ISO/TR 21958:2019 pdf download – Ophthalmic optics — Review of the test methods used to assess scratch and abrasion resistance of spectacle lenses.
ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https: //www .iso .org/obp — IEC Electropedia: available at http: //www .electropedia .org/ 4 Background As the spectacle lens market shifted from glass toward plastic in the 1970s, the demand for improved abrasion resistant coatings for plastic lenses resulted in the need to assess and compare the performance of the new coatings in the market. A number of very different abrasion test methods were developed over the years which employ a variety of ways to abrade the lens. Each method uses a unique scratch or abrasion mechanism which affects how the lens is assessed for its ability to resist damage. In addition, different methods of assessment of test lens surface damage are used by these test methods. Together, the different mechanisms of abrading and the different assessment methods often result in dramatically different ranking and rating of the performances of lens surfaces that do not reflect marketplace performance and the experience of wearers in real life conditions. Considerable national and ISO standardization activity was directed to find one single test method that would reliably predict wearer experience or market performance. After much work, it was realized this goal could not be achieved and that work was abandoned. In its place an ISO standard (ISO 8980-5) was successfully developed with a methodology capable of determining whether a lens surface claimed to be abrasion resistant could achieve a basic performance level. This test method follows the only known approach avoiding the possibility of using the standard test to rank products in the market. Further work followed the successful publishing of ISO 8980-5, this time with the aim of creating a standard for “enhanced abrasion resistance” at a higher level than “basic level”.
5 Mechanisms of mechanical abrasion and scratching of lens surfaces 5.1 Discussion and scratch mechanisms When attempting to classify and quantify damage to a lens surface, the spectacle industry itself has differences in opinions on the definitions, descriptions and classifications of damage types. A standardized method for assessing and quantifying such damage is therefore an extremely complex activity that will always have different views on interpretation of test results. Two typical terms used in the spectacle lens industry to describe lens surface damage are ‘abrasion’ and ‘scratching’. No single agreed definitions exist for these terms in the industry, however basic descriptions could be: — SCRATCHING – A process of degrading from a pristine surface of a lens caused by initial contact / impact of an object on a lens surface and then friction / motion of the object across the lens surface. synonyms: score, abrade, scrape, roughen, scuff (up), lacerate, groove, gash, engrave, incise, gouge — ABRASION – A process of degrading from a pristine surface of a lens caused by the pitting or wearing away of the surface. synonyms: wearing away/down, wearing, erosion, scraping, corrosion, being eaten away, chafing, rubbing, stripping, flaying, excoriation