EN ISO 12864:1997

SLOVENSKI STANDARD
01-januar-2000
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Ophthalmic optics - Contact lenses - Determination of scattered light (ISO 12864:1997)
Augenoptik - Kontaktlinsen - Bestimmung des Streulichtes (ISO 12864:1997)
Optique ophtalmique - Lentilles de contact - Détermination de la lumiere diffusée (ISO
12864:1997)
Ta slovenski standard je istoveten z: EN ISO 12864:1997
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 12864
First edition
1997-12-15
Ophthalmic optics — Contact lenses —
Determination of scattered light
Optique ophtalmique — Lentilles de contact — Détermination de la lumière
diffusée
A
Reference number
ISO 12864:1997(E)
ISO 12864:1997(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.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 12864 was prepared by ISO/TC 172 Optics and optical instruments, Subcommittee SC 7
Ophthalmic optics and instruments.
©  ISO 1997
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
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Internet central@iso.ch
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Printed in Switzerland
ii
© ISO
ISO 12864:1997(E)
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
radiation 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 small-angle scattering of contact lenses (see
figure 1).
1CL
2 Optical axis
3 Scattered light
Figure 1 — Small-angle scattering of a contact lens
iii
INTERNATIONAL STANDARD  © ISO ISO 12864:1997(E)
Ophthalmic optics — Contact lenses — Determination of scattered
light
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 reference 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
International 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. Members 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 purposes of this International Standard, the definitions given in ISO 8320 apply, together with the following.
3.1 luminance factor, l

Ratio of the luminance of the surface element in the given direction (the scattered light, L ) to that of a perfect
s
reflecting or transmitting diffuser identically illuminated (here taken to be the illuminance, ).
E
NOTE The luminance factor is expressed using equation (1):
L cd / m
s
l = in
(1)
E lx
*
3.2 reduced luminance factor, l
Ratio of the
...