Dear J., Thanks for your elaborate answer, I really appreciate you taking the time.
Unfortunately I can't do all the tests you suggest(or have contact lenses fitted) with my son, since he's only 4 years old. It's hard enough for him to describe whether he sees better or not with his glasses, let alone the subtle differences you describe. Is there anything I can do to measure the index by shining a light through it and measuring entrance and exit angles, or something along those lines? (or perhaps something with distance between different colours, or measuring the focal distance by using it to concentrate sunlight in a single spot?) The online shop is probably the most reputable one for quality, and claims to have several optometrists working for him, and getting the lenses only from a specific factory, so normally they should be the same. The customer service lady has checked, (at least that's what she claims), at my request, with the people who make the glasses, and this expert confirms that it is due to the bigger frame size that the lenses are so much thicker. In my view there are a few options: a) They used the wrong index, and don't want to admit it or have no accurate records to check. b) They used the correct index, but forgot the surfacing. Is that possible/likely? c) Due to the (albeit small) difference in size they had to go up one whole 'size' in starting material, causing a much bigger than proportional difference. But why don't they then explain it like that, then it would be fine d) different origins of the lenses as suggested by Chuck(but i find this unlikely, as explained above) Your suggestion about Eyebuydirect is not so bad. However, I found that there are only very few online shops (at most two), that do frame sizes suitable for 4 year olds, AND sphericals higher than +8. Most seem to put the limit at +8. Eyebuydirect fails on the first criterion. Basically, the frame I ordered him (42 width, 17 bridge, 125 temple) is already close to the upper limit of not looking ridiculous on him, Eyebuydirect offers nothing that small. Thanks again, and best regards BertJan On Apr 17, 9:21 am, "J. Evan" <[email protected]> wrote: > I second Chuck's comment that the same glasses shop can and does use > different suppliers and even different labs, this is quite possibly > the situation. > > Although it's possible, I don't necessarily agree with Paul that a > lower index lens was used. It would be noticeable for the wearer in > such a high hyperopic correction (not so much for high myopic), your > son would notice a difference in magnification when viewing near > objects. Have him do a test between both glasses - view an object in > front of him (something with a sharp edge works best) about 6 feet > away, keep his eyes on the object and turn his head side to side, to > the farthest extreme of his peripheral vision. This will allow him to > notice the aspheric 'shape' or design - the least amount of distortion > he see's, the better design of the aspheric lens (generally). Now do > the same test but this time tilt the head up and down until he looks > over the glasses (the unapproving school teacher look). By moving the > head up and down just slightly he will see how much magnification is > in the lens. The difference will be slight between the different > lenses, or maybe not at all. But if he notices a difference then the > lenses that appears less magnified might have a higher index rating. > > Surfacing is when they machine or "sand down" (think woodworking) the > additional thickness of the lens after it's cut for shape. All lenses > that are +4.00 and above need this additional surfacing because nearly > all lenses below a +4.00 are what they call 'stock lenses' - that is a > lens that is already thinned at the edges that all they have to do is > cut to shape. See the nice tutorial at the 'how stuff works' > website:http://science.howstuffworks.com/lens7.htm > > The question now is what can you do about it? > > Well, probably nothing about the current lenses, as long as the > prescription is correct, they technically have delivered the product > you ordered. Unless you speak with the Lab directly, the sales people > you deal with over email/phone likely know little about the surfacing > procedures and would not be forthcoming even if they were. > > You could take advantage of the EyeBuyDirect 30% off sale on the > GlassyEyes site and get him a pair of 1.74 index lenses for only $78. > That's 30-40% less than almost anywhere else. It's the highest index > commonly available and you could always rest easy that you've done > everything you could to reduce his trauma at school. > > Otherwise, try spending a few months with a qualified optician to fit > contact lenses. I've spent years trying to find a workable solution > without much success (not many manufacturers produce lenses in high > plus corrections), but he might have better luck. > > On Apr 16, 9:28 pm, BJ <[email protected]> wrote: > > > > > In my case the lenses are actually twice the same quality from the > > same manufacturer. > > > I had heard this term 'surfacing' before, but am not quite sure what > > it means. So it is actually a way of making thinner lenses? > > > It could be an explanation. But I find that strange, why would the > > same company do it in some cases, and not in other cases? > > > BertJan- Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ 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. 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