ISO 11984 pdf download.Ophthalmic optics — Contact lenses — Determination of rigid lens flexure and breakage
1 Scope
This International Standard describes a method for determining the flexural properties of finished rigid contact lenses when tested under specified conditions. The existence of this International Standard does not imply in any way that the testing of contact lenses for flexure and breakage is a requirement.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard 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 8320:1 986, Optics and optical instruments — Contact lenses — Vocabulary and symbols. ISO 9337-1 , Contact lenses — Determination of back vertex power — Part 1 : Method using focimeter with manual focusing. ISO 9337-2, Contact lenses — Determination of back vertex power — Part 2: Measurement on contact lenses immersed in saline. ISO 9338:1 996, Optics and optical instruments — Contact lenses — Determination of diameters. ISO 9339-1 , Optics and optical instruments — Contact lenses — Determination of thickness — Part 1 : Rigid contact lenses. ISO 1 0338:1 996, Optics and optical instruments — Contact lenses — Determination of curvature. ISO 1 0344:1 996, Optics and optical instruments — Contact lenses — Saline solution for contact lens testing.
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 8320 apply, together with the following. 3.1 flexural deformation reduction of the diameter of the contact lens due to a load applied to the edge of the contact lens, perpendicular to the lens axis, to induce flexure NOTE It is expressed as a percentage of the original lens diameter.3.3 flexural deformation strength load applied at the contact lens edge at a specific point during a flexural loading test NOTE For the purposes of this International Standard, the flexural deformation strength at rupture and at a 30 % deformation of the contact lens are of primary importance. 3.4 conditioning procedure intended to bring a sample or test specimen into a state of equilibrium with regard to hydration and temperature 3.5 vertex sphere imaginary spherical surface touching the back vertex of the lens NOTE The radius of curvature of the vertex sphere is the same as the back optic zone radius (r 0 ) or the apical radius of a contact lens with an aspheric back optic zone (ISO 8320).
4 Test method
4.1 Principle The test, which is a destructive test, applies an increasing load at the edge of a rigid contact lens across the total diameter until ultimately the test sample fractures. The test is carried out in an apparatus which allows the load and flexural deformation to be monitored continuously. Both the flexural deformation strength and flexural deformation at rupture are determined, as well as flexural deformation strength at 30 % deformation. The latter is derived from the flexural load-deformation curve. Both normal production and specially constructed rigid contact lenses can be tested. 4.2 Sampling 4.2.1 General requirements In order to demonstrate the degree of resistance to breakage by the material, general samples for testing shall be normal, commercially available rigid, single-vision contact lenses and shall not have been specially treated or adjusted. Contact lenses which have toroidal zones or truncations shall not be used. The specified back vertex power (F’ v ) shall be the same for all samples and shall be between +0,50 D and –0,50 D. The specified back optic zone radius (r 0 ), or radius of the vertex sphere, shall be the same for all samples and shall be between 7,75 mm and 7,85 mm.