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Medical Forum / General / Vision / October 2006Does -3 and -2.25 = -2.25?
I've been told that my prescription of -3 and -2.25 is really only the same as someone with -2.25 and -2.25 because the brain will just ignore the -3 and image and use the -2.25. Is this really true? Jane via MedKB.com schreef: > I've been told that my prescription of -3 and -2.25 is really only the same > as someone with -2.25 and -2.25 because the brain will just ignore the -3 and > image and use the -2.25. Is this really true? No. Jan (normally Dutch spoken) > I've been told that my prescription of -3 and -2.25 is really only the same > as someone with -2.25 and -2.25 because the brain will just ignore the -3 and > image and use the -2.25. Is this really true? No, not unless your brain is used to ignoring 50% of available sensory input. LB, O.D. Dear Jane, This depends completely on who you talk to. Some say "yes". Some say "no". Let us say that -0.75 diopters is equal to about 20/50 on the Snellen, and the other eye is zero diopters and 20/20. When that person reads an eye chart, the brain will form an "over-lay" of the two images and you will read (in most cases) 20/20. You can sort out the "Yes" and "No" answers to the best of your ability. Best, Otis > I've been told that my prescription of -3 and -2.25 is really only the same > as someone with -2.25 and -2.25 because the brain will just ignore the -3 and [quoted text clipped - 3 lines] > Message posted via MedKB.com > http://www.medkb.com/Uwe/Forums.aspx/vision/200610/1 > I've been told that my prescription of -3 and -2.25 is really only the > same > as someone with -2.25 and -2.25 because the brain will just ignore the -3 > and > image and use the -2.25. Is this really true? A couple have answered "no" but it isn't black-and-white. Say you wore two contacts, both -225. You'd still see road signs. You'd likely still say you "can see to drive" because you get functional distance vision with the -225 eye. In fact, a pair of -225 contacts would be my first recommendation for anyone over 40, because so many _can_ "ignore the bad eye." Do you see better with -300 and -225? Most people will say yes, but the difference isn't usually dramatic unless the -300 eye is strongly dominant. There are plenty who barely notice +0.75 blur in one eye. Likewise with astigmatism. Many people would need special toric contact lenses, except that one eye has very little astigmatism, so the other eye can tolerate a little blur from approximation with an ordinary spherical lens. The answer to your question depends on subjective perceptions, so it'll vary from person to person. Objectively, a little blur in one eye has little effect on gross stereoacuity or peripheral vision. I quit saying "the brain will ignore" but I frequently tell patients "This is the best you can get with ordinary spherical contacts. The 'bad' eye won't get better, but you will probably learn to ignore it. If you can't, it'll be worth the additional investment for a toric in the other eye." -MT, OD Mike Tyner schreef: >> I've been told that my prescription of -3 and -2.25 is really only the >> same [quoted text clipped - 9 lines] > first recommendation for anyone over 40, because so many _can_ "ignore the > bad eye." What if the original prescription is to strong ( the minus 3)? TMHO there is only one straight answer possible on this particularly question. Jan, one of the couple (normally Dutch spoken) Oh yes I see well with the -3 and -2.25 and I'm very happy with it. The comment I posted related to some *advice* that was offered to me - that as my level of defective vision was only equal to -2.25 I didn't really need to wear glasses much at all. That's really smart. So why don't you wear no glasses? How much do you see? You see the same as a myope with -3.00 and -2.25, end of story. dr grant > level of defective vision was only equal to -2.25 I didn't really need to > wear glasses much at all. That sounds like someone with an agenda, trying to convince you there is something dangerous or detrimental about wearing glasses. Most doctors don't think so. Most people with -225 wouldn't be happy watching TV without glasses. Nothing wrong with taking them off to read. -MT > Oh yes I see well with the -3 and -2.25 and I'm very happy with it. The > comment I posted related to some *advice* that was offered to me - that as my [quoted text clipped - 3 lines] > -- > Message posted via http://www.medkb.com Your unaided acuity with both eyes open would be more similar to the unaided acuity of someone with -2.25 in each eye than to that of someone with -3.00 in each eye. As to not wearing glasses, objects further away than 18 to 20 inches will be blurry without your glasses, you might be able to tolerate reading without glasses but not much else. Whether or not you "need" to wear glasses is up to you. Do you like to see clearly or not? Dr Judy > Oh yes I see well with the -3 and -2.25 and I'm very happy with it. The > comment I posted related to some *advice* that was offered to me - that as my [quoted text clipped - 3 lines] > -- > Message posted via http://www.medkb.com Your unaided acuity with both eyes open would be more similar to the unaided acuity of someone with -2.25 in each eye than to that of someone with -3.00 in each eye. As to not wearing glasses, objects further away than 18 to 20 inches will be blurry without your glasses, you might be able to tolerate reading without glasses but not much else. Whether or not you "need" to wear glasses is up to you. Do you like to see clearly or not? Dr Judy "Jane via MedKB.com" <u24939@uwe> wrote > > I've been told that my prescription of -3 and -2.25 is really only the > > same [quoted text clipped - 3 lines] > > A couple have answered "no" but it isn't black-and-white. That's true, but the poster asked if: 1 it is the same as -2.25 in both (it is not) and 2. if the brain will ignore the -3 undercorrected eye and just use the other. It will not, and depending upon whether it is the neurologically dominant eye, it might very well have a problem trying to "ignore" it. And personally, when I intentionally create an optical imbalance, I often try to "overplus" the dominant .25 and the non-dominant .75. That does indeed create a +.75 add but only a .50 differential. Almost never notice it in daylight and is often quite acceptable other times. Do that with aspheric contacts and the "wow, I can see again up close" factor is significant. LB, O.D. Dr Judy you said that my unaided acuity with both eyes open would be more similar to the unaided acuity of someone with -2.25 in each eye than to that of someone with -3.00 in each eye. Maybe that's what my friend meant when she said my vision was the same as someone with -2.25. Surely if I was unlucky enough to be -1 and -3 no-one would say my vision was like someone of -1 would they? Perhaps I'm unusual but I find it much more comfortable to wear glasses and have both eyes focused together. Dear Jane, If fact a difference of 1 to 2 diopters can be created for a person who is older that 45, and wishes to see clearly an both distance and near. It is called monovision. So if you one eye is 20/20 (and zero diopters refractive STATE), and the other eye is at 20/80 (about -2 diopters refractive STATE), you will keep your distant and near vision long after you pass the age of 50. Best, Otis > Dr Judy you said that my unaided acuity with both eyes open would be more > similar to the [quoted text clipped - 6 lines] > like someone of -1 would they? Perhaps I'm unusual but I find it much more > comfortable to wear glasses and have both eyes focused together. > It is called monovision. She didn't query anything about that. Who asked YOU to reply, anyway. Who asked you to play doctor? I take is you do not like the concept of monovision. Or do you prescribe for it? Otis > > It is called monovision. > > She didn't query anything about that. > Who asked YOU to reply, anyway. > Who asked you to play doctor? > Dr Judy you said that my unaided acuity with both eyes open would be more > similar to the [quoted text clipped - 6 lines] > like someone of -1 would they? Perhaps I'm unusual but I find it much more > comfortable to wear glasses and have both eyes focused together. I don't think you are unusual, most people would prefer to see clearly with both eyes focused together. Your friend may have been reading some websites and postings by Otis Brown (who has posted to this thread). Otis tells people with -1.50 to -2.00 that their unaided acuity isn't that bad and they should be able to get along without glasses except for driving. Feel free to correct Otis if you disagree. Dr Judy Otis tells people with -1.50 to >-2.00 that their unaided acuity isn't that bad and they should be able >to get along without glasses except for driving. > >Feel free to correct Otis if you disagree. > >Dr Judy Otis - are you an eye doctor? If you are and that's what you tell your patients I'm happy I'm not one!! Do you really believe that people who are - 2 should avoid wearing glasses except for driving? If you do, I'm curious why. > Otis - are you an eye doctor? If you are and that's what you tell your > patients I'm happy I'm not one!! Do you really believe that people who > are - > 2 should avoid wearing glasses except for driving? If you do, I'm curious > why. Otis is a layman who is substantially nearsighted, and he blames his parents and his doctors because he believes wearing glasses made it worse. Nobody will ever convince him otherwise, because he's an engineer who knows about such things. Consequently Otis has an obligation to prevent other people from abusing their children by making them wear "that wretched minus lens." He will not tell you that the FDA recently denied a petition to put warning labels on eyeglasses, because they could not verify that glasses have this effect. He will ask you to believe that a significant number of eye doctors all over the world agree with him. He will not tell you that this significant number is about ten. He believes that a vast conspiracy exists among the other hundred thousand, who defraud the public for their own advantage. -MT As always Mike gets is WRONG! I believe in science and facts. That the natural eye is a dynamic system, and will change its refractive STATE when that environment is moved closer. Here are the facts. Measurements taken from: "Visual Refractive Errors of Wild and Laboratory Monkeys" Francis A. Young Ph.D. Pullman, Washington. +++++++++++++++++++++++++++++++++++++ 1. Wild Monkeys (The control group) N = 286 eyes (of wild monkeys) had their refracitve state measured. The refracitve state (average) was +0.68. The standard deviation was 0.73 2. Inside Monkeys (The "test" group) N = 100 eyes (of inside, or caged) monkeys had their refractive state measured. The refractive state (average) as -0.36. The Standard deviation was 1.78. In statistical testing you look for confidence levels (that the natural eye is dynamic). Levels greater-than 3.9 spell virtual certainty -- that the fundamental eye is dynamic with respect to a change in its average visual environment. Here are the calculations. The large-scale statistics are: z = [ Xc - Xt ] / Sqrt [ Sigma(c) ^2 / Nc + Sigma(t) ^2 / Nt ] z = [0.68 - ( -0.36)] / Sqrt [ (0.73 ^2 / 286) + (1.78 ^2 / 100)] z = 17.0 The "Z" value for 99.8 percent confidence is 2.88. This calculated value vastly exceeds this level of confidence. Anything above 3.9 is considered a virtual certainty. Mike keeps on insisting that: 1. The eye is not a dynamic system and 2. The natural eye will not change its refractive STATE if a -3 diopter lens is placed on it. That is the majority-opinion -- with little basis in hard scientific facts --as per the above. That is why Steve Leung has his own children wearing a plus to keep their refractive STATE positive, and their distant vision clear for life -- rather than get stair-case myopia from an over-prescribed minus. There is no "conspiricy". Only the failure of Mike to recognize scientific truth concerning the dynamic beahvior of the natural LIVING eye. Otis ++++++++- > > Otis - are you an eye doctor? If you are and that's what you tell your > > patients I'm happy I'm not one!! Do you really believe that people who [quoted text clipped - 22 lines] > > -MT > I believe in science and facts. So do scientologists. Also like you, they pick and choose their facts very carefully. > That the natural eye is a dynamic system, and > will change its refractive STATE when that > environment is moved closer. What does that have to do with wearing glasses? > "Visual Refractive Errors of Wild and Laboratory Monkeys" Pretending that you can't test humans. > Mike keeps on insisting that: > > 1. The eye is not a dynamic system and False. I know the eye changes. I also know you can't manipulate it as you please. > 2. The natural eye will not change its refractive > STATE if a -3 diopter lens is placed on it. False. When you put -3 lenses on a -3 myope it does not accellerate them to -4. > That is the majority-opinion -- with little > basis in hard scientific facts --as per the above. Never mind all those measurements on real humans wearing glasses, you know, Grosvenor, Ong, Shotwell, and Parssinen. > That is why Steve Leung has his own children wearing > a plus to keep their refractive STATE positive, and > their distant vision clear for life -- rather than > get stair-case myopia from an over-prescribed minus. And I have no elephants in my yard because I bought elephant repellent from a guy on the internet. > There is no "conspiricy". Only the failure of Mike > to recognize scientific truth concerning the > dynamic beahvior of the natural LIVING eye. Like Grosvenor, Ong, Shotwell, and Parssinen. They tested actual humans and found you wrong. As if you care... -MT > That the natural eye is a dynamic system, and > will change its refractive STATE when that > environment is moved closer. What does that have to do with wearing glasses? Otis> Because of your absolute insistance that 1. The eye is not dynamic, (the Donders-Helmoltz, box-camera paradigm), and therefore 2. A -3 diotper lens has NO EFFECT ON THE REFRACTIVE STATE OF THE FUNDAMENTAL EYE. This suggests that the combination of a "nearer" enviroment results in the eye's refracitve STATE moving from a positive value to a negative value, with blur at distance, and your use of a strong minus lens as a "cure". When, in fact if the "near" enviroment were ended with a proper strength plus -- the natural eye's refractive state would remain positive. But you keep on insisting that the eye is not dynamic, the "minus" is perfectly safe, and that the minus lens does not exacerbate the situation by creating stair-case myopia. It is your lack of respect for the proven behavior of the fundamental eye -- that is the problem, and your lack of comprehension of what scientific facts actually prove about this issue -- and the consequences -- which you seek to deny. Best, Otis > > I believe in science and facts. > [quoted text clipped - 48 lines] > > -MT > Otis> Because of your absolute insistance that > > 1. The eye is not dynamic, (the Donders-Helmoltz, > box-camera paradigm), and therefore Donders-Helmholtz did not describe the eye as a box camera. Their theory is a theory of accommodation which has no relation to box cameras. > 2. A -3 diotper lens has NO EFFECT ON THE > REFRACTIVE STATE OF THE FUNDAMENTAL EYE. I think you misunderstand. No one here denies that a minus or plus lens will affect emmetropization in young eyes or accommodation in prepresbyopic eyes. You continue to insist that a -3 lens worn by a -3 myope will somehow "cause" progression of myopia and have not yet provided any scientific evidence for this. Dr Judy > This suggests that the combination of a "nearer" enviroment > results in the eye's refracitve STATE moving from > a positive value to a negative value I need more than a "suggestion". To fully appreciate your "suggestion" we must ignore Shotwell, Ong, Grosvenor, Parsinnen and several others who actually bothered to test real humans with real myopia. -MT otisbrown@pa.net schreef: > 1. The eye is not dynamic, (the Donders-Helmoltz, > box-camera paradigm) You are a liar and a charlatan Otis. Show us the evidence Donders or von Helmholtz ever stated this. What a blockhead you are Otis. Free to Marcus Porcius Cato's "Ceterum censeo Carthaginem esse delendam" In conclusion, I think the " old plus lens therapy junk recovered by Otis" should be destroyed. Jan (normally Dutch spoken) Dear Jane, No, I am not an "eye doctor". But I do support the PREVENTIVE second-opinion for children on the THRSHOLD of nearsightedness, again as the second-opinion. Read: www.chinmyopia.org for a optometrist who supports your right to an INFORMED choice in this matter of prevention. At -2 diopters (about 20/100) you are beyond the point of effective prevention. For kids at 20/60, I strongly suggest that they be informed of the PREVENTIVE second-opinion -- and THINK about this choice -- again recommended by optometrists like Steve Leung and others. Because, it is and either-or choice. Begin wearing an over-prescribed minus lens, and your kids vision will stair-case down at a rate of -1/2 diopter per year -- as documented in the scientific study conducted by Dr. Oakely (MD) and Dr. Young. So I suggest "care" about this issue with children on the threshold. Best, Otis > Otis tells people with -1.50 to > >-2.00 that their unaided acuity isn't that bad and they should be able [quoted text clipped - 11 lines] > Message posted via MedKB.com > http://www.medkb.com/Uwe/Forums.aspx/vision/200610/1 Otis I’ve never heard about this theory in any real detail before. I can understand a need to be careful with young children’s health – not only their eyesight – but for me that's only one aspect of the debate. Do you believe that adults who, like me apparently, are “beyond the point of effective prevention” should also avoid wearing glasses? You describe me as -2 which I am close to in one eye, but in the other – which is off the chart in an eyetest – I consider I have very poor vision. Would you really advocate that I just try and get now by so that my eyesight doesn’t get worse? If yes, when do you think that it does become acceptable for someone to wear glasses for more than just driving a car? > Otis > I’ve never heard about this theory in any real detail before. Jane, Please disregard Otis's postings. He is not in the medical profession nor in any position to give medical advice. Thanks! Allen Dear Jane, I support the concept that the fundamental eye is a dynamic system -- by direct scientific testing. In other words, if you take a population of young eyes, and place a -3 diopter lens on 1/2 of them, the -3 diopter group will change their refracitve STATE by greater-than -2 diopters in about 120 days. This scientific truth is denied by the majority-opinion and affirmed by the second-opinion. I support the concept that you be informed accurately of these facts BEFORE you are put into a strong minus lens. I do agree that this is indeed a difficult choice -- but you should have the scientific facts presented to you, before your Snellen goes much below 20/40. I would also agree that kids INDUCE a negative refractive STATE in their natural eyes -- by the same means that the primates can have a negative refractive STATE induced in THEIR EYES. It is a natural process. But plus-prevention is indeed difficult as I freely acknowledge. But it is an honest choce, where "neglect" is not a good idea. To furhter respond: Otis I've never heard about this theory in any real detail before. Otis> Understandable. I can understand a need to be careful with young children's health - not only their eyesight - but for me that's only one aspect of the debate. Otis> Again -- true enough. Do you believe that adults who, like me apparently, are "beyond the point of effective prevention" should also avoid wearing glasses? Otis> I believe that you should use a minus only when absolutly necessary -- i.e., to drive a car -- or at the movies. I suspect your Snellen would be about 20/60 to 20/70 at this point -- but you should check this youself. You describe me as -2 which I am close to in one eye, but in the other - which is off the chart in an eyetest - I consider I have very poor vision. Otis> A number of the DMV tests are written for both eyes open. You would then pass those DMV tests -- assuming you read their standard. The Florida calls for 20/70 or better. Georgia for 20/60 or better. Would you really advocate that I just try and get now by so that my eyesight doesn't get worse? Otis> If it were me -- and I could pass the 20/70 line? If that were the case, then I would not wear the minus unless driving a car. It is a matter for your judgment. Just be legal at all times. If yes, when do you think that it does become acceptable for someone to wear glasses for more than just driving a car? Otis> That MUST be a matter of your judgment. I look at the effect of a -3 diopter lens on the natural eye -- and see that eye change by -2 diotpers in 120 days. In my judgment, the minus is understandabley and easy "default" lens -- but with a child at 20/50 to 20/60, I would suggest a review of the preventive second-opinion -- and described and supported by second-opinion optometrists. Clearly your child would have nothing to lose for a DISCUSSION of that nature. I certainly would have liked to be so informed when I was at 20/50. There would also have been a NECESSARY review of my "habits" in reading -- and that is a critical issue. (You can read -- but you must do it through a +2 diopter lens -- assuming 20/60 on the Snellen). There are optometrists who have recognized these issues. It is important that we understand them -- but that it is critical that you have this understanding. Best, Otis > Otis > I've never heard about this theory in any real detail before. I can [quoted text clipped - 8 lines] > when do you think that it does become acceptable for someone to wear glasses > for more than just driving a car? > Dear Jane, > [quoted text clipped - 5 lines] > in about 120 days. This scientific truth is denied > by the majority-opinion and affirmed by the second-opinion. Would you stop the bullshit already. Just show us one peer-reviewed study that even comes close to that "result". Of course you cannot. It's simply untrue, false, a lie. Stop making stuff up. > I support the concept that the fundamental eye is a dynamic > system -- by direct scientific testing. In other words, if > you take a population of young eyes, and place a -3 diopter > lens on 1/2 of them, the -3 diopter group will change > their refracitve STATE by greater-than -2 diopters > in about 120 days. That's patently absurd. It doesn't happen, and you look foolish trying to pretend it does. -MT > Otis > I've never heard about this theory in any real detail before. I can > understand a need to be careful with young children's health - not only their > eyesight - but for me that's only one aspect of the debate. Otis has his own opinion of what causes myopia and how to prevent/reverse it. No scientific studies support his ideas (he will quote some animal studies but they are not relevant) most have actually shown that his suggested method is ineffective and some have actually found that not wearing full correction will INCREASE myopia progression. Best to ignore him Dr Judy Very strange and not always true. I wasn't myopic when I was a child. In fact I wasn't till my late 20s. When I got glasses I had a low prescription for a long time that I did just wear for driving. It was only beyond -2 that I ever felt I really benefited from them so I'd hardly say that they made my eyesight worse. I'm more likely to believe it's the fact that we all have our noses pressed against computer screens that does it. The 20/50 or 20/70 doesn't mean much to me and yes the test is also done with both eyes open, that doesn't disregard in real life that one eye is -2.25 and the other is more than that with very poor vision. For the eye professionals here, do you have other patients similar to me and do they feel the same? > Very strange and not always true. I wasn't myopic when I was a child. In > fact [quoted text clipped - 4 lines] > felt I really benefited from them so I'd hardly say that they made my > eyesight worse. Nor can we, when we compare groups of children wearing glasses with groups of children who don't. If the Otis theory had any validity, there'd be a glaring difference in the rate and amount of myopia between these two groups. In the six or seven major studies I've found that did this, there was no significant difference. > I'm more likely to believe it's the fact that we all have our > noses pressed against computer screens that does it. The literature DOES support this contention. Myopia is positively correlated with short working distances and length of time spent in near work. Lenses don't appear to matter. > For the eye professionals here, do you have other patients similar to me > and > do they feel the same? Yes. Your myopia started somewhat late but otherwise follows a typical S-shaped curve, increasing to a point then levelling off. Very few are born nearsighted. -MT |
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