BS EN ISO 8980-2:1997 download.Ophthalmic optics Uncut finished spectacle lenses Part 2: Specifications for progressive power lenses.
1 Scope
This part of Iso 8980 specifies requirements for the optical and geometrical properties for uncut finished progressive spectacle lenses.
2 Normative references
The following standards contain provisions which, through reference in the text, constitute provisions of this part of ISO 8980. At the time of publication. the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO 8980 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of lEG and ISO maintain registers of currently valid International Standards.
ISO 7944:1984, Optics and optical instruments — Reference wavelengths.
ISO 8598:—, Optics and optical instruments — Focimeters’.
ISO 8980-1:1996, Ophthalmic optics — Uncut finished spectacle lenses — Part 1: Specifications for single-vision and niultifocal lenses.
ISO 1:3666:—, Ophthalmic optics — Spectacles lenses — Vocabulary’.
3 Definitions
For the purposes of this part of ISO 8980. the definitions given in ISO 13666 apply.
4 Classification
Finished lenses are classified as follows:
a) single-vision finished lenses;
b) multifocal finished lenses:
c) progressive power finished lenses.
5 Requirements
The tolerances shall apply at a temperature of 23 °C ± 5 °C.
5.1 Optical requirements
5.1.1 General
The optical tolerances shall apply at the reference points of the lens at one of the reference wavelengths specified in Iso 7944.
The as-worn position can result in the apparent power to the eye being different from that determined as a result of the focimeter measurement.
If the manufacturer has applied corrections to compensate for the as-worn position, then the tolerances shall apply to the corrected value and this corrected value shall be stated by the manufacturer on the package or in an accompanying document (see 8.1).
The measured addition power is principally influenced by the prescribed surface. In particular cases, e.g. oblique cylinders or high minus powers, the deviation of the measured addition power of finished progressive lenses can exceed the above mentioned tolerances. The manufacturer shall submit corrected values on request (see 8.2).
5.1.2 Tolerances on the power of progressive power lenses for the distance portion (back vertex power)
The optical power shall be determined using a focimeter complying with ISO 8598 or an equivalent method.
5.1.2.1 Tolerances on the power of the lenses Spherical, aspherical and cylindrical power lenses shall comply with the tolerances on each meridian, A, and with the tolerances on the cylinder, B (see Table 1).
5.1.2.2 Tolerances on the direction of cylinder axis The tolerances on the direction of cylinder axis as specified in Table 2 shall be measured using the method described in 6.2.
6.2 Addition power measurement method Place the lens so that the progressive surface is against the focimeter lens support and centralize the lens at the near reference point.
Using a focusing focimeter, measure the near vertex power after focusing the more nearly vertical lines of the target.
Then measure the distance vertex power at the distance reference point, with the progressive surface against the focimeter lens support, by focusing the lines of the target which are closest to the vertical.
Calculate the addition power as the difference between the near vertex power and the distance vertex power.
Lenses for which the addition power has been determined by the measurement method given in Iso 8980-1:1995, 6.22), are not excluded from this part of ISO 8980 for a transition period of 5 years after publication of this edition.
Alternative measurement methods are acceptable if shown to perform equivalently to the above reference method.
In the case of special conception design, if the reference method is not applicable, the manufacturer should specify the reference points for the addition measurement
In the case of negative lenses with negative distance powers of 6,00 D or more, back vertex power measurement methods are permitted. If the lens is designed according to the back vertex power measuring method, this should be stated by the manufacturer.
If the manufacturer publishes information on the evaluation of a progressive addition lens, then the method of determination of those characteristics should be based on the method described in Annex B.
6.3 Material and surface quality See Annex A.
7 Marking
7.1 Permanent marking
The lens shall be permanently marked at least with the following.
a) The alignment reference markings comprising two marks located 34 mm apart, equidistant to a vertical plane through the fitting point or prism reference point.
b) Indication of the addition power, in dioptres.
c) Indication of the manufacturer, or supplier, or tradename, or trademark.
Lenses, on which the reference marking is not located in accordance with a) and lenses which are not inscribed with the tradename or manufacturer’s name are not excluded from the part of ISO 8980 for a transition period of 5 years after publication of this edition.
7.2 Optional non-permanent marking
The following optional non-permanent marking is recommended:
a) the alignment reference marking;
b) indication of the distance reference point;
c) indication of the near reference point;
d) indication of the fitting point;
e) indication of the prism reference point.
8 Identification
8.1 Identification of the lens to be stated on the package of the lens of in an accompanying document
The following information shall be stated:
a) dioptric power, in dioptres;
b) nominal lens size, in millimetres;
c) colour (if not white);
d) identification of any coating;
8.2 Information to be made available The following information shall be available on request:
a) centre or edge thickness, in millimetres; b) base curve, in dioptres:
c) optical properties (including constringence and spectral transmittance);
d) prism thinning (if applicable);
e) centration chart for the reconstruction of the non-permanent markings relative to the permanent markings.
9 Reference to this part of ISO 8980
If the manufacturer or supplier claims compliance with this part of ISO 8980, reference shall be made to ISO 8980-2 either on the package or in available literature.