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Technical
Report
ISO/TR 11826
First edition
Ophthalmic optics — Spectacle
2024-07
lenses — Aspects of three-
dimensional properties and
reference markings
Optique ophtalmique — Verres de lunettes — Aspects des
propriétés tridimensionnelles et marquages de référence
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Technical background. 1
4.1 General .1
4.2 Spectacle lenses .1
4.3 Spectacle frames .2
5 Influence of three-dimensional effects and necessity to deal with them . 3
5.1 Optical effects . . .3
5.2 Reference points on front surface versus back surface meeting the eye in as-worn
position .7
5.3 Positioning errors from the images of markings on the back surface .10
5.3.1 General .10
5.3.2 Simulation results . 12
6 Different approaches to specifying measurement positions and alignment .15
6.1 General . 15
6.2 Reference coordinate systems defined by engravings .16
6.2.1 General .16
6.2.2 Reference coordinate system for front side engravings .16
6.2.3 Reference coordinate system for back side engravings .17
6.2.4 Data Communication Standard (DCS) from the Vision Council .19
6.3 Summary .21
7 Conclusion .22
Bibliography .24
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 7,
Ophthalmic optics and instruments.
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iv
Introduction
In current standards, spectacle lenses are mostly treated as two-dimensional objects.
However, knowing their three-dimensional geometrical properties is helpful to fully understand their
optical effects. Therefore, these are already taken into account in the industry in some instances, e.g. to
increase the performance of products and the accuracy of measurements.
The aim of this document is to deliver background information on this topic, to provide helpful terminology
including parameters, and to present some ways of dealing with their impacts. It is intended as a source of
information to the manufacturers of spectacle lenses, measurement systems, and mounting equipment as
well as to the optometric and dispensing professions.
v
Technical Report ISO/TR 11826:2024(en)
Ophthalmic optics — Spectacle lenses — Aspects of three-
dimensional properties and reference markings
1 Scope
This document is applicable to the three-dimensional aspects of spectacle lenses and their mounting in
frames. It gives possible details of how these aspects can be taken into account, particularly for lenses with
their permanent reference engravings (markings) on their back surface.
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 13666, Ophthalmic optics — Spectacle lenses — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13666 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 Technical background
4.1 General
Changes in the method of manufacture of spectacle lenses and in the styling of some spectacle frames have
th
generated problems of positioning lenses correctly in the frame that did not occur in the 20 century.
Conversely, free form manufacture allows the benefits of individualized computer enhancement and more
sophisticated lens designs but requires an improved, and available, ability to position lenses.
[1]
Many aspects related to the use of free form technology are explained in ISO/TR 18476 , which also covers
optical effects relevant to the topics discussed in this document.
4.2 Spectacle lenses
The reference points and design reference points are specified in ISO 13666 to be on the front surface of the
lens. This is logical, in that the marking device on focimeters dots the front surface of the lens, in particular
the optical centre for single-vision lenses. This dot is used for positioning the uncut lens correctly for edging it
to shape for mounting in the frame. Although errors in prism imbalance (relative prism error) are generated
if lenses are not correctly centred in the frame in front of the eyes, there is no or little effect on the binocular
field of view for single-vision lenses or for the far and near fields of view with multifocal lenses. Position-
specific single-vision lenses and power-variation lenses have, however, to be positioned so that their optical
properties including, where applicable, the (intermediate) corridor and near portion are aligned with the
eyes. The conventional construction of progressive-power and degressive-power lenses was to use a blank
with the power-variation surface moulded (or sagged for glass blanks) on the front surface of the blank, then
surfacing the prescription onto the back surface. The two permanent alignment reference markings were
positioned on the complicated surface, and thus automatically on the front, and were used to generate the
reference point for mounting the lenses.
The ability to combine the prescription and complicated surface of power-variation lenses on the back
[1]
surface and generate this using free form technology – see ISO/TR 18476 – means that the permanent
alignment reference markings are now usually positioned on the back surface of the lens. These markings
are, however, viewed through the front surface when positioning the uncut lens for mounting in the frame.
Prism incorporated in the lens, whether prism thinning or prism required by the lens order, displaces the
apparent position of these markings and hence the midpoint between them, while the convex front surface
will magnify their separation. Position-specific single-vision lenses also have complicated back surfaces
generated with free form technology, and are likely therefore also to be marked on the back surface.
In many respects, it is more logical to have the reference points on the back surface of the lens, since it is rays
leaving the back surface that enter the eye, but this change requires an enormous change to the methods of
working in the lens mounting industry, including non-permanent lens inking and edging block positioning
presently on the front. Moreover, nose pads and spectacle sides are likely to be in the way when measuring
the positioning of mounted lenses. Changing to using the back surface for reference points for lenses is
therefore a “non-starter”.
4.3 Spectacle frames
Until the early 2000's, spectacle frames had fronts which were relatively flat so that the two lenses lay in
the same plane, or nearly so. Since then, a minority of frames have been designed with a significant face
[2]
form or wrap angle (see ISO 8624 ). This can have an effect on the decentration needed – the geometrical
relationship between various distances is given in the notes to entry for the term “centration point” in
ISO 13666.
Key
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