ORLAB Technical Note

Transcription

1 ORLAB Technical Note Ophthalmic Product Series Issue 6 A series of technical notes to aid understanding of standards, reasons for failure to comply and hints on avoiding the problem. Differences between AS and ISO 21987:2011 as they relate to :2007 General AS has been replaced by a suite of ISO standards, not all of which are necessary to have to work with , since this deals with finished and mounted. ISO is the direct equivalent for the purposes of working to These standards are available from Spectacles - Spectacle (pdf $70.75 hardcopy $78.61) ISO 21987:2011 Ophthalmic optics - Mounted spectacle (pdf $95.87 hardcopy $106.52) Differences This tech note will only address the provisions of relevant to finished (Section 4) as applicable in although this refers to the provisions for finished uncut (Section 3) quite widely. The testing of plano prescription eye protectors in is for the purposes of evaluating the frame and, as such, they are tested fully according to not Accreditation number 1923 Accredited since 1985 ORLAB 2011 Page 1 of 13 AS and ISO 21987:2011

2 Page 2 of &.2 Back vertex power Back vertex power tolerance ISO has tables that include both spherical power and astigmatic power requirements. The tolerances depend on the nominal spherical power and the nominal cylindrical power. The easiest way to represent the changes is in a set of graphs. The tolerance in for the nominally plano has also been included. In a nutshell and with one exception, the provisions of ISO are the same as or less stringent. The tolerances reported here are for single vision and multifocal. Tolerances for progressive (degressive are included in ISO but did not exist at the time of the writing of ) are also included in the standards. Refer to Tables 3.1 & 3.2 od and Table 2 of ISO A table of comparisons is available. ORLAB 2011 Page 2 of 13 AS and ISO 21987:2011

3 Page 3 of &.2 Back vertex power Continued Back vertex power tolerance Continued Addition power Multifocal and progressive Surface power Addition power tolerance for multifocal and progressive These are the same in both standards. Add Tolerance 4.00 ±0.12 >4.00 ±0.18 When the surface power is specifically ordered These are general requirements and untestable in a quantitative sense. ORLAB 2011 Page 3 of 13 AS and ISO 21987:2011

4 Page 4 of 13 Material and surface quality Refers to Edge quality Mounted Monograms, logos and decorations Material and surface quality. Refers to Annex A 6.1 General Note 2 refers to Annex B Annex B.2 Recommendations on glazing ISO is much more prescriptive about how the inspection is to take place. But the Annex is informative not normative is more specific and should be given precedence (given that it is a safety standard). These are general requirements and untestable in a quantitative sense. The contains only a note (which is not part of the standard) and the Annex is informative only is more specific and should be given precedence (given that it is a safety standard). Essentially the same. AS uses should, which is advisory, and the Annex of ISI is informative. The provisions of AS echo those developed for AS1067 Sunglasses at the time. Previous editions of the standards lacked this and it could be interpreted that anything added to the lens as decoration was a defect. The was added as a permissive that says, in a nutshell, the central 30mm of the lens cannot contain such things but anywhere else on the lens it is OK. It remains to be seen how ISO is to be interpreted in this respect. ORLAB 2011 Page 4 of 13 AS and ISO 21987:2011

5 Page 5 of Cylinder axis Cylinder axis direction tolerance Optical centration and prism Single mounted Applies to single. Not applicable. ORLAB 2011 Page 5 of 13 AS and ISO 21987:2011

6 Page 6 of Optical centration and prism Lens pairs Prism imbalance (relative prism error) for pairs of single-vision and multifocal Prism imbalance (relative prism error) for progressive-power and degressive-power Note: Testing is normally carried out on prescription eye protectors with a PD of 64 (medium head) or 54mm (small head) as required in Compliance authorities may set these PDs as the prescribed PD for the purposes of samples for testing Prism base setting for mounted. Tolerances on prism are the same whether it is a limit on prism where none is prescribed and the tolerance of the prescribed prism does not exceed 2.. ISO has greater tolerances for ordered prism in progressive and degressive. See Figures 1 & 2 of ISO ISO relies on assessing the horizontal and vertical components separately. ORLAB 2011 Page 6 of 13 AS and ISO 21987:2011

7 Page 7 of Minimum lens thickness Maximum lens thickness Lens thickness Tolerances for multifocal segment location Mounting of progressive Section 5 Special requirements Appendix A Lens power measurement 5.4 Thickness tolerance Multifocal Progressive-power and degressivepower 6 Test methods requires the minimum thickness to be declared. provisions are advisory. Tolerance on ordered thickness ISO ± 0.2mm ± 0.3mm Tolerance on ordered segment height or distance below datum or segment inset ISO ± 0.5mm ± 1.0mm Tolerance on height and horizontal location of fitting cross ISO ± 0.5mm ± 1.0mm When dealing with , will apply. Especially 5.5 for use in eye protectors. AS is silent on the quality of the focimeter. ISO requires a focimeter complying with ISO ORLAB 2011 Page 7 of 13 AS and ISO 21987:2011

8 Page 8 of 13 A4.2 Addition power of multifocal lens blanks and A4.3 Progressive power lens blanks and 6.4 Addition power measurement Aperture of measurement: = 3-6mm and ISO = Not prescribed but shall not adversely affect the accuracy of measurement by introducing excessive sagittal error. Wavelength: = not set. ISO (by ISO 8598) = mercury green line (546.07nm) or helium yellow line (587.56nm). Calibration is silent. ISO requires calibration using the specified in IS The test procedure differs in the words used but is much the same in principle in the two standards. In particular, both specify difference in front vertex power as the appropriate method when the segment or progressive surface is on the front surface (a point not grasped by many people). The only exception is if the manufacturer specifies otherwise Segment tilt for straight-top and curved-top segments ±2 ORLAB 2011 Page 8 of 13 AS and ISO 21987:2011

9 Page 9 of Alignment marking tilt ±2 (progressive and degressive). Appendix C Lens flammability Appendix E Photochromics Appendix F Fatigue of photochromics Appendix G Adhesion test for surface coatings Appendix H Chemical stability test Appendix I Thermal stability test for surface coatings See ISO :2011 See ISO :2011 With , the resistance to ignition requirements may apply in some circumstances. ISO :2011 Ophthalmic optics - Uncut finished spectacle - Transmittance specifications and test methods. When dealing with , will apply. Fatigue in photochromics is a very fraught subject and th industry seems to want to avoid the issue. Results are very test method dependent. I am sure there is an ISO method somewhere. When dealing with , will apply. ORLAB 2011 Page 9 of 13 AS and ISO 21987:2011

10 Page 10 of 13 Compensated powers Where the completed spectacle has a significant amount of wrap around resulting in a high face form angle the line of sight in the primary position through the spectacle lens will not intersect the lens at normal incidence. This will give rise to oblique effects and can be compensated for by changing the les power. To measure the effective power of the lens, the direction of measurement must be the same as in normal wear. ie measured in the as-worn position. Neither AS nor ISO provide a test method by which this can be assessed but does state, in 5.2 (last para) that the tolerances apply to the actual prescription not the power of the compensated. The combination of the frame styles in the eye protection field with the need for prescription has highlighted this problem. It is not obvious how measurements on compensated should be made. It is not appropriate simply to tilt the lens on the focimeter aperture since it will pivot on one side of the rim of the aperture and the measurement point (being the centre of the aperture) will not be in the plane of the entrance aperture of the focimeter and an error will be introduced. At this stage it is an open question as to how compensated should be assessed, probably until someone submits compensated for certification. At that stage there should be a discussion between the manufacturer, the certifying authority and a test authority. The chair of Committee MS-24, which is responsible for spectacle lens standards, will probably have to be involved too. Disclaimer These notes are of a general nature, you should investigate how these standards changes apply to you and your products yourself and not rely solely on these general guidelines. Questions on use of the Standards Mark and how this might affect your current licences to use the mark, contact or Stephen Dain Brian Cheng Thao Ngo ORLAB 2011 Page 10 of 13 AS and ISO 21987:2011

11 Data tables Values that differ between standards are in red, bold and italic Table 1 Tolerances on mean sphere Higher principal meridian (dioptres) (+ or -) Mean sphere tolerance (dioptres) ISO >3.00 to >9.00 to >12.00 to > Table 2 Tolerances on meridional values power Higher principal meridian (dioptres) (+ or -) Mean sphere tolerance (dioptres) ISO >3.00 to >6.00 to >9.00 to >12.00 to > ORLAB 2011 Page 11 of 13 AS and ISO 21987:2011

12 Table 3 Tolerances on cylindrical power Ordered 0.00 cyl Ordered 0.25 to 0.75 cyl Ordered 1.00 to 4.00 cyl Ordered 4.25 to 6.00 cyl Ordered > 6.00 cyl cyl limit cyl tolerance cyl tolerance cyl tolerance cyl tolerance Cylinder power (dioptres) ISO ISO ISO AS ISO ISO >0.00 to >3.00 to >6.00 to >9.00 to >12.00 to > Table 4 Tolerances on cylindrical axis Cylinder axis tolerance Cylindrical power (dioptre) ISO > ORLAB 2011 Page 12 of 13 AS and ISO 21987:2011

13 Page 13 of 13 Table 5 Tolerances on prism power (not progressive or degressive) Principal power Horizontal prism tolerance ISO base out base in Principal power Vertical prism tolerance ISO > *power > *power > ORLAB 2011 Page 13 of 13 AS and ISO 21987:2011