SIST EN ISO 18369-3:2017

SLOVENSKI STANDARD
SIST EN ISO 18369-3:2017
01-november-2017
1DGRPHãþD
SIST EN ISO 18369-3:2006
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Ophthalmic optics - Contact lenses - Part 3: Measurement methods (ISO 18369-3:2017)
Augenoptik - Kontaktlinsen - Teil 3: Messverfahren (ISO 18369-3:2017)
Optique ophtalmique - Lentilles de contact - Partie 3: Méthodes de mesure (ISO 18369-
3:2017)
Ta slovenski standard je istoveten z: EN ISO 18369-3:2017
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
SIST EN ISO 18369-3:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 18369-3:2017

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SIST EN ISO 18369-3:2017


EN ISO 18369-3
EUROPEAN STANDARD

NORME EUROPÉENNE

September 2017
EUROPÄISCHE NORM
ICS 11.040.70 Supersedes EN ISO 18369-3:2006
English Version

Ophthalmic optics - Contact lenses - Part 3: Measurement
methods (ISO 18369-3:2017)
Optique ophtalmique - Lentilles de contact - Partie 3: Augenoptik - Kontaktlinsen - Teil 3: Messverfahren
Méthodes de mesure (ISO 18369-3:2017) (ISO 18369-3:2017)
This European Standard was approved by CEN on 1 July 2017.

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: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 18369-3:2017 E
worldwide for CEN national Members.

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SIST EN ISO 18369-3:2017
EN ISO 18369-3:2017 (E)
Contents Page
European foreword . 3

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SIST EN ISO 18369-3:2017
EN ISO 18369-3:2017 (E)
European foreword
This document (EN ISO 18369-3:2017) 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 March 2018, and conflicting national standards shall
be withdrawn at the latest by March 2018.
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 18369-3:2006.
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 18369-3:2017 has been approved by CEN as EN ISO 18369-3:2017 without any
modification.
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SIST EN ISO 18369-3:2017

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SIST EN ISO 18369-3:2017
INTERNATIONAL ISO
STANDARD 18369-3
Second edition
2017-08
Ophthalmic optics — Contact lenses —
Part 3:
Measurement methods
Optique ophtalmique — Lentilles de contact —
Partie 3: Méthodes de mesure
Reference number
ISO 18369-3:2017(E)
©
ISO 2017

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SIST EN ISO 18369-3:2017
ISO 18369-3:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

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SIST EN ISO 18369-3:2017
ISO 18369-3:2017(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Methods of measurement for contact lenses . 1
4.1 General . 1
4.2 Radius of curvature . 2
4.2.1 General. 2
4.2.2 Optical spherometry (rigid contact lenses) . 3
4.2.3 Sagittal height method . 6
4.3 Label back vertex power .11
4.3.1 General.11
4.3.2 Focimeter specification .11
4.3.3 Calibration .12
4.3.4 Focimeter measurement of rigid lenses .13
4.3.5 Focimeter measurement of hydrogel lenses .13
4.3.6 Measurement of hydrogel contact lenses by immersion in saline .13
4.3.7 Addition power measurement .14
4.4 Diameters and widths .14
4.4.1 Total diameter .14
4.4.2 Zone diameters and widths .19
4.5 Thickness .20
4.5.1 General.20
4.5.2 Dial gauge method .20
4.5.3 Low-force mechanical gauge method .21
4.6 Edge inspection .22
4.7 Determination of inclusions and surface imperfections .22
4.8 Spectral transmittance .23
4.8.1 General.23
4.8.2 Instrument specification, test conditions and procedure .23
4.9 Saline solution for testing .24
4.9.1 General.24
4.9.2 Formulation .24
4.9.3 Preparation procedure .25
4.9.4 Packaging and labelling .25
5 Test report .26
Annex A (informative) Measurement of rigid contact lens curvature using interferometry .27
Annex B (informative) Measurement of label back vertex power of soft contact lenses
immersed in saline using the Moiré deflectometer or Hartmann methods .29
Annex C (informative) Measurement of the radius of curvature of contact lenses using
the ophthalmometer .33
Annex D (informative) Paddle support for focimeters used for power measurements of
contact lenses .38
Bibliography .40
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SIST EN ISO 18369-3:2017
ISO 18369-3:2017(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: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 7, Ophthalmic optics and instruments.
This second edition cancels and replaces the first edition (ISO 18369-3:2006), which has been
technically revised.
A list of all parts in the ISO 18369 series can be found on the ISO website.
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SIST EN ISO 18369-3:2017
INTERNATIONAL STANDARD ISO 18369-3:2017(E)
Ophthalmic optics — Contact lenses —
Part 3:
Measurement methods
1 Scope
This document specifies the methods for measuring the physical and optical properties of contact
lenses specified in ISO 18369-2, i.e. radius of curvature, label back vertex power, diameter, thickness,
inspection of edges, inclusions and surface imperfections and determination of spectral transmittance.
This document also specifies the equilibrating solution and standard saline solution for testing of
contact lenses.
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 3696:1987, Water for analytical laboratory use — Specification and test methods
ISO 9342-1, Optics and optical instruments — Test lenses for calibration of focimeters — Part 1: Test lenses
for focimeters used for measuring spectacle lenses
ISO 18369-1:2017, Ophthalmic optics — Contact lenses — Part 1: Vocabulary, classification system and
recommendations for labelling specifications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18369-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Methods of measurement for contact lenses
4.1 General
Clause 4 specifies methods for measuring finished contact lens parameters.
Clause 4 is applicable to testing laboratories, suppliers and users of contact lens products or services, in
which measurement results are used to demonstrate compliance to specified requirements.
Alternative test methods and equipment may be used provided the accuracy and precision are
equivalent to or more capable than the test methods described.
Each method should be capable of measurement with a precision [repeatability and
[8]
reproducibility (R&R)] of ≤30 % of the allowed tolerance range .
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ISO 18369-3:2017(E)

Lenses should be equilibrated by soaking in standard saline or packaging solution for sufficient time
that the parameter to be measured remain constant within the ability of the method to measure the
parameter.
NOTE The process might be influenced by the nature of the lens material, volume of the solution used for
equilibration and the nature of the solution used to hydrate the lens (if any).
The nature of the equilibration solution (i.e. standard saline solution or packaging solution) and the
equilibration process should be identified in the test report.
Many methods require use of specific temperature ranges and this should be considered when
equilibrating the lenses for testing.
4.2 Radius of curvature
4.2.1 General
There are two generally accepted instruments for determining the radius of curvature of rigid contact
lens surfaces. These are the optical microspherometer (see 4.2.2) and the ophthalmometer with contact
lens attachment.
The ophthalmometer method measures the reflected image size of a target placed at a known distance
in front of a rigid or soft lens surface, and the relationship between curvature and magnification of the
reflected image is then used to determine the back optic zone radius (see Annex C).
For hydrogel contact lenses, sagittal depth can be measured using ultrasonic, mechanical and optical
methods that are available and are applicable to hydrogel contact lens surfaces as indicated in 4.2.3 and
Table 1. Sagittal depth can also be used to determine equivalent radius of curvature.
The sagittal methods are generally not recommended instead of radius measurement for rigid spherical
surfaces because aberration, toricity and other errors are masked during sagitta measurement. Sagittal
depth of rigid aspheric surfaces can be useful.
In addition to these measurement methods, a method using interferometry and applicable to rigid
contact lenses is given in Annex A for information.
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SIST EN ISO 18369-3:2017
ISO 18369-3:2017(E)

Table 1 — Reproducibility values for different test methods
a
Refer to Test method/application Reproducibility, R
4.2.2 Optical spherometry
   Spherical rigid lenses ±0,015 mm in air
Annex C Ophthalmometry
   Spherical rigid lenses ±0,015 mm in air
   Spherical rigid lenses ±0,025 mm in saline solution
   Spherical hydrogel lenses
   (38 % water content, t > 0,1 mm) ±0,050 mm in saline solution
c
4.2.3 Sagittal height method
b
   Hydrogel contact lenses
   38 % water content, t > 0,1 mm ±0,05 mm in saline solution
c
   55 % water content, t > 0,1 mm ±0,10 mm in saline solution
c
c
   70 % water content, t > 0,1 mm ±0,20 mm in saline solution
c
NOTE This table provides reproducibility for spherical rigid lenses because this type of lens was included in the ring test
carried out. However, in general, the values equally apply to aspheric and toric rigid lenses.
a
R is the reproducibility as defined in ISO 18369-1:2017, 3.1.12.9.3.
b
The three water contents given in this table were the ones used to conduct the ring test. For other water content lenses,
extrapolation can be used.
c
The reproducibility is equal to the tolerance and, therefore, the sagittal height method is not relevant for water
contents of 70 % and above.
4.2.2 Optical spherometry (rigid contact lenses)
4.2.2.1 Principle
The microspherometer locates the surface vertex and the aerial image (centre of curvature) with
the Drysdale principle, as described below. The distance between these two points is the radius of
curvature for a spherical surface and is known as the apical radius of curvature for an aspheric surface
derived from a conic section. The microspherometer can be used to measure radii of the two primary
meridians of a rigid toric surface and with a special tilting attachment, eccentric radii can be measured
as found in the toric periphery of a rigid aspheric surface. When the posterior surface is measured, the
back optic zone radius is that which is verified.
The optical microspherometer consists essentially of a microscope fitted with a vertical illuminator. See
Figure 1. Light from the target, T, is reflected down the microscope tube by the semi-silvered mirror, M,
and passes through the microscope objective to form an image of the target at T′. If the focus coincides
with the lens surface, then light is reflected back along the diametrically opposite path to form images
at T and T′′. The image at T′′coincides with the first principle focus of the eyepiece when a sharp image
is seen by the observer [Figure 1 a)]. This is referred to as the “surface image”.
The distance between the microscope and the lens surface is increased by either raising the microscope
or lowering the lens on the microscope stage until the image (T′) formed by the objective coincides
with C (the centre of curvature of the surface). Light from the target T strikes the lens’ surface normally
and is reflected back along its own path to form images at T and T′ as before [Figure 1 b)]. A sharp
image of the target is again seen by the observer. This is referred to as the “aerial image”. The distance
through which the microscope or stage has been moved is equal to the radius (r) of curvature of the
surface. The distance of travel is measured with an analogue or digital distance gauge incorporated in
the instrument.
In the case of a toric test surface, there is a radius of curvature determined in each of two primary
meridians aligned with lines within the illuminated microspherometer target.
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It is also possible to measure the front surface radius of curvature by orienting the lens such that its
front surface is presented to the microscope. In this instance, the aerial image is below the lens, such
that the microscope focus at T′ need be moved down from its initial position at the front surface vertex
in order to make T′ coincide with C.
Key
C centre of curvature of the surface to be measured
T target
T′ image of T at a self-conjugate point
T′′ image of T′ located at the first principal focus of the eyepiece, TM = MT′′
M semi-silvered mirror
r radius of curvature of the surface
Figure 1 — Optical system of a microspherometer
4.2.2.2 Instrument specification
The optical microspherometer shall have an optical microscope fitted with a vertical illuminator and
a target and have a fine focus adjustment. The adjustment control shall allow fine movement of the
microscope or of its stage. The adjustment gauge shall have a linear scale.
The objective lens shall have a minimum magnification of ×6,5 with a numerical aperture of not less
than 0,25. The total magnification shall not be less than ×30. The real image of the target formed by the
microscope shall not be greater than 1,2 mm in diameter.
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ISO 18369-3:2017(E)

The scale interval for the gauge shall not be more than 0,02 mm. The accuracy of the gauge shall be
±0,010 mm for readings for 2,00 mm or more at a temperature of 20 °C to 25 °C. The repeatability of the
gauge (see Note 1 and Note 2) shall be ±0,003 mm.
The gauge mechanism should incorporate some means for eliminating backlash (retrace). If readings
are taken in one direction, this source of error need not be considered.
The illuminated target is typically composed of four lines intersecting radially at the centre, separated
from each other by 45°.
The microspherometer shall include a contact lens holder that is capable of holding the contact lens
surface in a reference plane that is normal to the optic axis of the instrument. The holder shall be
adjustable laterally, such that the vertex of the contact lens surface may be centred with respect to the
axis. The contact lens holder shall allow neutralization of unwanted reflections from the contact lens
surface not being measured.
NOTE 1 The term “gauge” refers to both analogue and digital gauges.
NOTE 2 “Repeatability” means the closeness of agreement between mutually independent test results
obtained under the same conditions.
4.2.2.3 Calibration
Calibration (determining the measuring accuracy) shall be carried out using at least three concave
spherical radius test plates over the range to be tested.
EXAMPLE Three concave spherical radius test plates made from crown glass:
—  Plate 1: 6,30 mm to 6,70 mm;
—  Plate 2: 7,80 mm to 8,20 mm;
—  Plate 3: 9,30 mm to 9,70 mm.
The test plates have radii accurately known to ±0,007 5 mm.
Calibration shall take place at a temperature of 20 °C to 25 °C and after the instrument has had sufficient
time to stabilize.
Mount the first test plate so that the optical axis of the microscope is normal to the test surface. Adjust
the separation of the microscope and stage so that the image of the target is focused on the surface
and a clear image of the target is seen through the microscope. Set the gauge to read zero. Increase the
separation between the microscope and the stage until a second clear image of the target is seen in the
microscope. The microscope and surface now occupy the position seen in Figure 1 b).
Both images shall have appeared in the centre of the field of view. If this does not occur, move the test
surface laterally and/or tilted until this does occur. Record the distance shown on the gauge when the
second image is in focus as the radius of curvature.
Take at least 10 independent measurements (see Note) and calculate the arithmetic mean for each set.
Repeat this procedure for the other two test plates. Plot the results on a calibration curve and use this
to correct the results obtained in 4.2.2.4.
NOTE The term “independent” means that the test plate or lens is to be removed from the instrument, the
instrument zeroed and item remounted between each reading.
4.2.2.4 Measurement method
Carry out the measurements on the test lens in air at 20 °C to 25 °C.
Mount the lens so that the optical axis of the microscope is normal to that part of the lens surface of
which the radius is to be measured. Three independent measurements shall be made. Correct the
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SIST EN ISO 18369-3:2017
ISO 18369-3:2017(E)

arithmetic mean of this set of measurements using the calibration curve obtained in 4.2.2.3 and record
the result to the nearest 0,01 mm.
In the case of a toric surface, the contact lens shall not only be centred, but also rotated such that the two
primary meridians are parallel to lines of the target within the microspherometer. The measurement
procedure described shall be carried out for each of the two primary meridians.
In the case of an aspheric surface, where the apical radius of curvature shall be measured, the procedure
is the same as for a spherical surface with the exception that placement of the surface vertex at the
focus of the microscope has to be more precise. At this point, there shall be no toricity noticeable in the
aerial image.
NOTE 1 The equivalent spherical radius of curvature of an aspheric surface can be determined by
measurement of the sagittal depth (s) of the surface over the optic zone (y) using the methods employed in 4.2.3.
The sagittal depth is converted to an equivalent spherical radiu
...