1、BRITISH STANDARD BS EN ISO 12864:1998 Ophthalmic optics Contact lenses Determination of scattered light The European Standard EN ISO 12864:1997 has the status of a British Standard ICS 11.040.70BSENISO12864:1998 This British Standard, having been prepared under the directionof the Health and Environ
2、ment Sector Board, waspublished under the authorityof the Standards Boardand comes into effect on 15 September 1998 BSI 05-1999 ISBN 0 580 302265 2 National foreword This British Standard is the English language version of EN ISO 12864:1997. It is identical with ISO 12864:1997. The UK participation
3、in its preparation was entrusted by Technical Committee CH/78, Ophthalmic optics, to Subcommittee CH/78/4, Physical properties of contact lenses, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the in
4、terpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references Attention is drawn
5、to the fact that CEN and CENELEC Standards normally include an annex which lists normative references to international publications with their corresponding European publications. The British Standards which implement international or European publications referred to in this document may be found i
6、n the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. Textual error The textual error set out below was identified when the English language version of ENISO12864:1997 was ad
7、opted as the national standard. It has been reported to CEN in a proposal to amend the text of the European Standard. In 3.1, line 1, the text should be enclosed by parentheses ( ). A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards
8、are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theEN ISO title page, page 2, the ISO title page, pages ii to iv
9、, pages 1 to 4, aninside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBSENISO12864:1998 BSI
10、 05-1999 i Contents Page National Foreword Inside front cover Foreword 2 Foreword iii Text of ISO 12864 1ii blankEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 12864 December 1997 ICS 11.040.70 Descriptors: See ISO document English version Ophthalmic optics Contact lenses Determination of
11、scattered light (ISO 12864:1997) Optique ophtalmique Lentilles de contact Dtermination de la lumire diffuse (ISO12864:1997) Augenoptik Kontaktlinsen Bestimmungdes Streulichts (ISO12864:1997) This European Standard was approved by CEN on30 November1997. CEN members are bound to comply with the CEN/CE
12、NELEC 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 Central Secretariat or to any
13、 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 Central Secretariat has the same status as the official versions. CE
14、N members are the national standards bodies of Austria, Belgium, CzechRepublic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de No
15、rmalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1997 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref.No.ENISO12864:1997EENISO12864:1997 BSI 05-1999 2 Foreword The text of the Internationa
16、l Standard ISO12864:1997 has been prepared by Technical Committee ISO/TC172 “Optics and optical instruments” in collaboration with Technical Committee CEN/TC170 “Ophthalmic optics”, the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, eith
17、er by publication of an identical text or by endorsement, at the latest by June1998, and conflicting national standards shall be withdrawn at the latest by June1998. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implem
18、ent this European Standard: Austria, Belgium, CzechRepublic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of the International Standard ISO12864:1997 was a
19、pproved by CEN as a European Standard without any modification. NOTEA-deviations are given in Annex ZA (informative).ENISO12864:1997 ii BSI05-1999 Contents Page Foreword iii Introduction 1 1 Scope 2 2 Normative references 2 3 Definitions 2 4 Principle 2 5 Apparatus 2 6 Procedure 2 7 Test report 4 An
20、nex ZA (informative) A-deviations Inside back cover Figure 1 Small angle scattering of a contact lens 1 Figure 2 Arrangement of apparatus for measurement of scattered light 3ENISO12864:1997 BSI 05-1999 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of
21、 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. Int
22、ernational 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. Draft International Standards adopted by the technical co
23、mmittees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least75% of the member bodies casting a vote. International Standard ISO12864 was prepared by ISO/TC172 Optics and optical instruments, Subcommittee SC7 Ophthalmic optics and ins
24、truments.iv blankENISO12864:1997 BSI 05-1999 1 Introduction If light is scattered significantly when passing through a contact lens (CL), contrast is reduced and the visual performance of the wearer is impaired. In this case, the light which is scattered at a large angle to the direction of radiatio
25、n is generally less disturbing than light which is scattered at small angles. In particular, light scattered at small angles may cause problems for drivers when the sun is low in the sky, when it reflects off wet roads and at night with oncoming traffic. Therefore it is desirable to minimize the sma
26、ll-angle scattering of contact lenses (seeFigure 1). Figure 1 Small-angle scattering of a contact lensENISO12864:1997 2 BSI 05-1999 1 Scope This International Standard describes a method for the determination of the scattering of light by contact lenses. The test method described is given as a refer
27、ence method. The existence of this International Standard does not imply in any way that the testing of contact lenses for light scatter is a requirement. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this Internatio
28、nal Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Memb
29、ers of IEC and ISO maintain registers of currently valid International Standards. ISO 8320:1986, Optics and optical instruments Contact lenses Vocabulary and symbols. ISO 10344:1996, Optics and optical instruments Contact lenses Saline solution for contact lens testing. 3 Definitions For the purpose
30、s of this International Standard, the definitions given in ISO8320 apply, together with the following. 3.1 luminance factor, lRatio of the luminance of the surface element in the given direction (the scattered light, L s ) to that of a perfect reflecting or transmitting diffuser identically illumina
31、ted (here taken to be the illuminance, E). NOTEThe luminance factor is expressed using equation (1): 3.2 reduced luminance factor, l * Ratio of the luminance factor, l, to the transmittance, . NOTEThe reduced luminance factor, which is the luminance factor expressed so as not to depend on the transm
32、ittance of the contact lens, is obtained using equation (2): 4 Principle The beam from a He-Ne laser is diverged (using the two lenses L 1and L 2 ) onto the centre of the contact lens. The beam is deflected according to any inherent prismatic effect at this point. A cone of scattered light is formed
33、 around the deflected beam. The sensor S is conjugate with the centre of the lens. S, L 3and D 1 /D 2lie along the deflected beam. Apertures D 1 , D 2are subsequently used to assess the scattered light of the cuvette with and without the contact lens. 5 Apparatus The test arrangement is shown inFigu
34、re 2. Using two lenses L 1and L 2 , the beam from a He-Ne laser is extended onto the centre of the contact lens, these two lenses constituting an afocal system. The contact lens is mounted so that it can be rotated around the optical axis of the laser beam and so that the centre of the contact lens
35、lies on the axis of rotation. The part of the test assembly consisting of the diaphragms D 1or D 2 , the lens L 3and the sensor S is constructed so that it can pivot. The axis of pivoting passes through the centre of the contact lens. This ensures that, whatever the prismatic effect of the contact l
36、ens at the point of measurement, the deflected central beam always runs parallel to the optical axis of the assembly, within the pivoting range. Since the contact lens itself is mounted so that it can be rotated around the optical axis, the prismatic deflection can always be arranged so that it lies
37、 within the plane of the pivoting movement. NOTEThe capacity to rotate the contact lens and to pivot the sensor arm is generally not necessary for testing a contact lens of nominal plano power. 6 Procedure 6.1 Calibration of the apparatus Set up the apparatus, the essential features of which are sho
38、wn inFigure 2, with the cuvette filled with saline solution conforming to ISO10344 but with the contact lens absent. Arrange the sensor S, lens L 3and the diaphragm D 1so that they all move in the same plane and are positioned to record the maximum intensity (that is, all lie on the axis of the lase
39、r beam). Measure the flux 9 1CUfalling onto the sensor S, corresponding to the light passing directly through the cuvette filled with saline solution. Replace the circular diaphragm D 1by the annular diaphragm D 2 . Measure the flux 9 2CUfalling onto the sensor S, corresponding to the scattered tran
40、smitted light. Calculate , the solid angle defined by the annular diaphragm. (1) (2) l Ls E - in cd m2 lx - = l * l E - Ls E .E - in cd m2 lx - = =ENISO12864:1997 BSI 05-1999 3 Obtain the reduced luminance factor for theapparatus and the cuvette filled with saline solution for the solid angle using
41、equation (3): (3) l*CU NOTE 1The vertex powers of the lenses are only given as indications. They can be selected differently, if for instance greater beam spread is desired or a reduced image of the test piece is to be shown on the radiation sensor. NOTE 2A class 2 laser (see IEC60825-1 a ) with a b
42、eam diameter between0,6 mm and1 mm is recommended. a IEC60825-1:1993, Safety of laser products Part1: Equipment classification, requirements and users guide. Figure 2 Arrangement of apparatus for measurement of scattered lightENISO12864:1997 4 BSI 05-1999 6.2 Testing a contact lens Fill the cuvette
43、with saline solution conforming to ISO10344 and mount the contact lens under test in the cuvette. Rotate the cuvette with the contact lens so that the deflected beam is in a known plane. Arrange the sensor S, lens L 3and the diaphragm D 1so that they all move in the same plane and are positioned to
44、record the maximum intensity (that is, all lie on the axis of the deflected beams). Measure the flux 9 1CLfalling onto the sensor S, corresponding to the light passing directly through the contact lens in the cuvette filled with saline solution. Replace the circular diaphragm D 1by the annular diaph
45、ragm D 2 . Measure the flux 9 2CLfalling onto the sensor S, corresponding to the scattered transmitted light for the solid angle defined by the annular diaphragm. Obtain the reduced luminance factor for the apparatus and the contact lens in the cuvette filled with saline solution for the solid angle
46、 using equation (4): 6.3 Calculation of result Calculate the reduced luminance coefficient of the contact lens using equation (5): 7 Test report The test report shall contain at least the following information: a) a reference to this International Standard, i.e.ISO12864; b) the identification of the
47、 contact lens tested; c) the reduced luminance coefficient of the contact lens ; d) the date of examination. (4) l*tot (5) l* CLENISO12864:1997 BSI 05-1999 Annex ZA (normative) A-deviations A-deviation: National deviation due to regulations, the alteration of which is for the time being outside the
48、competence of the CEN/CENELEC member. This European Standard does not fall under any Directive of the EC. In the relevant CEN/CENELEC countries these A-deviations are valid instead of the provisions of the European Standard until they have been removed. The legislative situation in Germany requires
49、the unit “dioptre” be designated by the symbol “dpt” instead of “D”. This is to avoid conflict with the rules of ISO1000 being the basic International Standard on symbols and units and with the respective basic resolution of the CGPM (International Conference on Weights and Mesures). Identification of the regulation: Gesetz ber die Einheiten im Mewesen vom02.07.1969 in der Fassung der Bakanntmachung vom22.04.1985; and Ausfhrungsverordnung zum Gesetz
