SIST EN ISO 18369-4:2017
(Main)Ophthalmic optics - Contact lenses - Part 4: Physicochemical properties of contact lens materials (ISO 18369-4:2017)
Ophthalmic optics - Contact lenses - Part 4: Physicochemical properties of contact lens materials (ISO 18369-4:2017)
This document specifies the methods of testing the physicochemical properties of contact lens
materials. These are extraction, rigid lens flexure and breakage, oxygen permeability, refractive index
and water content.
Augenoptik - Kontaktlinsen - Teil 4: Physikalisch-chemische Eigenschaften von Kontaktlinsenmaterialien (ISO 18369-4:2017)
Optique ophtalmique - Lentilles de contact - Partie 4: Propriétés physicochimiques des matériaux des lentilles de contact (ISO 18369-4:2017)
ISO 18369-4:2017 vise à spécifier les méthodes d'essai des propriétés physicochimiques des matériaux des lentilles de contact. Il s'agit en l'occurrence de spécifier l'extraction, la flexion et la rupture des lentilles de contact rigides, la perméabilité à l'oxygène, l'indice de réfraction et la teneur en eau.
Očesna optika - Kontaktne leče - 4. del: Fizikalnokemijske lastnosti materialov za kontaktne leče (ISO 18369-4:2017)
Ta dokument določa metode za preskušanje fizikalno-kemijskih lastnosti materialov za kontaktne leče. Te lastnosti so ekstrakcija, upogibanje in lomljivost trde leče, prepustnost kisika, lomni količnik in vsebnost vode.
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 18369-4:2017
01-november-2017
1DGRPHãþD
SIST EN ISO 18369-4:2006
2þHVQDRSWLND.RQWDNWQHOHþHGHO )L]LNDOQRNHPLMVNHODVWQRVWLPDWHULDORY]D
NRQWDNWQHOHþH ,62
Ophthalmic optics - Contact lenses - Part 4: Physicochemical properties of contact lens
materials (ISO 18369-4:2017)
Augenoptik - Kontaktlinsen - Teil 4: Physikalisch-chemische Eigenschaften von
Kontaktlinsenmaterialien (ISO 18369-4:2017)
Optique ophtalmique - Lentilles de contact - Partie 4: Propriétés physicochimiques des
matériaux des lentilles de contact (ISO 18369-4:2017)
Ta slovenski standard je istoveten z: EN ISO 18369-4:2017
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
SIST EN ISO 18369-4:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 18369-4:2017
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SIST EN ISO 18369-4:2017
EN ISO 18369-4
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2017
EUROPÄISCHE NORM
ICS 11.040.70 Supersedes EN ISO 18369-4:2006
English Version
Ophthalmic optics - Contact lenses - Part 4:
Physicochemical properties of contact lens materials (ISO
18369-4:2017)
Optique ophtalmique - Lentilles de contact - Partie 4: Augenoptik - Kontaktlinsen - Teil 4: Physikalisch-
Propriétés physicochimiques des matériaux des chemische Eigenschaften von
lentilles de contact (ISO 18369-4:2017) Kontaktlinsenmaterialien (ISO 18369-4:2017)
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 18369-4:2017 E
worldwide for CEN national Members.
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SIST EN ISO 18369-4:2017
EN ISO 18369-4:2017 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 18369-4:2017
EN ISO 18369-4:2017 (E)
European foreword
This document (EN ISO 18369-4:2017) 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 18369-4:2017.
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 18369-4:2017 has been approved by CEN as EN ISO 18369-4:2017 without any
modification.
3
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SIST EN ISO 18369-4:2017
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SIST EN ISO 18369-4:2017
INTERNATIONAL ISO
STANDARD 18369-4
Second edition
2017-08
Ophthalmic optics — Contact lenses —
Part 4:
Physicochemical properties of contact
lens materials
Optique ophtalmique — Lentilles de contact —
Partie 4: Propriétés physicochimiques des matériaux des lentilles
de contact
Reference number
ISO 18369-4:2017(E)
©
ISO 2017
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(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
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Tel. +41 22 749 01 11
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copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Physicochemical properties of contact lenses . 1
4.1 Repeatability, test methods and units of measure . 1
4.2 Extractables . 2
4.2.1 General. 2
4.2.2 Principle . 2
4.2.3 Apparatus . 2
4.2.4 Reagents . 3
4.2.5 Test samples. 4
4.2.6 Test procedure . 4
4.2.7 Calculation of results . 5
4.2.8 Test report . 5
4.3 Rigid lens flexural deformation and rupture . 5
4.3.1 Principle . 5
4.3.2 Sampling. 5
4.3.3 Preparation of samples . 6
4.3.4 Apparatus . 6
4.3.5 Procedure . 8
4.3.6 Test result . . 8
4.4 Oxygen permeability . 9
4.4.1 General. 9
4.4.2 Common elements of the methods . 9
4.4.3 Polarographic method . .10
4.4.4 Normalization of the corrected oxygen permeability using reference lenses .18
4.4.5 Test report .19
4.5 Refractive index .19
4.5.1 General.19
4.5.2 Abbe refractometer .19
4.5.3 Test samples.20
4.5.4 Procedure .20
4.5.5 Expression of test results .21
4.5.6 Test report .21
4.6 Water content .22
4.6.1 General.22
4.6.2 Gravimetric determination of water content/absorption by loss on drying
using an oven .22
4.6.3 Test report .24
5 Test report .24
Annex A (informative) Determination of oxygen permeability using the coulometric method .25
Annex B (informative) Determination of water content by refractive index .32
Annex C (informative) Calculation of oxygen permeability of hydrogel lenses based on
water content .33
Annex D (informative) Measurement of refractive index using a prism coupling device .34
Bibliography .36
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(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 18369-4:2006), 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 18369-4:2017
INTERNATIONAL STANDARD ISO 18369-4:2017(E)
Ophthalmic optics — Contact lenses —
Part 4:
Physicochemical properties of contact lens materials
1 Scope
This document specifies the methods of testing the physicochemical properties of contact lens
materials. These are extraction, rigid lens flexure and breakage, oxygen permeability, refractive index
and water content.
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 18369-1:2017, Ophthalmic optics — Contact lenses — Part 1: Vocabulary, classification system and
recommendations for labelling specifications
ISO 18369-3:2017, Ophthalmic optics — Contact lenses — Part 3: Measurement methods
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 Physicochemical properties of contact lenses
4.1 Repeatability, test methods and units of measure
The physicochemical properties or conditions listed in Table 1 are measurable characteristics of hydrogel
and non-hydrogel materials that have been used to produce commercially available contact lenses.
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(E)
Table 1 — Physicochemical properties: Test methods and units of measure
Property Units of Test method Repeatability
b
Extractables mass % 4.2
b
Flexural deformation g 4.3
a
Oxygen permeability Dk units 4.4 10 %
Refractive index dimensionless 4.5 0,01
Water content weight % 4.6 2 % absolute
a −11 2
Dk is reported in units of 10 (cm /s) ml O /(ml × mmHg) and called “Dk units” or barrer.
2
b
Repeatability of these test results shall be established in individual laboratories according to ISO 18369-1:2017,
3.1.12.8, 3.1.12.9, 3.1.12.9.1, 3.1.12.9.2 and 3.1.12.9.3.
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.
In developing new test methods, these should be capable of measuring the various parameters with a
precision (R&R) of ≤30 % of the allowed tolerance. Resolution greater than 10 % of the tolerance can
be used but will affect determination of accuracy, precision, process capability and gauge capability.
The number of independent measurements should be chosen for each method to ensure appropriate
precision and accuracy.
4.2 Extractables
4.2.1 General
Soxhlet extraction with different solvents is a standard method for quantitative determination of
substances extractable from contact lenses. The contact lenses are dried to constant mass and the
difference between the original dry mass of the lenses and the extracted dry mass determines the
quantity of extractable substances (extractables).
Knowledge of the quantity and identity of extractable substances is helpful in evaluating new
contact lens materials and in determining the subsequent pre-clinical examination programme.
The material extracted from the contact lenses may be examined by appropriate chromatographic,
spectrophotometric and wet analytical methods to identify residual monomers, cross-linking agents,
catalysts, etc. that were employed in the polymerization process.
4.2.2 Principle
This method uses a normal Soxhlet extraction apparatus. Water and at least one suitable organic
solvent are used for extraction. In selecting the organic solvent(s) to be used, consideration should be
given to the effect of the solvent upon the matrix of the material. Ideally, a solvent should not swell or
degrade the contact lens material. However, in the development of new contact lens materials, a solvent
that causes reversible swelling may give valuable information relating to the possibility for extraction
over extended periods of time. Choice of a solvent that degrades the polymer network during extraction
is not recommended, as it will remove both uncrosslinked and crosslinked material, resulting in
inaccurate measurement of extractables.
4.2.3 Apparatus
4.2.3.1 Standard borosilicate glass Soxhlet extraction apparatus (see Figure 1), consisting of
the Soxhlet extractor (30 ml suggested), condenser, round bottom flask (100 ml suggested) and a
heating mantle.
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(E)
4.2.3.2 Perforated stainless steel, sintered glass, paper or equivalent extraction thimble fitted
with a glass wool plug or other suitable closure.
4.2.3.3 Vacuum oven or equivalent drying apparatus and an analytical balance capable of
weighing to 0,1 mg.
Figure 1 — Extraction apparatus
4.2.4 Reagents
4.2.4.1 Distilled or deionized water complying with ISO 3696:1987, Grade 3.
4.2.4.2 Appropriate organic solvent (see Table 2) of analytical grade or better.
4.2.4.3 Laboratory-grade boiling stones or anti-bumping granules, along with a suitable active
desiccant. Selection of the desiccant will depend upon the characteristics of the test material.
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(E)
Table 2 — Guide to the selection of solvents for use in extraction of contact lenses
Material Suggested solvents Corresponds to
Water (distilled or deionized) Mild extraction (simulates in-eye extraction)
n-Hexane, Mild extraction (non-polar solvent)
Hydrogels (including
or
silicone hydrogels)
Organic alcohol (e.g. ethanol, iso- Extraction of majority of uncrosslinked material
propanol or methanol) (but swells and may degrade material)
Water (distilled or deionized) Mild extraction (simulates in-eye extraction)
n-Hexane, Mild extraction (non-polar solvent)
Rigid gas permeable
or
and silicone elastomers
Dichloromethane or chloroform Extraction of all uncrosslinked material
(but swells and is likely to degrade material)
4.2.5 Test samples
Test samples shall be representative of the finished product and shall be in finished contact lens form.
The method of preparing and finishing the lenses shall reflect, as far as possible, the normal production
processes including sterilization. A sufficient number of lenses shall be used so that the total dry mass
before extraction shall be no less than 200 mg.
Hydrophilic lenses are usually packaged in a solution containing inorganic salts. When using water as
the extracting solution, an adjustment in the calculation should be made for the contribution of the
inorganic salt of the packaging solution. The water content of the lenses will be required in order to
accurately calculate the contribution of the inorganic salt to the extractables. Alternatively, the lenses
may be equilibrated in at least two changes of water each for 24 h at room temperature prior to
beginning the test.
4.2.6 Test procedure
Dry the lenses, preferably under vacuum, at 60 °C ± 5 °C or other appropriate temperature to
constant mass.
NOTE 1 Drying to constant mass is achieved when two consecutive weighings between drying do not differ by
more than 0,5 mg per gram of lens weight.
Allow the lenses to cool to room temperature under vacuum or in a closed container over active desiccant
before weighing. Then, weigh the dry lenses to ±0,1 mg (m ). Next, place the lenses into the extraction
1
thimble, place boiling stones in the flask, if necessary, and fill the flask to approximately 70 % of its
capacity with the appropriate solvent (see Table 2). Place the round-bottom flask in the heating mantle.
Place the extraction thimble into the Soxhlet apparatus. Then, attach the Soxhlet apparatus to the flask.
Place a condenser on top of the extraction apparatus. When using a volatile or flammable solvent, the
extraction apparatus should be placed in a fume hood.
Turn on heat and water and extract the lenses for at least 4 h. Allow the solvent to cool to room
temperature before removing the lenses from the extraction thimble. Dry the lenses to constant mass
as described above and weigh to the nearest 0,1 mg (m ). Calculate results as per Formula (1).
2
NOTE 2 If the dried lenses are fragile and fragmentation may have occurred leading to inaccuracies in
measurement, the extraction solvent can be quantitatively dried down to constant mass and the resultant
extractables residue weighed to the nearest 0,1 mg (m ). In this case, calculate results as per Formula (2).
3
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(E)
4.2.7 Calculation of results
The quantity of extracted material shall be expressed as a mass fraction (m ) in percent of the
extracted
initial dry mass as shown in Formula (1):
mm−
()
12
% extracted= ×100 (1)
m
1
where
m is the mass of lenses prior to extraction;
1
m is the mass of extracted lenses.
2
Alternatively, the extraction solvent can be quantitatively dried down to constant mass and the
resultant extractables residue weighed to the nearest 0,1 mg (m ) and used to calculate the quantity of
3
extracted material as shown in Formula (2):
m
3
% extracted= ×100 (2)
m
1
4.2.8 Test report
The test report for extractables shall conform to that in Clause 5 and contain the following information
for hydrophilic material:
a) the composition of the initial hydrating solution;
b) a statement as to whether the percentage of extractable substances has been adjusted for the salt
content of the hydrating solution;
c) if the contact lenses were equilibrated in water before the beginning of the test;
d) the method used to calculate quantity of extracted material, e.g. whether Formula (1) or Formula (2)
was used for the calculation.
4.3 Rigid lens flexural deformation and rupture
4.3.1 Principle
The test, which is a destructive test, applies an increasing load at the edge of a rigid lens across the
total diameter until, ultimately, the test sample fractures. The test is carried out in an apparatus which
allows the load and flexural deformation to be monitored continuously. Both the flexural deformation
strength and flexural deformation at rupture are determined, as well as flexural deformation strength
at 30 % deformation. The latter is derived from the flexural load-deformation curve. Either normal
production or specially constructed rigid contact lenses can be tested.
It should be noted that variability in the test results may also result from inconsistencies in lens
manufacturing method and may not necessarily be indicative of the material itself.
4.3.2 Sampling
4.3.2.1 General samples
In order to demonstrate the degree of resistance to breakage by the material, general samples for
testing shall be normal, commercially available rigid, single vision contact lenses and shall not have
been specially treated or adjusted.
Contact lenses which have toroidal zones or truncations shall not be used.
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SIST EN ISO 18369-4:2017
ISO 18369-4:2017(E)
The specified label back vertex power (F′ ) shall be the same for all samples and shall be between
L
+0,50 D and −0,50 D.
The specified back optic zone radius (r ), or radius of the vertex sphere, shall be the same for all samples
0
and shall be between 7,75 mm and 7,85 mm.
4.3.2.2 Samples for material comparison
When special samples are prepared in order to compare materials, the contact lenses shall have the
following specifications:
— front surface: single cut, radius of curvature 8,000 mm ± 0,025 mm;
— back surface: single cut, radius of curvature 7,800 mm ± 0,025 mm;
— total diameter: 9,5 mm ± 0,1 mm;
— centre thickness: 0,20 mm ± 0,01 mm;
— edge thickness: 0,24 mm ± 0,01 mm;
— edge form: rounded;
— maximum prismatic error: 0,5 cm/m.
The method of manufacture shall be stated in the test report.
4.3.2.3 Quantity
Three contact lenses from each of three different materi
...
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