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Medical Forum / General / Vision / December 2004prisms in glasses
How much more would a pair of glasses with prisms in them weigh? Are they restricted to glass or certain kinds of plastic? I have never seen prismatic glasses, and I want to learn more about them, but I'm having trouble finding information on the web. > How much more would a pair of glasses with prisms in them weigh? Are > they > restricted to glass or certain kinds of plastic? I have never seen > prismatic glasses, and I want to learn more about them, but I'm having > trouble finding information on the web. Prism can be added to any lens material. It doesn't necessarily add weight, since one side of the lens is made a little thicker, but the other side might well be thinner. How it works for you will depend more on the frame, and the distance between your pupils, than on which material you use. Wide frames with narrow pupil distance and "base-out" prism will make the outer edges noticeably thicker. Base-in prism might actually make them lighter. Vertical prism (base-up or base-down) may be hard to notice when the vertical dimension of the lenses is shorter than the horizontal. Small amounts of prism, like 1 to 3 prism diopters, won't make much difference. To minimize the effect, choose a frame with each lens approximately centered over your pupils. -MT > Prism can be added to any lens material. It doesn't necessarily add weight, > since one side of the lens is made a little thicker, but the other side [quoted text clipped - 4 lines] > distance and "base-out" prism will make the outer edges noticeably thicker. > Base-in prism might actually make them lighter. I have nystagmus and I was considering this approach. I've read about it on the web, but never had a doctor suggest it to me. I have null points and I am tired of having to move my head to read. Visual acuity is not an issue, for me this is a quality of life issue. I enjoy reading but the way I current read is tiring. Who should I go to, to get prism glasses fitted? Will any optician do? A "low vision" specialist, or will I need to go to a AFB assosciated low-vision specialist? I like the smaller frames that became fashionable a few years ago. For one thing the glasses are smaller and they look better (it's a wierd trend that some of the thick frame lenses are comming back into fashion, especially for women). I'd like to not add alot of weight to my glasses. The amount of prism needed to simulate your null point could be 50 or 100 times the "ordinary" amount used to help binocular alignment, so don't count on a very cosmetic result. How far to one side do you have to look to achieve a relative null point? If it's more than the angle from 12:00 to 1:00 on the clockface, more than 30 degrees, prism may cause too much curved distortion and chromatic aberration and you may decide that simply turning your head works better. I'm sorry I misunderstood you; I didn't realize your purpose for using prism. -MT >> Prism can be added to any lens material. It doesn't necessarily add > weight, [quoted text clipped - 25 lines] > that some of the thick frame lenses are comming back into fashion, > especially for women). I'd like to not add alot of weight to my glasses. > The amount of prism needed to simulate your null point could be 50 or 100 > times the "ordinary" amount used to help binocular alignment, so don't count > on a very cosmetic result. So what you are saying is I'll have to have very thick glasses to achieve any effect? > How far to one side do you have to look to achieve a relative null point? Not too far, it just depends. The main problem I have is having to turn my head when I read. This might be caused by a combination of nystagmus and myopia. I tend to have to get close to things to read. > If it's more than the angle from 12:00 to 1:00 on the clockface, more than > 30 degrees, prism may cause too much curved distortion and chromatic > aberration and you may decide that simply turning your head works better. I'd guess it's about 15 degrees or less. > So what you are saying is I'll have to have very thick glasses to achieve > any effect? Probably, yes, thick on the same side of each lens (left side, left eye and left side, right eye). > Not too far, it just depends. The main problem I have is having to turn > my head when I read. This might be caused by a combination of nystagmus > and > myopia. I tend to have to get close to things to read. It's possible that converging your eyes to see single at near helps suppress your nystagmus, in addition to the effect of looking to one side. Prism will allow you to hold the book straight ahead, while requiring you to look to one side. The result is a more natural posture, maybe drawing less attention, but it would be hard to walk around or drive a car with that much prism unless you wear it constantly and adapt completely. > I'd guess it's about 15 degrees or less. That's a lot more than "ordinary" prism. It'd be noticeable to anyone who looks close at the glasses. -MT > Prism will allow you to hold the book straight ahead, while requiring you to > look to one side. Hold on, I thought prisms would allow a person to read straight ahead., to place the null point in line with the head. Why would one be required to look to one side? > The result is a more natural posture, maybe drawing less > attention, but it would be hard to walk around or drive a car with that much > prism unless you wear it constantly and adapt completely. Why would it be hard to adapt to walking around? I only have a learners permit and I do not plan to drive, at least with the way my current perscription is. From the eye charts, I see about 20/60-20/70 with a null gaze. Also, my binocular vision isn't constant. I have alot of anxiety driving and I've had a few near misses. > > I'd guess it's about 15 degrees or less. > > That's a lot more than "ordinary" prism. It'd be noticeable to anyone who > looks close at the glasses. So they will look like "coke bottle glasses"? I might be able to live with that. I just don't like dealing with glasses sliding down my nose all the time- that I'll have a harder time living with. Going to doctors as a kid alot (for other problems, like a heart defect that was repaired), an optometrist all the time, etc., has really done a head trip on me. And living alone at home with parents is hard too. BTW, I also have small epicanthic folds and my eyes are somewhat light sensitive (I'm not an albino, though, I have my grandmother's light olive German skin and brown hair). Nobody in my family has epicanthic folds. I haven't checked my paternal grandmother or grandfather (all I would have are photos), but the rest of them don't. I think this might be part of some kind of syndrome, but my IQ is above average and I don't have webbed fingers, etc. But the congenital heart defect, epicanthic folds, and nystagmus fit in with a number of syndromes. > Hold on, I thought prisms would allow a person to read straight > ahead., > to place the null point in line with the head. Why would one be > required to look to one side With the prisms, you need to move your eyes to the side to see straight ahead. You eliminated the head turn, but not the eye turn. That's if both bases are in the same direction. With both bases facing out, you need to look near to see far. What city are you in? Maybe I can suggest a doctor. SCott > With the prisms, you need to move your eyes to the side to see straight > ahead. You eliminated the head turn, but not the eye turn. Sounds wierd. So basicly it's shifting around the image? That doesn't really sound like a great solution, though it might be better than nothing. Does wearing prism glasses cause headaches when not wearing them? How would this affect monocular vision, since I don't always see with both eyes? I also have strabismus that alternates depending on what I am doing. I do have the ability to see stereoscopicly but it comes and goes. Ocassionally I find the need to wear an eyepatch over my left eye for a few hours a day if I'm reading or playing games. But my eyes aren't really equal- my left eye is nearsighted but better at up close stuff, whereas my right eye is alot better in distance acuity (when wearing my glasses). Perhaps I need a new perscription but the last two times I've gone for a checkup they haven't changed the perscription any, despite the fact I still feel like one eye is fuzzier than the other. > That's if both bases are in the same direction. With both bases facing > out, you need to look near to see far. > > What city are you in? Maybe I can suggest a doctor. I live in Orlando Have you heard of using high minus contacts combined with high plus lenses as a treatment for nystagmus? Does this work with aquired nystagmus only, or congenital nystagmus? >> With the prisms, you need to move your eyes to the side to see >> straight ahead. You eliminated the head turn, but not the eye turn. [quoted text clipped - 17 lines] > perscription any, despite the fact I still feel like one eye is > fuzzier than the other. The problems with stereo vision would probably mean that base-out prisms won't work for you. Your situation actually sounds very complex. >> That's if both bases are in the same direction. With both bases >> facing out, you need to look near to see far. >> >> What city are you in? Maybe I can suggest a doctor. > > I live in Orlando Sorry, don't know anyone there. > Have you heard of using high minus contacts combined with high plus > lenses > as a treatment for nystagmus? Does this work with aquired nystagmus > only, or congenital nystagmus? The high-minus contacts with high-plus lenses are for acquired nystagmus (and not a very viable treatment, either, because the lenses are uncomfortable). What this method does is optically stabilize images on the back of the eye, even when your eye is moving. While this seems to be exactly what you want to do, it really isn't. Your brain "expects" your eyes to be wiggling, and exactly compensates so that the whole world doesn't appear to you to be shaking all the time (a condition called oscillopsia). Because your brain expects this, if you stabilize your image while your eye is moving, the lens trick you describe actually causes oscillopsia. If you have acquired nystagmus, the world appears to be bouncing around all the time, and this stablization trick works. Interestingly enough, there are patients here and there who develop an acquired nystagmus on top of the congenital nystagmus, and those folks experience oscillopsia. Scott > The problems with stereo vision would probably mean that base-out prisms > won't work for you. Your situation actually sounds very complex. Yeah. I suspected the base-out prisms might not work based on earlier descriptions. The optometrist a few years ago, when I asked about these, said he didn't think it was a good idea, though I've forgotten his exact reasoning. Perhaps he was right. The underlying problems I have are moderate myopia and optic nerve hypoplasia. I probably should have mentioned the ONH to start out. Eye doctors have told me the nystagmus is more of a symptom of optic-nerve hypoplasia, and the strabismus is likely related as well. The myopia at one time was mild, in fact I spent a few years as a kid not wearing glasses at all. Today, my perscription has gone up alot (I forgot what it actually is), but it's weaker than my parents, both of whom are myopic. My brother also finally aquired myopia a few years ago. I suspect all the eye disorders I have complicates fitting with a good perscription. > The high-minus contacts with high-plus lenses are for acquired nystagmus I suspected that too. > Interestingly enough, there are patients here and there who develop an > acquired nystagmus on top of the congenital nystagmus, and those folks > experience oscillopsia. What about drugs to control nystagmus? I have heard of experimental use of anti-convulsants, but is this for aquired nystagmus only? Years ago I took depakene (valproic acid, anticonvulsant) for an unrelated health problem. My mom commented she thought it reduced my nystagmus, but maybe her saying that was just wishful thinking on her part. In the end, a new set of optic nerves and eyes would not hurt. I have read they have used stem cells and cloning in frogs to transplant eyes into a frog and the frog could distinguish light from darkness. So who knows. I do support research on human cloning and stem cells, that's one thing I feel quite strongly about and why I did not vote for President George W. Bush (because he wants a ban on human cloning in the US, and pushing a ban on human cloning, including therepeutic uses, in the UN). I don't really hold out that kind of hope for myself but I do think it is something that should be researched because it stands to benefit all sorts of people and problems. A bunch of reactionary demagogues have no right to step in and decide it for everybody else, that's my feeling. > Hold on, I thought prisms would allow a person to read straight ahead., > to place the null point in line with the head. Why would one be required > to > look to one side? Your null point is a position of gaze. Without prism, you accomplish this by turning your head. You could hold your head straight and move the book instead, or use prism to move the image to that position for you. > Why would it be hard to adapt to walking around? Because everything you see will appear to be 15 degrees away from where it really is. It's reasonable to think you could adapt (there's a famous experiment where subjects learned to adapt wearing prism that flipped everything upside down) but it would "take some getting used to." It might be more reasonable to have two pair - prism glasses for reading and without prism for everything else. Or you might decide it's a waste of effort, if the only benefit is sitting straighter. Next time you get your eyes checked, ask the doctor to tape a couple of trial prism lenses onto your current glasses. > So they will look like "coke bottle glasses"? I might be able to live > with that. I just don't like dealing with glasses sliding down my nose > all > the time- that I'll have a harder time living with. I'm pretty sure they'd be heavier, tho maybe not much. > fingers, etc. But the congenital heart defect, epicanthic folds, and > nystagmus fit in with a number of syndromes. Yup.. nystagmus is often accompanied by other birth anomalies, including above-average IQ. :) -MT > The amount of prism needed to simulate your null point could be 50 or > 100 times the "ordinary" amount used to help binocular alignment, so [quoted text clipped - 12 lines] > > -MT Often, when a person has an eccentric null, they have a vergence null that works even better. Base-outs might be a better solution, with some added minus for the additional accomodation. Scott > How much more would a pair of glasses with prisms in them weigh? Are they > restricted to glass or certain kinds of plastic? I have never seen > prismatic glasses, and I want to learn more about them, but I'm having > trouble finding information on the web. Although not directly answering to your question, adding prism to your lenses is the equivalent of decentering for single vision glasses. That may not apply if there is little spherical correction, because the lens cannot be decentered enough. Bill > How much more would a pair of glasses with prisms in them weigh? Are they > restricted to glass or certain kinds of plastic? I have never seen > prismatic glasses, and I want to learn more about them, but I'm having > trouble finding information on the web. Hello I have had prism glasses for over 10 years now and still drive during the day. I was not able to drive for a year after having nuclear cataract surgery at age 40 to remove both natural lenses followed by 3 detached retina operations including 2 scleral buckle implants. Since I don't have natural lenses, my glasses are thicker to start with. Then when I had to have prism added to get rid of serious double vision (I saw two cars coming at me for every one in front of me). First the vision specialist Dr. Hess gave me temporary prism glasses where he stuck prism lense on the back of my regular thick glasses. This is a good way to try they out and see if you think you can adjust to them which may take a while. Then I had my first pair made of glass and they were thick and heavy but they really worked so it was worth it to me to get used to them. Since then lense making has improved and I now have a pair that is much lighter and thiner. But they are expensive to make ($300-$400 in my case) and you may want to get recommendation for optical specialist from your doctor. My prism glasses were made by Beach Optical here in St. Pete who was recommended by Dr. Hess for my special requirements. Here are links to references: http://www.healthcarenearyou.com/doctors/fl/st-petersburg-doctor.html Hess J Bruce MD 880 6th Street South St Petersburg FLORIDA 33701 727 892 4393 http://www.google.com/local?hl=en&lr=&q=beach+optical&near=St+Petersburg,+FL&oi= locald&radius=0.0&latlng=27770555,-82679444,10180187218372743084 Beach Drive Optical (727) 823-2773 238 Beach Dr NE St Petersburg, FL 33701 > I had to have prism added to get rid of serious double vision (I saw > two cars coming at me for every one in front of me). Don, Magnulus is talking about using prism for a very different purpose, in much larger amounts, to shift his position of gaze. > First the vision > specialist Dr. Hess gave me temporary prism glasses where he stuck > prism lense on the back of my regular thick glasses. Excellent suggestion. -MT >> I had to have prism added to get rid of serious double vision (I saw >> two cars coming at me for every one in front of me). [quoted text clipped - 9 lines] > >-MT These press on prisms are called Fresnel, pronounced with a silent "S". I believe they are made by 3M. Used by clinicians to determine the efficacy of prescribed prism and the only way to get significant amounts of prism in front of the eyes. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman |
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