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Medical Forum / General / Vision / July 2005Glass glasses and hot coatings
I have been using antireflection coated plastic lenses now for about 18 months. For a while, I was surprised by how well they were surviving cleaning. Now, scratches and fuzziness is beginning to show up. How easy is it to get real glass lens spectacles these days? It seems the plastic is still being marketed more strongly than glass. Is it difficult to to get hard coatings such as quarter-wave (or higher performance designs) magnesium fluoride deposited upon hot glass lenses? How do I go about doing so without getting supercilious lectures on why the customer is totally ignorant about such matters? If I want computer glasses, how do I go about getting my distance/reading prescription modified according my specifications, again without having a nanny OD or ophthalmologist telling me that they know better. In my case I would want about a 1.75D addition to my distance prescription with a 1.25D or 1.50D bifocal add. I know that one argument for plastic is that it will make for lighter spectacles. In my case, after double cataract surgery, the thickness of external corrective lenses can be greatly reduced from what used to be necessary. Bill > I have been using antireflection coated plastic lenses now for about 18 > months. For a while, I was surprised by how well they were surviving > cleaning. Now, scratches and fuzziness is beginning to show up. 18 mos isn't bad, and the coatings are getting better (and more expensive) all the time. There are lots of high quality coatings to choose from these days. > How easy is it to get real glass lens spectacles these days? It seems the > plastic is still being marketed more strongly than glass. Not yet on the black market. No problem, if you don't mind the extra weight or your nose and the additional safety risk (they will be hardened, if purchased in the USA, but can still break into sharp, eye cutting projectiles if hit hard enough. Is it difficult to > to get hard coatings such as quarter-wave (or higher performance designs) > magnesium fluoride deposited upon hot glass lenses? How do I go about doing > so without getting supercilious lectures on why the customer is totally > ignorant about such matters? Glass is the most scratch resistant lens material on the planet, and the AR coatings that go on them are equally tough. No problem. > If I want computer glasses, how do I go about getting my distance/reading > prescription modified according my specifications, again without having a > nanny OD or ophthalmologist telling me that they know better. In my case I > would want about a 1.75D addition to my distance prescription with a 1.25D > or 1.50D bifocal add. OK if you like your monitor "in your face". I prefer a +1.25 add for the upper part, so I can sit farther back from the monitor, a strong personal preference. Plus you get greater depth of focus. And why so strong in the lower? Unless you're less than 20/20 best corrected, you may regret the narrow depth of focus there too. > I know that one argument for plastic is that it will make for lighter > spectacles. In my case, after double cataract surgery, the thickness of > external corrective lenses can be greatly reduced from what used to be > necessary. True, especially for computer glasses (I assume you WILL NOT be using these to run a lathe or some such activity?)> w.stacy, o.d. <snip> > No problem, if you don't mind the extra > weight or your nose > w.stacy, o.d. Funny enough, the people who discouraged me from getting glass lenses used this as their primary argument. Weight. For the first few days I *did* notice the difference, but honestly, after wearing the glasses for ~ 2 mo. or so, I've gotten accustomed to it (and this is with an Rx in the mid teens ... should be even easier to do with a lower Rx). But anyway ... > <snip> >> No problem, if you don't mind the extra [quoted text clipped - 8 lines] > with an Rx in the mid teens ... should be even easier to > do with a lower Rx). But anyway ... I wore glass (non-Rx) sunglasses for many years. I was on the road a lot. Polarized, darkest neutral grey with a double gradient mirror. Ray Ban used to make a decent one until the hardening law in ('64?). Somewhat more recently Nikon made very excellent sunglasses (both lens and frame) with glass lenses and all the coatings and stuff inside the sandwich. The weight became very noticeable with all day wear in hot humid environments (golf). Once my face got oily and sweaty I couldn't keep them from sliding off my nose. I recently switched to Rudy Project sunglasses because of that and becoming a bit more safety concious. They're supposed to have really good optical characteristics? The glass lenses were significantly better. I've stayed with the plastic for the other reasons. -Quick > The weight became very noticeable with all day wear in > hot humid environments (golf). Once my face got oily and > sweaty I couldn't keep them from sliding off my nose. Although I don't play golf, the whether in Toronto has definitely been hot and humid lately. I don't think I'll be going out for an extended period of time though. ;) But yeah, I could see how that would be a problem. Glass lenses fit my lifestyle quite well. I still think what everyone was telling me was an exaggerated version of the truth. Perhaps in certain circumstances they are noticeably heavy, but in most of the situations I encounter on a daily basis, they are perfectly fine. Than you for a very informative reply On 7/17/05 9:45 PM, in article MtGCe.4376$_%4.442@newssvr14.news.prodigy.com, "William Stacy" <wstacy@obase.net> wrote: <snip a bit> >> If I want computer glasses, how do I go about getting my distance/reading >> prescription modified according my specifications, again without having a [quoted text clipped - 7 lines] > strong in the lower? Unless you're less than 20/20 best corrected, you > may regret the narrow depth of focus there too. With my monitor at a distance I liked, I measured distance to it at about 57 or 58 cm. If my distance correction is optimum and accurate, then 1.75D is just about right to move the screen to infinity. Often, while I am at my computer, I want to read smaller print or read instructions in dimmer than usual light. Seldom am I actually typing copy from a manuscript or a book. I like the extra bit of magnification. With intraocular implants, I get no accommodation anyway. >> I know that one argument for plastic is that it will make for lighter >> spectacles. In my case, after double cataract surgery, the thickness of [quoted text clipped - 3 lines] > True, especially for computer glasses (I assume you WILL NOT be using > these to run a lathe or some such activity?)> Moreover, for my computer, I will probably get frames with somewhat smaller area than I would for general purpose wear. I must admit that I have been tempted to get the combination lathe, mill, and drill press made in China as sold by Harbor Freight. So far, I have resisted that impulse. I would probably get polycarbonate (Lexan) safety goggles if I ever were to yield to that temptation. Bill > With my monitor at a distance I liked, I measured distance to it at about 57 > or 58 cm. If my distance correction is optimum and accurate, then 1.75D is > just about right to move the screen to infinity. You might not be thinking of depth of focus (aka depth of field) effects. For the sake of simplicity, I'm going to assume a depth of focus of .50 in the area of a 1.75 add, assuming normal illumination and pupil size. That means you see clearly .25 D. on either side of the focal distance. So for a 1.75 add, you would be clear from about 50 cm to about 67 cm, or a 17 mm range of clarity. But let's say you chose a 1.50 add. Similar calculations mean that your range is from 57 cm out to 80 cm, or about 23 cm range of clarity. This is why I tend to underprescribe a bit for computer use; it gives a little more flexibility. Even though you have no accommodation, you have this depth which you can think of as the ability to focus + or - by .25, maybe even .50 D., depending on pupil size and illumination. I also prefer people to push the monitor away as far as is convenient, for convergence comfort. > I must admit that I have been tempted to get the combination lathe, mill, > and drill press made in China as sold by Harbor Freight. So far, I have > resisted that impulse. I would probably get polycarbonate (Lexan) safety > goggles if I ever were to yield to that temptation. Better yet, use Trivex for that. And stay away from China made machine tools. They stink because the metal is too soft. Looks nice, but doesn't hold up. Some day their tool quality will come up, but not yet. w.stacy, o.d. |
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