench just behind the 3 mm aperture.
A.3.3.2 Focus the microscope at the back surface of the IOL and note the position of the microscope.
A.3.3.3 Focus the microscope at the image of the target and note the position of the microscope. The
distance from the back vertex of the IOL to the focal point is the back focal length, BFL, of the IOL.
If focusing is done using a USAF target element, the group/element that is closest to 0,3 of the IOL's MTF
cut-off frequency shall be used. Otherwise, focusing is done at a spatial frequency of 0,3 ± 0,04 of the cut-off
frequency of the IOL. The procedure given here assumes that measurement is done in air at normal ambient
conditions of a laboratory. The calculations assume that the dimensions of the IOL are not appreciably
different under in situ conditions. Should that not be the case, BFL is measured with the IOL under simulated
in situ conditions, with appropriate changes in the calculations.
A.3.3.4 Calculate the distance from the back vertex of the IOL to the back principal plane of the IOL, as
given by Formula (A.4):
''
−=AH ()DD//⋅()nn ⋅t (A.4)
2 fmed IOLc
where n = 1 for measurement in air.
med
NOTE 1 A H” is a vector that can be positive or negative depending on lens shape. The quantity -A H” is added to
2 2
BFL as correction.
NOTE 2 This correction does not apply to EFL.

ISO 11979-2:2024(en)
Key
1 eyepiece 7 mirror
2 microscope body 8 target
3 microscope objective 9 dichroic filter
4 IOL 10 condenser lens system
5 3,0 mm aperture 11 light source
6 collimator doublet 12 retro-reflecting mirror
Figure A.1 — Optical bench with IOL
A.3.3.5 Calculate the longitudinal spherical aberration (LSA) as the vector from the paraxial focal point to
the intersection of a meridional ray at the pupillary margin with the optical axis, and determine the defocus
(Def ) caused by spherical aberration, as given by Formula (A.5):
−=DefL− SA/2 (A.5)
where LSA is the longitudinal spherical aberration, expressed in millimetres. It is permissible under
this document to calculate Def by other procedures, such as those available in optical design calculation

ISO 11979-2:2024(en)
programmes and raytrace software, provided that the correctness of the programme has been verified.
Alternatively, the LSA may be measured directly by wavefront mapping technology.
NOTE 1 The user of this document is referred to the optics literature for methods on how to calculate LSA, see
Reference [5].
NOTE 2 Def is a vector that can be positive or negative. The quantity −Def is added to BFL (or EFL) as a correction.
A.3.3.6 If BFL is measured, calculate EFL as follows in Formula (A.6):
EFLB=−FL AH'' (A.6)
Calculate the paraxial focal length f (in metres), using Formula (A.7):
fE=−FL Def (A.7)
A.3.3.7 Paraxial focal length, f, is converted to dioptric power, D (in reciprocal metres), using Formula (A.8):
Dn= / f (A.8)
med
where n = 1.
med
A.3.3.8 Compute the conversion ratio, Q, using Formula (A.9):
QD= /D (A.9)
aq,nom air,nom
where D and D are the respective dioptric powers calculated in situ and air from Formulae (A.1),
aq,nom air,nom
(A.2) and (A.3) using nominal dimensions for the IOL, n = 1 and the appropriate value for n .
med IOL
A.3.3.9 Finally calculate the dioptric power in situ, D , using Formula (A.10):
aq
DD=⋅Q (A.10)
aq air
NOTE If measurement of BFL (or EFL) is made at simulated in situ conditions, n = 1,336 in Formulae (A.2),
med
(A.3), (A.4) and (A.8). Formula (A.8) then gives directly D .
aq
A.3.4 Applicability
This method is, as described, applicable to rotationally symmetric IOLs.
A.4 Determination of dioptric power from measured magnification
A.4.1 Principle
The concept of lens power relates to the image magnification of a lens. The principle of the focal collimator
to measure magnification to determine dioptric power is given here.
A.4.2 Apparatus
An optical bench such as described in A.3.2 with the following modifications:
a) a target with a measurable repeating pattern such as the U.S. Air Force 1951 Resolution Target
b) an eye-piece with some means, such as a reticle, to measure the corresponding linear dimension in
the image.
ISO 11979-2:2024(en)
A.4.3 Procedure
Determine the linear dimension, h , of the target.
target
Determine the focal length, F, of the collimator.
NOTE 1 These two determinations need not be repeated every time.
NOTE 2 The ratio F/h could be obtained by measurement of calibrated lenses in lieu of the IOL.
target
Mount the IOL on the optical bench just behind the 3 mm aperture.
Focus the microscope on the image and measure the linear dimension, h , in the image.
image
Focusing is done at a spatial frequency of 0,3 ± 0,04 of the cut-off frequency of the IOL.
Calculate the effective focal length (EFL) of the IOL, by using Formula (A.11):
EFLF= /hh⋅ (A.11)
()
target image
Add the spherical aberration corrections from Formula (A.5) to EFL using Formula (A.7) to obtain the
paraxial focal length, f , and continue to calculate the dioptric power in air and aqueous according to
air
Formulae (A.8), (A.9), and (A.10).
A.4.4 Applicability
This method is as described applicable to rotationally symmetric IOLs.
A.5 Determination of dioptric power and error in axis for TIOL
A.5.1 General
For toric IOLs, the methods in this Annex allow the determination of the dioptric power of the principal
meridians with the highest and lowest dioptric power and the measurement of the alignment of the axis
marks with the meridian with the lowest dioptric power.
A.5.2 Without the use of a null lens
For toric IOLs, the dioptric powers in the two principal meridians are determined as follows:
a) If determined in accordance with A.2: calculate the dioptric powers from measured dimensions
(including radii) of the two principal meridians;
b) If determined in accordance with A.3: calculate the dioptric powers from the measured back focal
lengths of the two principal meridians. The principal meridian under measurement and the applied
target are aligned in such a way tha
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