ISO 9342-2:2005

INTERNATIONAL ISO
STANDARD 9342-2
First edition
2005-11-15
Optics and optical instruments — Test
lenses for calibration of focimeters —
Part 2:
Test lenses for focimeters used for
measuring contact lenses
Optique et instruments optiques — Verres étalons pour l'étalonnage
des frontofocomètres —
Partie 2: Verres étalons pour frontofocomètres pour le mesurage des
lentilles de contact
Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Foreword
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(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
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ISO 9342-2 was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 7,
Ophthalmic optics and instruments.
ISO 9342 consists of the following parts, under the general title Optics and optical instruments — Test lenses
for calibration of focimeters:
⎯ Part 1: Test lenses for focimeters used for measuring spectacle lenses
⎯ Part 2: Test lenses for focimeters used for measuring contact lenses
INTERNATIONAL STANDARD ISO 9342-2:2005(E)

Optics and optical instruments — Test lenses for calibration of
focimeters —
Part 2:
Test lenses for focimeters used for measuring contact lenses
1 Scope
This part of ISO 9342 specifies requirements for test lenses for focimeters that are used to measure contact
lenses. These test lenses are used to find the precise correction values that are needed to convert the power
values measured to back vertex power values, as defined in Clause 3.
This part of ISO 9342 applies to focimeters meeting the requirements of ISO 8598.
2 Normative references
The following referenced documents are indispensable for the application 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 7944:1998, Optics and optical instruments — Reference wavelengths
ISO 8598:1996, Optics and optical instruments — Focimeters
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1
back vertex power
F
bv
reciprocal of the paraxial value of the back vertex focal length, measured in metres
−1
NOTE 1 The unit for expressing vertex power is the reciprocal metre (m ). The name for this unit is “dioptre”, and the
symbol is D.
NOTE 2 Conventionally, the back vertex power is specified as the “power“ of a contact lens.
3.2
spherical test lenses
test lenses having spherical front and back surfaces so that their back vertex power may be expressed by a
single value
3.3
reference wavelength
wavelengths specified in ISO 7944
NOTE For the purpose of this part of ISO 9342, the reference wavelength can be either the green mercury line
(λ = 546,07 nm) or the yellow helium line (λ = 587,56 nm).
e d
4 Design requirements and recommendations for test lenses
4.1 General
Test lenses should be made of homogeneous white crown glass selected to be free of bubbles and striae in
an area of 4 mm radius surrounding the centre of the free aperture.
It is accepted that other materials can also be used provided their use result in lenses with a durability and
optical reproducibility within the given tolerance over time and that can be manufactured to the same standard
of uncertainty and form, as the glass lenses specified above.
Test lenses should have a protective mount that is designed so that, when the lens is correctly placed on the
lens support, the focimeter is not obstructed.
4.2 Spherical test lens
For a complete set of spherical test lenses, the following set of nominal back vertex powers is recommended:
− 20 D, − 15 D, − 10 D, − 5 D, + 5 D, + 10 D, + 15 D, + 20 D.
Spherical test lenses should have a free aperture of at least 8 mm.
The curvature of the back surface shall approximately correspond to those of common contact lenses, which
are in the range 7 mm to 9 mm, so that the spherical aberration of the test lenses approximates that exhibited
by common contact lenses.
The nominal curvature of the back surface is recommended as 8 mm, a value meeting the requirement of
ISO 18369-3, which is approximately equal to the front surface radius of cornea for the human eye. The radius
tolerance for back surface curvature is ± 0,1 mm.
The centre thickness for a given back vertex power shall be chosen to be in the range given in Table 1.
These centre thickness value ranges are required to guarantee the durability of the test lenses during use. It is
for this reason that they are generally greater than those for common contact lenses.
Table 1 — Design range for the standard test lenses
Nominal back vertex power, F
Range for centre thickness
bv
−1
(mm)
(m )
− 20 0,5 to 1,5
− 15 0,5 to 1,5
0,5 to 1,5
− 10
− 5 0, 5 to 1,5
+ 5 1 to 2
+ 10 1 to 2
+ 15 1 to 2
1 to 2
+ 20
2 © ISO 2005 – All rights reserved

5 Tolerances for spherical test lenses
The design value of each lens shall be stated along with the reference wavelength used to determine this
−1
value. The permissible tolerances for all spherical test lenses shall be within ± 0,03 m of their stated values.
NOTE In Annex A, an example is given for the proper design of test lenses that meets this requirement and the
requirement of Table 1.
Annex A
(informative)
Manufacture of test lenses for calibration of focimeters
used for measuring contact lenses
A.1 General
Spherical test lenses, which meet the tolerances given in 4.2 and Clause 5, can be manufactured by
observing the specifications and procedure described in A.2 to A.8.
To manufacture test lenses in accordance with this annex, the manufacturer will need a selection of master
test surfaces against which the test lens surfaces can be checked, using standard precision optica
...