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Medical Forum / General / Vision / September 2007Polycarbonate versus High Index Plastic (1.67) lens help!
Hi all, I just picked up a new pair of glasses from Lenscrafters. They recommended Polycarbonate because it was apparently shatterproof etc etc. My prescription is -5 and -5.25, so I think that's fairly high. The frames are a lot smaller, almost a 40% smaller than my old (13 yr old) frames. Here are some of the problems I'm seeing: 1. Keeping my head facing forward if I try to look at something slighty to the right or left of me, it's blurry. - eg. I can see my computer monitor fine. If look at the phone on my desk, a foot away from the monitor, I can't read the brand name or the function buttons, they're all blurry 2. Reading stuff on my desk, all the print (black) has a yellow outline/halo. (Chromatic Aberration?) Also for #1, when driving if I glance at my driver's side mirror (without turning my head), I can't read the license plate info or for example the word "TAXI" on a taxicab's hood. The Lenscrafters person suggested I get "High Index Plastic", which is a $100 upgrade. I don't want to get those and then find that they are the same as the polycarbonate. Does anyone know if these aberrations that I'm seeing is normal for Polycarbonate? And would high index plastic lenses of 1.67 make a huge difference? What about 1.74? Although, Lenscrafters doesn't carry any lens of 1.74. I think Nikon makes a lens like that but they don't carry Nikon lenses. Any advice would be greatly appreciated! Thanks, Kevin Hello, It is surely obvious then; that the glasses are never a satisfactory substitute for normal vision without glasses, and at best are an immense annyoance although they may correct the condition, and at worst they are of no value at all, and induce harm. Discard the bad and aggravating crutches, learn to see perfectly without glasses. This may be accomplished by playing with the rest methods and imitating the normal eye. http://en.wikisource.org/wiki/Perfect_Sight_Without_Glasses > Discard the bad and aggravating crutches, learn to see perfectly > without glasses. This may be accomplished by playing with the rest > methods and imitating the normal eye. And while you're at it, toss out those orthotic insoles and the knee brace. Next toss out your false teeth and use the rest method to firm up your gums to chew food. No need for the heart pacemaker either, so out with that. Insulin, who needs it? You can control your blood sugar with your mind. Hello, Please, who are you? Yes that is right: you are no one in particular! > Hi all, > [quoted text clipped - 32 lines] > > Kevin Polycarb has the worst optics (lowest abbe value) of any commonly dispensed lens material. It has an refraction index of 1.59. The nearest index plastic is 1.60 which should be much better optically than polycarb, should be about the same cost as polycarb (maybe slightly higher), and should have better optics and much cheaper than 1.67. The only disadvantage with 1.60 compared to 1.67 is that 1.60 will be a little bit thicker and hence a little bit heaver. Personally, I would invoke the 30 day money back guarantee and go to Wal-Mart Optical (if you are very concerned about price) or a good independent optician. Wal-Mart has some fairly good lens materials available to them (although I am not sure about SV lenses) 1.74 is probably overkill for your Rx, and generally speaking the higher the index, the worse the optical quality (except for polycarb, which is the worst at 1.59 index). If you must have safety glasses, find someone who dispenses Trivex material (Hoya Phoenix material is one brand that is made of Trivex).. > > Hi all, > [quoted text clipped - 52 lines] > > - Show quoted text - Hey Mark, Thanks for your response. I thought I had it but after reading your response, I guess I was wrong. The higher the refractive index the worse the optical quality? (Optics in physics was over a decade ago). Basically the issue I have with the current set of lenses (Polycarbonate) is the fact that I can't even move my eyes 15-20 degrees off center and it gets blurry. Also looking down at black&white documentation, most of it has a yellow halo. Would the plastic lens fix those issues at both 1.60 and 1.67 refractive indices? The price doesn't really matter, I would rather get it done right. However, lenscrafters has been kinda disappointing so far. From what I've read one typically doesn't use polycarb lenses for prescriptions of -5 and greater.... well they should have recommended against it. They specifically said "Oh this is the best lens for your prescription and it comes with all the protective coatings blah blah". A co- worker of mine got his frames from Wal-mart for almost the same price I paid for mine at Lenscrafters, so I didn't even look into Wal-mart. As for the money back gaurantee, I'm not 100% sure of that. I know that they will fix any issues and even replace the frame/lens upto 30 days, in my case +10 days because the store manager gave me an extension so I could research the "plastic" lenses. Thanks, Kevin > > Hi all, > [quoted text clipped - 52 lines] > > - Show quoted text - Mark, Thanks for your resposne. I didn't realise that the higher the refractive index the worse the optics. I guess I need to go back to Grade 12 physics, that was eons ago. :-) The issue I have with the current lenses is that if I look 15-20 degrees off center it's all blurry. Also, if I look down at a black&white document, the black print has yellow halos on it. If I got the 1.60 or 1.67 plastic would it eliminate the blurriness and halos? Cost is not really an issue (within reason), I didn't go to Wal-mart because I wanted quality... .but Lenscrafters hasn't proven that they know a whole lot more about optics. From everything I've ready they should have been pushing plastic lenses for a prescription worse than -5, not polycarbonate. A co-worker of mine got a new set of glasses from Walmart and he paid about the same as I did at lenscrafters. About the "30 day money back guarantee", I'm not sure I can do that. I know they will fix whatever is wrong, replace the frames, lenses etc. They might not do a moneyback deal though. In my case the manager of the store extended the 30 days by 10 so that I could research the plastic lenses online. Thanks, Kevin > Mark, > [quoted text clipped - 22 lines] > > Kevin Yes, the higher the index, then generally speaking, the worse the optics. You don't something (thinner lighter lens) for free (optically speaking). The biggest exception is polycarb which at only 1.59 index, it has the worst optics of any commonly dispensed lens, but it is a safety lens. Unless Lenscrafters has changed its policy recently, they offer an unconditional 30 day money back guarantee. Call another LC and ask them. You might look at 1.67 VIZIO ATORIC SINGLE VISION with UTMC (Ultra Tough Multi Coating, which is an AR coat). Or look at similar lens designs from Zeiss or Hoya. Lenscrafters carries mediocre quality lenses. Call around to various optical shops in your area to see what lens they carry. >Hi all, > [quoted text clipped - 16 lines] >(without turning my head), I can't read the license plate info or for >example the word "TAXI" on a taxicab's hood. Both (blur and color) are due to Transverse (or lateral) Chromatic Aberration (TCA). The solution is to use a less dispersive material. Look for lens materials with an Abbe value of at least 36, but in your case, probably because you were wearing cr39 plastic, no lower than 42. The lenses still need to be positioned accurately regardless of the lens design. >The Lenscrafters person suggested I get "High Index Plastic", which is >a $100 upgrade. I don't want to get those and then find that they are >the same as the polycarbonate. Depends on the Abbe of the material. 1.60 is 42, 1.67 is 32, 1.70 is 36, 1.74 is 33. Also consider Trivex (1.53, Abbe about 44), and if you opt for 1.60, I would use Seiko's 1.60 aspheric, due to this lenses lower specific gravity (compared to other 1.60 materials). >Does anyone know if these aberrations that I'm seeing is normal for >Polycarbonate? In some applications, yes. That's also true for other lens materials. > And would high index plastic lenses of 1.67 make a >huge difference? What about 1.74? Not a huge difference. I'd error on the side of better optics. >Although, Lenscrafters doesn't >carry any lens of 1.74. I think Nikon makes a lens like that but >they don't carry Nikon lenses. > >Any advice would be greatly appreciated! The frame selected may also be a factor in the lens choice. Most lenses look thicker in rimless frames, drilled lenses require materials with greater tensile strength. I prefer lightweight glasses; they are much more comfortable, stay in position better, keeping the optics aligned as intended, improving functionality. Thickness is primarily a cosmetic concern. Some thicker lenses can be as lightweight, and sometimes lower in weight, than thin lenses. Discuss your needs with the optician, and tell them to take off their sales hat and put on their optician hat. >Thanks, > >Kevin Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman > >Hi all, > [quoted text clipped - 72 lines] > > - Show quoted text - Robert, Thanks for the information. Do technicians at Lenscrafters even have an optical hat? The comment I got before leaving the store the last time was "We can switch you to a high index plastic, that should make it better if it really bothers you but maybe it's something that you need to get used to..... we could change your frame if you want.". They're not giving me any details around the options. What they need to tell me is why I see blurry outside of the focal area, why the chromatic aberration etc. When I asked if a bigger frame would make a difference, she said "a little but not really". > Depends on the Abbe of the material. 1.60 is 42, 1.67 is 32, 1.70 is 36, 1.74 is 33. Is this for High Index Plastic? Lenscrafters only carries 1.67, so I guess its abbe value 32. The frames I picked are plastic, full frames. So I don't think the thickness matters all that much, not as far as seating it goes anyway. Here's a pair very similar.. http://eyeglasses.go-optic.com/enlarge.asp?id=20312&cat=DFRAMES I might have to just do the 100% refund and go elsewhere since these techs don't seem to be very knowledgable OR even care about the end result. So far it seems like all sales, great fronting but no substance. Kevin > > >Hi all, > [quoted text clipped - 105 lines] > > Kevin Kevin, You can find more info about lenses In the thread "Surprised by OTC Reading Glasses" Read posts by Mark A It is very interesting Lena >Robert, > [quoted text clipped - 3 lines] >it better if it really bothers you but maybe it's something that you >need to get used to..... we could change your frame if you want.". There's some truth to the "getting used to it" part. Not sure what they mean about changing the frame though, unless it's positioning the lenses too far from the eyes, which would increase your awareness of the off-axis blurring. >They're not giving me any details around the options. What they need >to tell me is why I see blurry outside of the focal area, why the >chromatic aberration etc. Better still, the optician should have warned you in advance. >When I asked if a bigger frame would make a difference, she said "a >little but not really". In regards to chromatic aberration, any difference due to lens size would be minor, with the difference leaning towards worse not better. >> Depends on the Abbe of the material. 1.60 is 42, 1.67 is 32, 1.70 is 36, 1.74 is 33. > >Is this for High Index Plastic? In addition to polycarbonate (index 1.59), these are the most common hi-index materials used today. > Lenscrafters only carries 1.67, so >I guess its abbe value 32. Right. >The frames I picked are plastic, full frames. So I don't think the >thickness matters all that much, not as far as seating it goes >anyway. Here's a pair very similar.. > >http://eyeglasses.go-optic.com/enlarge.asp?id=20312&cat=DFRAMES Then you don't need Hi-Index lenses. You would probably appreciate the lighter weight trivex though, and as a bonus, trivex is 15% to 20% thinner than standard plastic, virtually unbreakable, chemical resistant, with substantial UV light protection. Don't polish the edges, and do inquire about anti-reflection coatings. >I might have to just do the 100% refund and go elsewhere since these >techs don't seem to be very knowledgable OR even care about the end >result. So far it seems like all sales, great fronting but no >substance. >Kevin More foam than beer, that's for sure. But that's how it is, on average, at the big boxes. You'll have better luck with the independent doctors and opticians, although you'll still need to ask tough questions to screen out the less knowledgable and experienced opticians. Also check if the optician has an ABO Advanced or Masters Certification. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman > Do technicians at Lenscrafters even have > an optical hat? At best, there is only one decent optician in each Lenscrafters store, and they don't work all the time. That is at best. The rest of the sales people were selling shoes or apparel at a different store in the mall last month. > > Do technicians at Lenscrafters even have > > an optical hat? [quoted text clipped - 4 lines] > The rest of the sales people were selling shoes or apparel at a different > store in the mall last month. Mark What about the plus lenses? Will Low-index +2D lenses (glass or plastic) Look too thick ? > Mark > What about the plus lenses? > Will Low-index +2D lenses (glass or plastic) > Look too thick ? A plus 2.00 lens is moderately weak, and will not be too thick for a mid-index lens (1.53 - 1.60). Plus lenses are thin at the edges and thicker in the middle. Most people who have a problem with thick lenses don't like the edge thickness, which is more of problem for a minus Rx (nearsighted). If cost is big factor, you could even get 1.50 plastic, which has excellent optics, but may not come factory coated (for UV or AR) and is going to be heavier than the others. Don't get any coating that is not factory coated by the lens manufacturer. Glass is really too heavy unless you some special requirement for it. Trivex (Hoya Phoenix) or any 1.60 plastic would be good. The Trivex is a safety lens like polycarb, but with excellent optics. > > Mark > > What about the plus lenses? [quoted text clipped - 14 lines] > (Hoya Phoenix) or any 1.60 plastic would be good. The Trivex is a safety > lens like polycarb, but with excellent optics. Thanks Lena > Hi all, > [quoted text clipped - 3 lines] > The frames are a lot smaller, almost a 40% smaller than my old (13 yr > old) frames. Here are some of the problems I'm seeing: Hi, your prescription is almost identical to mine. I have worn polycarbonate for years because of the durability issue -- I ride motorcycles and cannot accept a material for my glasses that may shatter in the event of an accident. I do not have any of the issues that you discuss and doubt that high-index plastic will make any difference. I am not an eye doctor so thus cannot tell you why you're having problems, just that it's not inherent in the polycarbonate material with your prescription strength. >> Hi all, >> [quoted text clipped - 13 lines] >problems, just that it's not inherent in the polycarbonate material with >your prescription strength. I've seen quite a bit of variability in sensitivity to chroma between eyeglass wearers, some of it related to adaptation, some to the quality and positioning of the optics. It sounds like your lenses were well made and positioned properly. However, there is a clear link (see Mo Jalie and Daniel Torgersen) between TCA and off-axis blur, and is a function of the induced prism from the eccentric gaze and the Abbe value of the lens. Except for some of the super Hi-index glass lenses, Polycarbonate has the lowest Abbe value of all the Hi-index lenses available, and as a result, performs poorly in this area when the lens power is above about four diopters. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman Kevin, I haven't read the lengthy follow-ups to this, but just in case my two cents is worthwhile: Five or seven years ago Lenscrafters recommended me the "Featherwates" polycarbonate lenses, and I could tell something was unusual the moment I put them on (this was not the usual sort of adjustment issues). My vision is around -7.75 and -8.25. If I was not staring directly out of the center of the lenses, everything became blurry, and many things split into a variety of colors in my peripheral vision (most noticeably at a sharp black line against a white). I can't remember if I went back the same day, or the next, but after explaining what was going on, the person at Lenscrafters admitted that a percentage of the population (I forget how much, but enough to be notable, I guess) had this problem with the polycarbonate lenses, and they replaced them for free. (Sorry, I forget what material my glasses are currently made of, instead.) Best of luck solving your problem! To my knowledge the company is, at least, aware of the problem and what lenses to offer that will not cause it. -Sarah |
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