ISO 11979-2:1999 download

07-09-2021 comment

ISO 11979-2:1999 download.Ophthalmic implants — Intraocular lenses — Part 2: Optical properties and test methods TECHNICAL CORRIGENDUM 1.
This part of ISO 11979 contams several test methods for which associated requirements are given and one test method for which no requirement is foi-mulated. The former are directly connected to the optical functions of intraocular lenses. The latter, the test for spectral transmittance, has been provided for those interested in information about UV transmission and in specdic situabons, e.g. when using laser light sources for medical diagnosis and treatment.
Extensive interlaboratory testing has been carried out before setting the limits specified. Some basic problems were encountered.
The accuracy in the determination of dioptric power has an error that is not negligible in relation to the halt-dioptre
steps in which intraocular lenses are commonly labelled. The dioptric power tolerances take this tact into account.
Hence the limits set may lead to some overlap into the next labelled power, especially for high dioptre lenses.
Reference (1) gives further discussion on this subject.
The majority of tenses hitherto implanted have been made from poly(methyl methacrylate) (PMMA), and were qualified using the method described in annex B. Thus the general clinical experience is associated with this level. The method in annex B is limited in its applicability, however. The limits for the more general method in annex C have been set in terms of MTF in an eye model, following two approaches. The first is by correlation to the method and limit in annex B. Further discussion can be found in reference [2). The second is set as a percentage of what is calculated as theoretical maximum for the design, with the rationale that a minimum level of manufacturing accuracy be guaranteed. For common PMMA Lenses, these two bmits correspond well with each other. For lenses made of materials with lower refractive index, or with certain shape factors, or for extreme power lenses in general, the latter limit Is lower than the former. However, such lenses are already in use, indicating clinical acceptance. The question arises Which is the absolute lowest limit that is compatible with good vision. No definite answer can be found, but following clinical data presented to the working group, an absolute lower limit has been set for the calculation method.
NOTE It always was and still is the intention of the Technical Committees SOITC 172./SC 7 and CEN/IC 170 to prepare identical ISO and CEN (European Committee for Standardization) standards on intraociiar lenses. However, during the preparation of part 7 of this series, problems were encountered with normative references to the existing ISO 14155 and EN 540 horizontal standards on clinical :nvestigation of mec*cal devices, which are similar but not identical,
ISO and CEN pflnciples concerning normative references made it impossible to continue the preparation of identical International and European Standards on the clinical investigation of intraocular lenses. As a result, two different standards senes have had to be prepared. For this part of ISO 11979. identical versions exist for ISO and CEN (ISO 11979.2 and EN ISO 11979-2). For those parts where no identical versions exist, it is the Wilention of ISO/TC 172/SC 7 and CEN/TC 170 to revise these standards with the ooal to end tie with identical ones as soon as identical ISO arid CEN horizontal standards on
This part of ISO 11979 specifies requirements and test methods for certain optical properties of intraocular lenses (lOLs).
It Is applicable but not limited to non-toric, monolocal intraocular lenses intended fo implantation into the anterior segment of the human eye, excluding corneal implants.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of ISO 11979. For dated references, subsequent amendments to, or revisions of. any of these publications do not apply. However, parties to agreements based on this part of ISO 11979 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards.
ISO 6328: _1), Photography — Photographic matenals — Determination of ISO resolving power.
ISO 9334:1995, Optics and optical instruments — Optical transfer function — Definitions and mathematical relationships.
ISO 9335:1995, Optics and optical instruments — Optical transfer function — Principles and procedures of measurement.
ISO 11979-1:1999, Ophthalmic implants — Intraocular lenses — Pait 1: Vocabulary. U.S. Mu Std 150-A-1961, Photographic lenses.
3 Terms and definitions
For the purposes of this part of ISO 11979, the terms and definitions given in ISO 9334 and ISO 11979-1 apply.
NOTE Some dehnitons from ISO 11979-1 are reproduced for information en annex G.
4 RequIrements
4.1 General
All requirements stated below shaH app’y to the Tinisnea product as marketed. t appucable, the lens shaii be positioned as intended for use.
NOTE 1 The methods specified below are reference methods. Alternative methods demonstrated to produce results that are equivalent to those obtained with the reference methods may also be used.
NOTE 2 Any validated procedures that ensure that lOis are within the tolerances specified may be used in quality control.
4.2 Dioptric power
When determined by one of the methods described in annex A, the dioptric power as stated by the manufacturer (e.g. on the label of the 101) shall, in any meridian, be within the tolerance limits specified in Table 1.
NOTE Astigmatism is inplicly mited by the requirement that dioptñc power be within the tderce limIts at Table I in all meridians,
4.3 Imaging quality
Imaging quality shall be determined either according to the method described in annex B or to the method described in annex C.
NOTE The method of annex C is more general. It can be used e.g. for extreme dioptric powers and for materials which swel in aqueous humour, (or which cases the method 01 annex B is not suitable.
a) If determined in accordance with annex B. the resolution efficiency of the IOL shall be no less than 60 % of the diffraction-limited cut-off spatial frequency. In addition, the image shall be free of aberrations other than those due to normal spherical aberration.
b) If determined in accordance with annex C. the modulation transfer function (MTF) value of the system of model eye with IOL shall, at 100 mm1. meet either of the two conditions given below.
1) be greater or equal to 0,43;
2) be greater or equal to 70 % of that calculated as maximum attainable for the system of model eye with the specific IOL design and power in question, but in any case greater or equal to 0,28.
NOTE 1 Spatial frequency has the dimension of reciprocal length, mm1. it is often referred to as line-pan per mm or c/mm. where c denotes cycles.
NOTE 2 The approval levels given above correspond well with each other for PMMA lenses m the range 100 to 300.
NOTE 3 Examples of calculation of maximum attainable MTF at 100 mm-’ are given in C.5.

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