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Medical Forum / General / Vision / August 2006plastic vs. glass
My grandmother who is 82 has the belief that she must have glass for her eyeglasses. That plastic will be blurry and unclear. The problem is that she only has vision in one eye and I am concerned that at 82 if she were to fall or be in some sort of an accident that the glass could break and if it were to get into her only good eye lead to partial or complete blindness. Is there any truth to her belief that plastic is not as clear as glass? How about the difference in breakability, is there any? She is an artist, a painter and losing her vision completely would probably lead to an early death. Cost is an issue, we cannot afford much. Her prescription is for progressive lenses (which she's had before) and the second eye "balance" ... she learned she needed new lenses by not being able to pass the eye exam at the drivers licensing. She originally went to an opthamologist (I think that's right, the eye DR not the vision specialist). When she got her prescription from him filled the new lenses were very blurry and she could not see out of them. Her old eye glasses seemed clear and the new eyeglasses were terrible. They were plastic versus the glass that she was used to. On the outgoing paperwork the prescription did not match. The store manager said that the opthamologists write their prescriptions differently than optologists (I apologize if I'm masacreing your titles). Any help would be appreciated. >My grandmother who is 82 has the belief that she must have glass for her >eyeglasses. That plastic will be blurry and unclear. The problem is that she [quoted text clipped - 22 lines] > >Any help would be appreciated. >My grandmother who is 82 has the belief that she must have glass for her >eyeglasses. That plastic will be blurry and unclear. The problem is that she [quoted text clipped - 22 lines] > >Any help would be appreciated. > My grandmother who is 82 has the belief that she must have glass for her > eyeglasses. That plastic will be blurry and unclear. The problem is that [quoted text clipped - 32 lines] > > Any help would be appreciated. In my experience, many ophthalmologists (MD's) over-prescribe compared to optometrist (OD's). This is one thing that can cause blurry vision. Another thing that can cause blurry vision, is a lens with poor optical quality, such a polycarb. This is the worst lens possible for someone with a strong Rx wearing progressive lenses. Unfortunately, it is over-dispensed by many opticians. A mediocre brand of progressive lenses (talking about the lens design, not the material) can also cause less than optimal vision. especially with a strong Rx. The last (but not least) factor is the accuracy of the fitting (frame, lens, etc). This is hard to gauge on a newsgroup. If possible, I would post on this forum her old and new Rx, the exact manufacturer, model, and lens material of her new progressives. >In my experience, many ophthalmologists (MD's) over-prescribe compared to >optometrist (OD's). This is one thing that can cause blurry vision. My experience with opthalamosts doing refraction isn't so great. So I've come to this as possible reason: Don't opthamologists (sp?) make most of their money performing *surgery* (on the eye)? If so, then perhaps for at least some of them, refraction is a "loss leader" that gets people "in the door" -- then when a certain number of them need surgery, they're already your patients! Reasonable? David >My experience with opthalamosts doing refraction isn't so great. I think in general ophthalmologists (OMDs) don't refract as good as most optometrists (ODs). Likewise, I believe that most ODs aren't as good at medical eye care as most OMDs. And I speak as an OD. >So I've come to this as possible reason: >Don't opthamologists (sp?) make most of their money performing >*surgery* (on the eye)? Most OMDs make the majority of their money doing medical and surgical eye care, rather than refractive eye care. >If so, then perhaps for at least some of them, refraction is a "loss >leader" that gets people "in the door" -- then when a certain number >of them need surgery, they're already your patients! Well, all eye care professionals need to realize that a lot of "ocular disease" can be "cured" with a great and careful refraction. And all eye care professionals need to realize that even in asymptometic 20/20 patients, you will need to carefully screen for disease. That being said... My belief is that a lot of OMDs look down at refracting. They believe it is the domain of "ancillary health care professionals" (ODs, ophthalmic technicians). They believe it to be boring and not to require a lot of skill. Many don't do it a lot. They may only refract in cases when the technician couldn't obtain VA that is consistent with the eye findings. Remember, the three most important qualities of any doctor (IMHO): o They have a lot of knowledge. o They are highly skilled at doing things. o They have and exercise great judgement. And skill comes from doing things a lot. OMDs want to blast (with a laser), cut (with a scalpel), medicate, etc. That's what they want to do. That what they were trained for. That's what they're supposed to be the experts at. In general, when ODs refract, they strive for vision that is clear, comfortable and effortless. In general, when OMDs refract, they strive for to obtain 20/20. Hope that helps! >My grandmother who is 82 has the belief that she must have glass for her >eyeglasses. That plastic will be blurry and unclear. The problem is that she >only has vision in one eye and I am concerned that at 82 if she were to fall >or be in some sort of an accident that the glass could break and if it were >to get into her only good eye lead to partial or complete blindness. That is a valid concern. IMHO, someone like her (i.e., a monocular patient) should NOT be wearing glass lenses in probably every case. >Is there any truth to her belief that plastic is not as clear as glass? Yes. However, the difference is negligible in the vast majority of cases. >How about the difference in breakability, is there any? Plastic scratches easier while glass (in general) is more likely to break. [snip] >Cost is an issue, we cannot afford much. Her prescription is for progressive >lenses (which she's had before) and the second eye "balance" ... she learned >she needed new lenses by not being able to pass the eye exam at the drivers >licensing. Plastic progressives, in general, cost less than glass ones. >She originally went to an opthamologist (I think that's right, the eye DR not >the vision specialist). When she got her prescription from him filled the new >lenses were very blurry and she could not see out of them. Her old eye >glasses seemed clear and the new eyeglasses were terrible. They were plastic >versus the glass that she was used to. On the outgoing paperwork the >prescription did not match. It is far more likely her complaint was because the prescriptions were different in power versus due to plastic vs. glass lenses. >The store manager said that the opthamologists write their >prescriptions differently than optologists (I apologize if I'm >masacreing your titles). He was probably talking about minus cylinder vs plus cylinder notation. Historically, most ODs have used minus cylinder phoropters while most OMDs have used plus cylinder phoropters. But that distinction has blurred a lot in recent. >Is there any truth to her belief that plastic is not as clear as glass? CR39 plastic, index 1.498, has a light transmission of 92.4%. Crown glass, index 1.523, has a light transmission 91.6%. The Abbe number of CR39 is 57.8, crown glass is 58.5. You should not be able to detect any differences in quality of vision if the lenses are processed properly. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France On 8/16/06 10:10 AM, in article 0aj6e2p15h9265vcdcf1a7botdj1oqalcs@4ax.com, >> Is there any truth to her belief that plastic is not as clear as glass? > [quoted text clipped - 14 lines] > "If a million people believe a foolish thing, it is still a foolish thing." > - Anatole France I think this is a confused post. If you calculate the Fresnel reflectivity for the given index and subtract that from one, you get the quoted values for "transmission" for a single lens air interface. They have nothing to do with actual absorption in the lens material. AR coating will change those values anyway Bill. -- Ferme le Bush > On 8/16/06 10:10 AM, in article 0aj6e2p15h9265vcdcf1a7botdj1oqalcs@4ax.com, > > ... You should not be able to detect any differences in quality of vision if the > > lenses are processed properly. > ... I think this is a confused post. Seems a straight answer inspires doubt. Why does the patient prefer to think that stuff the Dr. (or other qualified health-care/eye-care professional does) deals with is complicated beyond lay comprehension. > If you calculate the Fresnel reflectivity for the given index and subtract > that from one, you get the quoted values for "transmission" for a single > lens air interface. They have nothing to do with actual absorption in the > lens material. AR coating will change those values anyway. Well, you could look at it this way: if a lens material were absorptive, you could notice it by visually examining it. Have you ever seen eyeglass material which appeared gray or colored, short of being coated or tinted? (And, if you could not notice it, what difference would it make, anyway?) -- Dicky >On 8/16/06 10:10 AM, in article 0aj6e2p15h9265vcdcf1a7botdj1oqalcs@4ax.com, > [quoted text clipped - 26 lines] >Bill. >-- Ferme le Bush The numbers I posted are the actual luminous transmittance, or the amount of light that passes through the lens, averaged over the visible spectrum using a tungsten filament lamp and overcast sky as light sources. The information comes from "Spectral Transmittance of Lens Materials" by Daniel Torgersen 1998. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr On 8/17/06 12:03 PM, in article v829e2p16252d0t5h1cti4htebdea4qgds@4ax.com, > The numbers I posted are the actual luminous transmittance, or the amount of > light that passes through the lens, averaged over the visible spectrum using a > tungsten filament lamp and overcast sky as light sources. The information > comes > from "Spectral Transmittance of Lens Materials" by Daniel Torgersen 1998. Usually, the Fresnel loss is separated from the extinction loss. Bill -- Ferme le Bush >On 8/17/06 12:03 PM, in article v829e2p16252d0t5h1cti4htebdea4qgds@4ax.com, > [quoted text clipped - 8 lines] >Bill >-- Ferme le Bush Apparently absorption is negligible with clear ophthalmic lenses. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ The bitterness of poor quality remains long after the sweetness of low price has waned. On 8/17/06 4:02 PM, in article q2t9e21u4rvi5va8gafrnkl5fh1etrq78o@4ax.com, > Apparently absorption is negligible with clear ophthalmic lenses. Nevertheless, Schott lists it as a function of wavelength for their optical glasses. Usually, Ophthalmic lenses are thin enough so that absorption is not a problem. Bill -- Ferme le Bush Everyone can stop overanylizing now. She's 82, get her what she wants. She's more than earned that right. >My grandmother who is 82 has the belief that she must have glass for her >eyeglasses. That plastic will be blurry and unclear. The problem is that she >only has vision in one eye and I am concerned that at 82 if she were to fall >or be in some sort of an accident that the glass could break and if it were >to get into her only good eye lead to partial or complete blindness. Ask if Trivex (virtually unbreakable lens plastic) would be suitable for her Rx and lens design needs. Polycarbonate might be ok for some Rxs. >Is there any truth to her belief that plastic is not as clear as glass? How >about the difference in breakability, is there any? She is an artist, a >painter and losing her vision completely would probably lead to an early >death. She will see better when painting if the eyeglasses are designed to offer clear vision at the distance she is working. This might require a separate pair. >Cost is an issue, we cannot afford much. Her prescription is for progressive >lenses (which she's had before) and the second eye "balance" ... she learned >she needed new lenses by not being able to pass the eye exam at the drivers >licensing. Then a change to lined bifocals/trifocals should be considered for the potential of increased quality of vision as well as substantially reduced cost, if she is willing to change. >She originally went to an opthamologist (I think that's right, the eye DR not >the vision specialist). When she got her prescription from him filled the new >lenses were very blurry and she could not see out of them. Her old eye >glasses seemed clear and the new eyeglasses were terrible. Sometimes new Rxs will cause some distances to be less clear in exchange for more clarity at other distances. Sometimes the lenses are made improperly, and on occasion the Rx just might not workable. Not enough information to make that judgement here, but there is a reason why this happened, and an experienced optician should be able find the problem. >Any help would be appreciated. Hope this helps, Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France |
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