That's interesting. You might be right about that, although, I'm not sure how they were able to keep selling me on hi-index lenses when my prescription was around -3.00.
Thanks for the in-depth report. - Ira On Aug 5, 10:26 am, "J. Evan" <[email protected]> wrote: > I'm not so sure about that Ira. > > I've got five pairs of glasses with 1.67 index lenses of nearly > identical width (+/- 1.0mm). Each one was made at a different lab - > two at a B&M lab in Los Angeles, the others were from Zenni, Coastal > Contacts and another Chinese retailer. Zenni's are by far the thickest > - 2.2mm at the edge, 4.96mm at the center, in a full rim metal frame. > The rimless lenses are about 2mm at the edges and vary from 3.6mm to > 3.9mm at the center. As a reference, I also have a polycarbonate > rimless pair from LBW Eyewear, with lens edges of 2.55mm and a center > thickness of 5.32mm. And, my most recent pair of rimless are 1.74 > index (Coastal Contacts) are 2.0mm thin, 3.4mm thick. > > I've never seen opticians have mockups of the exact same frame and > prescription but in different index lenses - this surely cannot be due > to cost, as we know lenses cost very little to make - I suspect it's > more to protect the labs from having to be consistent. It looks like > labs use different size diameter blanks (65, 70, 75mm) depending on > the application and some do additional surfacing to try and thin the > lens edges. These factors are more likely to blame for the differences > in thicknesses. > > Further to the OP point of US standards being more safety-biased than > everyone else, this is a well known fact, google 'ball drop > test' (http://www.ecpmag.com/1webmagazine/2008/01jan/content/FDA- > impact-resistance.asp). Getting glass lenses made in the US is > extremely difficult - many opticians gasp at the thought of crown > glass lenses - they've been very well indoctrinated by the industry > that they're not safe. Many other retailers won't dispense rimless > frames in anything other than Poly - even though we know very well > that MR-10 1.67 Seiko is just as crack/shatter resistant. > > Just speak with a US lab technician, they'll tell you that they won't > go less than 1.5mm or 2.0mm for a center thickness - when in Germany > and Italy for example, they regularly machine to 1.0mm CT - the UK > might have similar standards. There are clear differences in lab > standards between the US and even Canada - have a look at the > OptiBoards forums and it's well covered. > > You are right that optical center can have a significant impact as > well and that may very well be a factor here. > > J. Evan > > On Aug 5, 4:53 pm, Ira Mitchell <[email protected]> wrote: > > > I'd assume the laws of physics are much more important in this > > instance than those of the United States. > > > Sounds to me like either you didn't get 1.67 or the optical center of > > the lens is further from that "thick edge". > > > - Ira > > > On Aug 4, 2:28 pm, Jon Edwards <[email protected]> wrote: > > > > I have just moved to the US, and bought myself new glasses at > > > Lenscrafters. To my surprise, with an identical prescription (-7.00), > > > identical high-index (1.67) and identical frame size and shape, my US > > > glasses are a good two millimetres thicker at the thickest point. > > > > I'm told that this is because safety standards vary around the world > > > regarding lens cutting, and US lens manufacturers have different > > > standards (presumably because the US is so litigious). Apparently the > > > UK and Hong Kong both cut thinner lenses. > > > > That being so, any insight as to where the lenses are cut for online > > > stores, in general or specifically? And under what standard? > > > > Any information at all very welcome! > > > > Thanks > > > > Jon > > --~--~---------~--~----~------------~-------~--~----~ Check us out at the oft-updated http://glassyeyes.blogspot.com! You received this message because you are subscribed to the Google Groups "GlassyEyes" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/glassyeyes?hl=en -~----------~----~----~----~------~----~------~--~---
