I have two year old full rim glasses with +5.00 -2.25 180 - lens size 48x28 - made with Seiko 1.67 lenses at a B&M ($400). Recently I bought a pair of Zenni full rim, with +4.75 -2.00 180 - lens size 50x28 - made with Zenni's 1.67 lenses ($58). Both are virtually identical in lens shape (not more square or more rounded).
With my digital calipers, my 1.67 B&M lenses measure: 1.83mm at the thinnest (top outside edge) and 3.92mm at the thickest (center bottom). My new Zenni lenses measure 2.61mm at the thinnest (top outside edge) and 4.33mm at the thickest (center bottom). There will always be variation in the lens manufacturer, the aspheric design and most importantly the additional surfacing needed for all prescription lenses above +4.00. I suspect that the different labs surface differently and that's where your problem lies. The manufacturer and the lab always can fall back on the fact that the lenses were made to 'spec', that is, they're your correct prescription. Technically they're probably right as there is no specification standard (as far as I know) for surfacing for high plus prescriptions. That leaves them plenty of leeway to make your lenses as thick or as thin as they want. I know that some lens manufacturers have specific minimums for lens thickness (usually 1.5-2.5mm) - this could also be a factor. It would be great if an actual lab engineer or technician was a member of these boards so we could better answer these types of questions. On Apr 15, 9:18 pm, BJ <[email protected]> wrote: > Dear All, > > I have a serious disagreement with one of the most reputable online > glasses shops. I will not name them until I am certain that I am > right, but for that I need your help. > > Last year I order a pair of glasses for my son with lens size 41*21 > mm, prescription +8.5, Cyl -2.5, axis 175, lens index 1.67. I was very > pleased with them, they were very thin, approximately 4 mm at the > thickest point at the edge, and circa 4.5-5 mm total thickness. They > appeared well made, no complaints. > > In March 2009 I ordered the same prescription and lenses quality and > index, but this time with a frame size 42*25 mm, so only 1 mm wider. > This time however, the lenses were circa 2 mm thicker, both at the > edge as well as total thickness. This is 50% more!!. I was > dissappointed with this, I don't want my son to be teased in school > for wearing jam jars. > > I complained, and after several messages to and fro and even a side by > side photograph, the company says they delivered the correct product > and maintains that this difference in lens thickness is due to the > difference in frame size. > > I, on the other hand, agree that with a slightly bigger frame comes a > slightly thicker lense, but surely not 50% more! > > I also checked the lens thickness > athttp://www.opticampus.com/tools/thickness.php.The > first pair is more or less in line with opticampus, whereas the second > is way out of line, it is much too thick. > > So, is there anybody who can give a sensible opinion on this? > > thanks, > > BertJan --~--~---------~--~----~------------~-------~--~----~ Check us out at the oft-updated http://www.glassyeyes.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 -~----------~----~----~----~------~----~------~--~---
