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Medical Forum / General / Vision / July 2004Flitcroft paper on "stair-case" change in refractive status
To: Friends From: Otis Brown Subject: Vision paper on myopia "staircase" effect. Here is the paper that shows the "stair-case" response Of the natural eye to: 1. A confined visual environment. 2. The effect of a series of increasingly stronger minus lenses, to match the "induced" negative refractive status. 3. The result is that the "step input" is the minus lens, and the response is exponetial (e ^ -t/Tau) "cusps", which is the response you would expect from an automatically focused camera that gains its "input" from the accommodation SIGNAL. Best, Otis ***** Pergamon -- Vision Research Vision Research 38 (1998) 2869-2879 Flitcroft Vision A model of the contribution of oculomotor and optical factors to emmetropization and myopia. D. I. Flitcroft Institute of Ophthalmology, University College Dublin 60 Eccles Street, Dublin 7, Ireland Received in revised form 15 December 15, 1997 Abstract: The purpose of this work was to investigate quantitatively the interactions between accommodation, vengeance and a mechanism of emmetropization driven by optical blur within the retinal image with a view to developing a model that provides an explanation of both normal emmetropization and near-work associated myopia. The simulations of the change in the refractive state of the eye over time that derive from this model indicate that optical regulation of eye-growth can result in emmetropization, i.e., a progressive reduction in refractive errors over time leading towards emmetropia. This occurs when viewing conditions involve a preponderance of distance work. With increasing near work, the model predicts that the refraction of the eye will converge towards myopia. In keeping with the previously reported associations of myopia with esophoria, poor accommodation function and high AC/A ratios, these conditions increase the amount of myopia produced under intensive near viewing conditions but do not lead to myopia during mainly distance viewing. The model provides quantitative validation of the hypothesis that the epidemiological association between myopia and increased near-work may be caused by a disturbance of normal emmetropization by steady state errors of accommodation. The same model can explain normal emmetropization, increasing myopia with increasing near-work demands and the currently recognized oculomotor associations that have been reported to precede the development of myopia. Elsevier Science Ltd. Keywords Accommodation, Vengeance; Myopia; Emmetropization ___________ The paper is covers 11 pages. I received it from Dr. Dave Guyton at JHU. _____________ Figure 9 Graph showing the change in refractive (vertical axis) over repeated interactions (horizontal axis) from a starting refraction of +2 D with other parameters as for Fig 4a. The dotted line shows the change in refraction without spectacle correction and the dashed line shows the effect of progressive correction of the induced myopia (spectacle correction shown as solid line). Figure 10 Graph showing the change in refraction (vertical axis) from a starting refraction of +2 D with other parameters as for Fig. 4a. The dashed line shows the change in refraction with a -0.5 D correction from iteration 20. The dotted line shows the effect of a -0.5 D distance correction with a +1.5 near addition. I'm glad that Otis brings up Flitcroft. You will also notice that he selectively quotes from a paper published in 1997. I would now like to quote from a paper published in 2004, by RA Stone and DI Flitcroft, entitled Ocular Shape and Myopia (Ann. Acad. Med. Singapore, vol. 33): "The insight that normal refractive development is regulated by visual quality has diminished the likelihood that accommodation comprises a primary mechanism for the cause of myopia... Bifocal and varifocal lens treatments, at least with protocols adapted to date, have either revealed NO reduction of myopia progression OR a stasticially significant reduction that is too small in magnitude for clinical import." You see, friends, even Flitcroft recognizes that new scientific information requires a re-adjustment in one's thinking. DrG > To: Friends > [quoted text clipped - 97 lines] > correction from iteration 20. The dotted line shows the effect of > a -0.5 D distance correction with a +1.5 near addition. > I'm glad that Otis brings up Flitcroft. You will also notice that he > selectively quotes from a paper published in 1997. [quoted text clipped - 14 lines] > > DrG Excellent! That is one helluva "got you" there! You see, folks, the difference between SCIENTIST and ZEALOT is indeed clear. Otis, now matter how many times he is shown *science* will retort with the typical "zealot response": "stop confusing the issue with the facts! I know what it true because I understand the *true* workings of the system." And then: "There's a conspiracy to support the wrong conclusions." And then: selectively chosen, often ancient (but since adjusted/corrected) reprints, often out of context, in the continuing struggle to support unsupportable claims. The definition of a zealot. Go, Otis. Go. Show us more BS. Or better still, just go away. --LB Wow! I hadn't realized Otis was advocating bifocal and varifocal lens treatments to restore unaided distance acuity. Thanks for the clarification! I assume by your quoting Flitcroft's 2004 article that you believe "normal refractive development is regulated by visual quality". I didn't get further than the abstract on PubMed, so I will trust your presentation is from the body of the article and is not out of context. So, what is providing the visual quality? From further in your quote, it would seem to be bifocals. Therefore, the bifocals are regulating normal refractive development. The outcome of "NO reduction of myopia progression" should have been predicted precisely because of the control taken by the bifocals for distance viewing, near work not being the issue in myopia. A second point I note is that visual quality is suspected, by insight, to push accommodation out of first place as a "mechanism for the cause of myopia". Leaving it, potentially, as a secondary mechanism? The "new scientific information" described in the abstract was that RA Stone and DI Flitcroft are interested in "incorporating the 3-dimensional conformation of the eye into future clinical studies". They gave no hint that they've changed their minds about their 1997 conclusions. Is the abstract off-base as to the thrust of the paper? Your reply will help me decide the usefulness of PubMed. Thanks, Cathy > I'm glad that Otis brings up Flitcroft. You will also notice that he > selectively quotes from a paper published in 1997. [quoted text clipped - 116 lines] > > correction from iteration 20. The dotted line shows the effect of > > a -0.5 D distance correction with a +1.5 near addition. > Wow! I hadn't realized Otis was advocating bifocal and varifocal lens > treatments to restore unaided distance acuity. Thanks for the [quoted text clipped - 147 lines] >> > correction from iteration 20. The dotted line shows the effect of >> > a -0.5 D distance correction with a +1.5 near addition. I quoted from the text of the full article. And, yes, Otis is (in)famous for promoting plus lenses for the prevention of myopia, and often quotes studies involving progressive lenses, accommodation, minus lens-induced myopia in order to promote his theories. As to the rest of your questions, I will deflect the intellectual energy for answering them back into your court. DrG > I quoted from the text of the full article. And, yes, Otis is (in)famous > for promoting plus lenses for the prevention of myopia, Bifocals for myopes are not plus lenses. They are minus for distance and less minus for near work. -4.00 +1.75 = -2.25, a net minus. One can't credibly say plus lenses don't work when the studies that have been cited used less minus. and often quotes > studies involving progressive lenses, accommodation, minus lens-induced > myopia in order to promote his theories. As does Flitcroft. > As to the rest of your questions, I will deflect the intellectual energy > for answering them back into your court. > > DrG > > I quoted from the text of the full article. And, yes, Otis is (in)famous > > for promoting plus lenses for the prevention of myopia, [quoted text clipped - 3 lines] > credibly say plus lenses don't work when the studies that have been cited > used less minus. Cathy I have sometimes worn plus lenses over the top of my distance minus lenses to do prolonged periods of close work. This kind of plus lens use was advocated by James Arthur http://members.aol.com/myopiaprev/improvin.htm who for years was trying to remove his myopia. He finally concluded that beyond a 1.5D improvement he was never going to get more improvement. So must of us would consider varifocal lenses to be plus lens therapy. However this is all a distraction for me, I dont believe that myopia has got much at all to do with glasses. You began your posts to Dr Leukoma with an apparently triumphant celibration that finally you could now understand what Otis was talking about. As wacky as it might seem, I believe that this kind of indirect communication is related to being myopic. In myopia there can be a tendency to publicly be a wee bit aggressive towards others, while actually privately being rather timid or shy. Visually, in myopia, our focus of attention is close to ourselves. Myopia seems to arise after stressful experiences in our lives, often happening at times in our lives when we are vulnerable and have little control or power to change things around us. Rather than the environment changing, we changed. Unfortunately to improve myopia it is not the visual environment that now has to change! :-( Andrew > Unfortunately to improve myopia it is not the visual environment that > now has to change! All imperfect sight is improved by rest, temporarily in a few minutes, permanently by continued treatment. However, the significance and action you give to the word "rest" may prove to be quite unsatisfactory. Same with the word "strain". It requires a good and open mind to understand experientially these words. Those who do not understand them won't do any progress in their treatment. Apart from understanding of these two words, rest and strain, indeed a good visual environment is needed to make use of the two words and practice accordingly. As the little boy who is building a castle of cards, he needs not to be disturbed by the wind, otherwise the cards will easily fall down. Instead, if the boy is protected from the wind and completes his castle, then the wind won't do any harm because even if the castle falls down, he had accomplished his own cure from it and won't suffer anymore. Children under treatment of imperfect sight by means of rest methods do suffer very much the strain that comes from people of his own family who have imperfect sight and may not be strong enough to complete their castle before some raft of wind tears it down again and again. Any time the castle falls down, the boy will have to start again from scratch and even if he will be more skillful, and quick, he loses much time and the process of completing the castle is prolonged. If the boy has not clear in his mind that the complete castle has to be built, he won't build it for ever. If you imagine the subtlety of the final act of placing the right card in the right place at last and have the castle completed, perhaps you may have a little glimpse of what the treatment of imperfect sight by means of rest methods is. The last card is fragile. It requires the boy a great silence of mind when he places it. This silence cannot be accomplished by effort or strain. It has to be simply revealed by the very core of his being, which is not-tense by definition. Only the inherited mind of the boy is tense and disturbed by any sort of repressive education, longings and false goals. His original mind is unpolluted, but covered with mud. Those who are advanced in their own cure of imperfect sight, namely those who have gained a certain degree of relaxation as to be able to gaze at mid-day sun or to demonstrate normal vision in favourable conditions and are able to avoid suffering under unfavourable conditions, can help beginners by encourage them with the practice and showing that the total mass of wrong things that old and modern eye-science is pushing forward is not only dangerous but mischievous and criminal. We should not be concerned of these people anymore. We should be safe with our own contention about the high value of central fixation so as to discard with great suppleness the totality of the accepted ideas about vision, both from the scientific-medical paradigms and from the alternative-faith-healers freaks. > Bifocals for myopes are not plus lenses. They are minus for distance and > less minus for near work. -4.00 +1.75 = -2.25, a net minus. One can't > credibly say plus lenses don't work when the studies that have been cited > used less minus. If you want to alter each individual's vision by 3D of "plus" then you could only give "plus" lenses to myopes of -275 and less. Putting +300 lenses on a -300 myope nets you +600 D of blur, roughly double the blur and twice as debilitating. The purpose is to eliminate accommodation and even to induce a little myopic blur in order to stop the eye from accommodating, because accommodation causes myopia. It doesn't, but to apply "plus" equally to people of different refractive states, we have to measure "plus" relative to the each individual. It can't be that the eye knows what shape of lens produced the blur. -MT > If you want to alter each individual's vision by 3D of "plus" then you could > only give "plus" lenses to myopes of -275 and less. Putting +300 lenses on [quoted text clipped - 9 lines] > > -MT Hi Mike, What might be the likely Bifocal Rx for a -600 myope? Fran > What might be the likely Bifocal Rx for a -600 myope? Leung found a dose-dependent effect, so if we accept his findings (and ignore all the others) we'd use stronger adds, like +200 or +250. -MT >> What might be the likely Bifocal Rx for a -600 myope? > > Leung found a dose-dependent effect, so if we accept his findings (and > ignore all the others) we'd use stronger adds, like +200 or +250. > > -MT Mike, I'm not being facetious. I really would like to know what YOU would prescribe for a myopia of this degree, excluding the possibility of astigmatism, etc. Cheers, Fran > Mike, I'm not being facetious. I really would like to know what YOU would > prescribe for a myopia of this degree, excluding the possibility of > astigmatism, etc. If I were a true believer, for a -600 myope I'd prescribe -550 with a +200 add. -MT Francine, In case this post wasn't merely a test of Mike's forthrightness, he gave this answer in the lens/distance thread: "One over distance in meters". Cathy > > Mike, I'm not being facetious. I really would like to know what YOU would > > prescribe for a myopia of this degree, excluding the possibility of [quoted text clipped - 4 lines] > > -MT Sorry, I should have continued ... From there it's just math. Without glasses, a -6.00 myope can focus at approximately 6.5". 1/(6.5/39.4) = 6.00. At what distance does your myope want to focus through the weaker part of his bifocals? Plug in your number for the net minus needed required for that distance. If 14.25", 1/(14.25/39.4) = 2.75. To get from -6.00 to -2.75 you add 3.25. Any weaker than a net -2.75, and your -6.00 myope will be able to see farther through the weaker part of the bifocals, but will be accommodating more (possibly an imprecise term) to focus at 14.25". Of course, when he can't see anything farther than 14.25" through the -2.75 part, he'll use the -6.00 part and accommodate as necessary at the intermediate distances. Cathy > Francine, > [quoted text clipped - 12 lines] > > > > -MT > > Bifocals for myopes are not plus lenses. They are minus for distance and > > less minus for near work. -4.00 +1.75 = -2.25, a net minus. One can't [quoted text clipped - 5 lines] > a -300 myope nets you +600 D of blur, roughly double the blur and twice as > debilitating. Twice the blur at 20 feet and none at 13 inches. > The purpose is to eliminate accommodation and even to induce a little myopic > blur in order to stop the eye from accommodating, because accommodation > causes myopia. It doesn't, But accommodation is associated with myopia. Less minus doesn't break the association. Zero or plus does. but to apply "plus" equally to people of > different refractive states, we have to measure "plus" relative to the each > individual. It can't be that the eye knows what shape of lens produced the > blur. > > -MT > But accommodation is associated with myopia. Less minus doesn't break > the association. Zero or plus does. Accommodation is associated with close work. The purpose of posting references to Flitcroft and others was to show how the association between accommodation and myopia may not be as significant as once thought. DrG Not as significant as the "primary mechanism for the cause of myopia" because they're thinking image quality regulates eye size and shape which, I humbly submit, the lens has to accommodate for at all distances. Does that work? Not being the cause doesn't eliminate it as big trouble. Don't worry, I'm reading through the magazine. I don't want to miss anything. Cathy > > But accommodation is associated with myopia. Less minus doesn't break > > the association. Zero or plus does. [quoted text clipped - 4 lines] > > DrG > Not as significant as the "primary mechanism for the cause of myopia" > because they're thinking image quality regulates eye size and shape [quoted text clipped - 6 lines] > > Cathy I suspect you are lost in the maze of imprecise knowledge and imprecise definitions. Please keep reading. DrG >> Not as significant as the "primary mechanism for the cause of myopia" >> because they're thinking image quality regulates eye size and shape [quoted text clipped - 11 lines] > > DrG From my reading it appears that accommodative infacility may be more of a factor in the etiology of myopia than EXCESSIVE accommodation, which is what many people believe. And once the eyeball has lengthened appreciably, does one need to accommodate at all? I know myopes who do very poorly on convergence and accommodation tests, yet they can see very small print up close. I am semi-educated on this subject; am I off-base here? Fran > From my reading it appears that accommodative infacility may be more > of a factor in the etiology of myopia than EXCESSIVE accommodation, [quoted text clipped - 5 lines] > > Fran Most studies cite greater myopic progression in children with greater lag of accommodation, which is associated with higher AC/A ratio, and greater convergence - i.e. esophoria. The COMET study reported a small, but significant effect of progressive addition lenses in these patients. It is as though in order to maintain single binocular vision, the patient has to give up accommodation, which leads to increased retinal blur. However, as the Stone/Flitcroft paper says, there are other causes of retinal blur, such as spherical aberration and coma, which are due to the shape factor of the eye. This could be one reason why plus lenses are only minimally effective at best. DrG > Most studies cite greater myopic progression in children with greater lag > of accommodation, which is associated with higher AC/A ratio, and greater > convergence - i.e. esophoria. Dr Leukoma Can you explain the above passage. I am not trying to be funny here. When you say lag are you talking about the accommodation hysteresis or lag or delay between change of accommodation and final accommodation? When you say AC/A ratio you are meaning accommodation to convergence ratio right? but you say greater convergence? Not sure exactly what you mean here. I mention this because what you seem to be saying does describe a pattern that seems to be relevant to my own vision Andrew >> Most studies cite greater myopic progression in children with greater >> lag of accommodation, which is associated with higher AC/A ratio, and [quoted text clipped - 16 lines] > > Andrew By lag, I mean how far behind the plane of regard is the accommodative focus. A high AC/A ratio means that there is more convergence per unit of accommodation. The theory is that the preference for single binocular vision takes precedence over a slightly blurred image. DrG ... where I found you. I'll take this as a cordial "Welcome to my world." and politely reply, "Thank you." ;) Cathy > I suspect you are lost in the maze of imprecise knowledge and imprecise > definitions. Please keep reading. > > DrG > ... where I found you. I'll take this as a cordial "Welcome to my > world." and politely reply, "Thank you." ;) [quoted text clipped - 5 lines] >> >> DrG Er, well, not exactly what I meant. What I meant was that I had difficulty following your reasoning. I did not conclude that you were too confused to help, but that you were not receptive to any explanations from me, and so I suggested that you continue on your journey of self-help until it all made sense. DrG > But accommodation is associated with myopia. Less minus doesn't break the > association. Zero or plus does. The association is with working distance and time spent at near, not exactly accommodation. Papers I've read say that relieving accommodation with plus doesn't change the outcome of myopia. A -300 D myope "relieves" 3D of accommodation when he takes his glasses off to read. A -100 myope must wear +200 lenses to "relieve" 3D of accommodation. A -600 D myope must wear -300. The eye can't know the shape of the lens, only the blur. Too much blur is a bad thing. They can't function and we know excessive blur stimulates myopia in the very young. Working at 13" makes myopia worse, but relieving accommodation hasn't a good track record for changing that. -MT > > > Bifocals for myopes are not plus lenses. They are minus for distance > and [quoted text clipped - 18 lines] > But accommodation is associated with myopia. Less minus doesn't break the > association. Zero or plus does. I don't think you understand accommodation or plus lenses. A 6D myope using -3.00 at near, has exactly the same accommodative demand as non myope using +3.00 to read. A 6D myope using a zero power lens to read will need to hold the reading material no further away than about 6" to see it clearly, and will use accomodation only if reading closer than about 6". If you were to force plus on the poor myope, then he would have to hold it even closer to see it clearly, at great strain to the convergence system. A non myope using +3.00 will need to hold reading material no further away than about 14" to see it clearly and will use accommodation only if reading closer than 14". Dr Judy > but to apply "plus" equally to people of > > different refractive states, we have to measure "plus" relative to the [quoted text clipped - 3 lines] > > > > -MT > I don't think you understand accommodation or plus lenses. A 6D myope > using -3.00 at near, has exactly the same accommodative demand as non myope > using +3.00 to read. And yet, myopia progression is not significantly slowed when the 6D myope uses -3.00 at near. At the same time the non myope's +3.00 doesn't progress toward myopia. If the time spent at near work, implying accommodation, is the same for these two, the progression down the myopia scale should be the same, recognizing that they both began as hyperopes. We're not talking about the causes of myopia, but management. The articles referred by Mike Tyner and Dr. Leukoma in the last couple of weeks, while not making eureka claims, have suggested a different response between a relative plus and actual plus is to be expected, whether or not the wearer can focus on what he's looking at. The amount of time an acual plus might have to be used in order to undo the progression a relative plus allows in a day shouldn't interfere too much in one's lifestyle. Your explanation below speaks to convergence comfort while reading. I have no argument on that point. Thank you for your response. Each one of you professionls on this newsgroup bring up a different point or aspect. I admit to not understanding all the nooks and crannies of accommodation or plus lenses. The comment you're answering was offered by Dr. Tyner in a previous thread regarding spasm. Here we're focused mainly on eye size. The information in the referred articles relate to eye size, so I stand by the distinction between relative plus and actual plus for this thread. That is, until you guys throw me another "you didn't incorporate this". Cathy > A 6D myope using a zero power lens to read will need to hold the reading > material no further away than about 6" to see it clearly, and will use [quoted text clipped - 5 lines] > > Dr Judy > And yet, myopia progression is not significantly slowed when the 6D > myope uses -3.00 at near. At the same time the non myope's +3.00 [quoted text clipped - 9 lines] > order to undo the progression a relative plus allows in a day > shouldn't interfere too much in one's lifestyle. It looks to me like you are trying to bend the facts to fit your preconceptions. A non-myope can be a hyperope or an emmetrope. Assume in this case that the non-myope is an emmetrope and a presbyope. By definition, the presbyope is older and is no longer in the sensitive period for the development of myopia. Furthermore, if one is to generalize from the animal research, the non-myope emmetrope would need to wear the +3.00 prescription nearly full-time, and never remove it, and even then - because of reasons not yet fully understood - may never become myopic, especially if they are adults. As has already been mentioned, not all +3.00 hyperopes become emmetropic, either, even if they do not wear correction. These people accommodate all the time. DrG The fallacy of speculating how "all eyes" behave is really rather obvious, if one uses simple observation. I was a jeweler for 30 years, and most of us wore plus lenses when we had to see something really, really small, and we needed to resolve distances of 1/20 of a millimeter. No one's vision got closer to emmetropia by doing this. Some of us, like me, did start out as emmetropes. Some people's eyes hurt all the time from the close work, and they kept eyedrops on their benches close at hand. Some people's eyes hurt from wearing +350 optivisors with prisms in them, and so they did not wear the optivisors. The quality of their work suffered as a result. Some people, like me, could wear the optivisor all day and adjust instantly to any focal distance once I took them off. I know that I was just lucky; I wasn't at that time doing anything differently from anyone else in my profession. My point is: We were all doing the same kind of work, and we all had somewhat different capacities at the start, and wearing these "strong plus" had no emmetropization effect. Some of us developed eyestrain, others presbyopia, as time wore on. Like the rest of the population, we were all very different. Most of us, BTW, started out as jewelers when we were teenagers, or even younger. Fran ```````````` >> And yet, myopia progression is not significantly slowed when the 6D >> myope uses -3.00 at near. At the same time the non myope's +3.00 [quoted text clipped - 25 lines] > > DrG > The fallacy of speculating how "all eyes" behave is really rather > obvious, if one uses simple observation. [quoted text clipped - 52 lines] >> >> DrG The same reasoning applies to thinking that all eyes of a given refractive power focus the light the same way. We are trying to use antiquated classical optical theory to understand a complex optical problem. DrG > The same reasoning applies to thinking that all eyes of a given refractive > power focus the light the same way. We are trying to use antiquated > classical optical theory to understand a complex optical problem. > > DrG Yes, that is what I am trying to say in my own way. Individuals and eyes respond in their own individual manner. Fran Major snip......... > The same reasoning applies to thinking that all eyes of a given refractive > power focus the light the same way. We are trying to use antiquated > classical optical theory to understand a complex optical problem. > > DrG Can you explain the phrase ''antiquated classical optical theory'' and especially the word ''antiquated'' May I mention a myopic (not presbyopic) having an error in refraction of + 6 diopters and wearing glasses instead of contactlenses has the comfort of getting 3dpt by only 2,5 dpt real accommodation? What about the convergence comfort for the high myopics wearing glasses? Certainly classical optical knowledge but not outdated and still handy to keep in mind when fitting contactlenses. I think the problems you are trying to explain are not only optical and indeed more complex. Jan (normally Dutch spoken) > Major snip......... > [quoted text clipped - 17 lines] > > Jan (normally Dutch spoken) I mean "antiquated" in the relative sense of understanding things like spherical aberration, coma, prolate, and oblate as they impact the focus of an image on the retina. The last time I refracted somebody(today), I measured only sphere and cylinder, and I prescribed only sphere and cylinder. Let me throw out other terms like "prolate" and "oblate." I believe that the Stone-Flitcroft paper explains this better than I can. DrG > > And yet, myopia progression is not significantly slowed when the 6D > > myope uses -3.00 at near. At the same time the non myope's +3.00 [quoted text clipped - 25 lines] > > DrG At least you're still talking to me. I'm a bit surprised, but pleased. About the facts: Dr Judy's post was about which lens is required for an equal accommodation demand at 14". Your post seems to be about equal blur at distance, that the blur at distance is supposed to be, but isn't, a trigger toward myopia. In any event, our facts all match. We three recognize that +3D more than corrected (net -3D for myopes, net +3D for emmetropes, and I assume a net +6D for hyperopes) gives all a reading distance of about 14" without accommodating (if I interpret Dr Judy's meaning correctly) and that only the myope, the net minus, is likely to progress further minus. What I have read in the abstracts and articles is that minus lenses (not the +3.00 prescription you refer to in your emmetrope example) were placed on non-myopes who quickly became myopes. Then the fun began of trying to find the key to undoing the myopia. Removing the lenses didn't stop the progression; using plus lenses did. Using strong plus lenses reversed it. Again, no eureka claims, but against conventional wisdom. Or is it? A runaway truck driver might rather have a ramp where the elevation change is actually a sharp plus than one that merely reduces its descent or levels off. Cathy > What I have read in the abstracts and articles is that minus lenses > (not the +3.00 prescription you refer to in your emmetrope example) [quoted text clipped - 7 lines] > > Cathy I am missing the part where -3 lenses were placed on non-myopes. Are you referring to animal studies? The facts are that myopic progression occurs with or without the use of lenses. My experience is that myopia tends to increase in childhood, whether minus lenses are prescribed or not. One recent study showed that myopes who did not wear their minus lenses got more myopic than the group who did. Here's another way to think of it. You are a child with a -2.00 prescription. In other words, the power of your eye is +2.00, which requires a lens of equal but opposite sign to neutralize. I present you with several choices. The first choice is to do nothing, in which case your far point is 50 cm. The second choice is to wear -2.00 lenses full- time. Your far point is then infinity, and you have to accommodate more to read. The third choice is to provide bifocals with -2.00 in the top, and a +2.00 addition for reading. The +2 cancels the -2, and so the net effect is no lens power for near, and you are therefore back to a far point of 50 cm. Optically speaking, the first and third choices should be equivalent for reading. However, overall, you would experience more blur more of the time if you wore nothing. What would be the point of wearing +2.00 spectacles? DrG > > What I have read in the abstracts and articles is that minus lenses > > (not the +3.00 prescription you refer to in your emmetrope example) [quoted text clipped - 7 lines] > > > > Cathy > I am missing the part where -3 lenses were placed on non-myopes. Are you > referring to animal studies? Yes, and they were -15 lenses. The article was published in Investigation Ophthalmology & Visual Science. 2003;44:2818-2827, titled "Potency of Myopic Defocus in Spectacle Lens Compensation", by Ziaoying Zhu, Jonathan A. Winawer, and Josh Wallman. The articles you led me to are, of course, Stone/Flitcroft's "Ocular Shape and Myopia" (Ann. Acad. Med. Singapore, vol. 33) and in the same publication, "Using Natural STOP Growth Signals to Prevent Excessive Axial Elongation and the Development of Myopia" by J. Morgan and P. Megaw. > The facts are that myopic progression occurs with or without the use of > lenses. My experience is that myopia tends to increase in childhood, > whether minus lenses are prescribed or not. One recent study showed that > myopes who did not wear their minus lenses got more myopic than the group > who did. I remember reading that, and the facts you state are substantiated in the referred papers. The distinction is plus, not 0, for successfully stopping progression. > Here's another way to think of it. You are a child with a -2.00 > prescription. In other words, the power of your eye is +2.00, which [quoted text clipped - 11 lines] > > DrG Consistent with the articles by Zhu et al, Stone/Flitcroft, and Morgan/Megaw, the point of a myope wearing +2.00 is to stop or reverse myopia. (I don't say +2.00 as a prescription, only as a response to the thought conveyed in your last question.) Your three choices, on the other hand, are a menu for myopic progression. Whether or not this idea of plus lens therapy will eventually be found to work in humans, my only point throughout has been that less minus is not plus, so the outcomes of each (less minus vs. plus) can't be expected to be equivalent. Cathy > Consistent with the articles by Zhu et al, Stone/Flitcroft, and > Morgan/Megaw, the point of a myope wearing +2.00 is to stop or reverse [quoted text clipped - 8 lines] > > Cathy Consistent with the work of Morgan/Megaw, and others, with chickens, who state the effect of a high plus lens which far exceeds the natural myopic defocus of the chick eye for brief intervals. The key here is inducing a greater myopic defocus than the natural optics of the eye, and whether it works on humans. I eagerly await the results of such an experiment. DrG > Consistent with the work of Morgan/Megaw, and others, with chickens, who > state the effect of a high plus lens which far exceeds the natural myopic > defocus of the chick eye for brief intervals. Neat, huh? I haven't lost you because it's with chickens, have I? Chicken eye shape is predictably modified by altering visual input with the resulting eye shapes seeming to match human eye shapes. The response of chicken eyes to the removal of negative lenses is similar to that experienced by human myopes in that the burst of myopic defocus fails to prevent continued excessive axial elongation. So far, so good. > The key here is inducing a greater myopic defocus than the natural optics > of the eye, and whether it works on humans. I eagerly await the results of > such an experiment. > > DrG I haven't lost you because experiments have yet to be done on humans, have I? The math won't change. Using the formula 1/distance in meters, all distances require a negative lens to neutralize, even if you can see 1000 feet. Greater myopic defocus than the natural optics of the eye can be achieved only with a plus lens. If you know, what's the scientific support for poo-pooing chicken studies? Seems they're on the right track since they can induce, then uninduce, our different situations at will. Or is it just principle, that chickens aren't humans? Until now, I had no good reason to prefer to be a chick. Oops, I haven't lost you because of the cheep joke, have I? Cathy Sorry, but I got lost in your translation about accommodation. > If you know, what's the scientific support for poo-pooing chicken > studies? Seems they're on the right track since they can induce, then > uninduce, our different situations at will. Or is it just principle, > that chickens aren't humans? The scientific support for poo-pooing chicken studies is in the Morgan/Megaw bibliography pertaining to primate studies(you should have known). > Until now, I had no good reason to prefer to be a chick. Oops, I > haven't lost you because of the cheep joke, have I? I love chickens, especially on the Bar-B-Que. DrG > Sorry, but I got lost in your translation about accommodation. > > [quoted text clipped - 13 lines] > > DrG Ow! The chick has been skewered by the monkey! (I mean that study-wise, of course.) Now for some intellectual energy ... Let's see ... Morgan/Megaw sabotage their work with their own bibliography. I didn't know. I thought M/M were very generous to allow that attempts had been made in the 2003 monkey reference to use STOP signals. Maybe they were attempting to find one. The method that failed was the removal of lenses, not the placement of plus lenses. Those results can't be a surprise. Do the same test; get the same answers. Is that the reference you meant as invalidating chicken studies? The 1995 studies (too old for consideration?) are summarized by M/M as providing evidence that GO and STOP signals, similar to what they'd been working on, are present in non-human primates as well. So that's not it. Gotta keep looking, but I think I need a nap. Without support for dismissing chicken studies, the reasoning seems to be: the chicken eyes are shaped like human eyes and respond like human eyes to some degree; so if the monkey eyes don't respond like the chicken eyes, the human eyes won't. But they did. And that's science. Thanks for the dialogue. It's actually been very helpful and informative. Cathy > Gotta keep looking, but I think I need a nap. > [quoted text clipped - 8 lines] > > Cathy Perhaps you were napping instead of reading the fine print, where Morgan/Megaw stated that primate eyes respond differently to myopic defocus than do chicken eyes. Proposing a hypothesis is one thing, but finding a clinically useful paradigm is another. Anyhow, what was the point of your pecking? DrG > Perhaps you were napping instead of reading the fine print, where > Morgan/Megaw stated that primate eyes respond differently to myopic defocus > than do chicken eyes. My reading of the fine print is that different animals responded differently in a quantitative sense to lenses of different powers. Accuracy and a wider range of lenses were the stated parameters of interest. For that we are to dismiss the parallels with human eyes found in Stone/Flitcroft? > Proposing a hypothesis is one thing, but finding a clinically useful > paradigm is another. Is this why the chicken studies are not useful? They're not in a clinical paradigm format? Ok. That makes some sense. > Anyhow, what was the point of your pecking? To sort out the kernels of corn in the "bifocals are plus lenses" position. The studies, and finding out how to look for them, were all a bonus. > DrG > Sorry, but I got lost in your translation about accommodation. > > > > If you know, what's the scientific support for poo-pooing chicken > > studies? Seems they're on the right track since they can induce, then > > uninduce, our different situations at will. Or is it just principle, > > that chickens aren't humans? Cathy> Monkey primate eyes do the same thing as the chickens -- the change their refractive status as the accommodation-signal is changed. Further -- to end the "heredity" debate, the left eye will respond to a contact lens (of say 1.0 diopter) by DIVERGING in refractive status from the right eye -- thus proving the concept that "refractive control" is in the accommodation signal. There are "primate-monkeys" so of course DrL will now argue that it can not -- must not -- be true for "primate-human" eyes. And of course he is right -- because no one can perform that experiment on humanes. DrL wins again. Best, Otis Engineer ******** > The scientific support for poo-pooing chicken studies is in the > Morgan/Megaw bibliography pertaining to primate studies(you should have [quoted text clipped - 6 lines] > > DrG > Cathy> Monkey primate eyes do the same thing as the > chickens -- the change their refractive status > as the accommodation-signal is changed. It is true that they respond to hyperopic defocus similarly. They do not, however, respond the same to myopic defocus. Please tell the truth for once in your life, man. Also, this has nothing to do with accommodation, so get that out of your mind as well. > Further -- to end the "heredity" debate, the left eye > will respond to a contact lens (of say 1.0 diopter) [quoted text clipped - 5 lines] > now argue that it can not -- must not -- be true > for "primate-human" eyes. I did not say it must not be true, I said that extrapolating from chicken eyes to humans is quite a flight. But this is the realm of science, either to prove or disprove experimentally. DrG Cathy, don't presume that the docs here cannot follow your reasoning because they disagree. Vision scientists do chick studies because they think they are on the right track. What is wrong with chick studies? Chicken eyes are not precisely analogous to human eyes. Chickens do not read. Chicken studies are done on very, very young animals, not mature animals, and not on human children. You don't know if the math applies to human children, or humans at age 40. The human visual system is a biophysical system, not a set of camera lenses. Flitcroft is suggesting that the other dimensions of the eye, besides the axial length, may have a bearing on myopia development. All of us, including you, need to keep an open mind about what come to light about the HUMAN visual system, at various ages. It is not in fact true that just removing minus lenses or putting on plus lenses removes myopia in humans, of all ages. "Neat" if that were the case, but it isn't. None of us can just make assumptions about any of this. I don't assume that human myopia is irreversible. There is much yet to learn about myopiagenesis, and the factors that affect it. You cannot think you're smarter than all the vision scientists,who are busy doing experiments and gathering data all the time, do you? Fran `````` > > Consistent with the work of Morgan/Megaw, and others, with chickens, who > > state the effect of a high plus lens which far exceeds the natural myopic [quoted text clipped - 29 lines] > > Cathy > > Consistent with the work of Morgan/Megaw, and others, with chickens, who > > state the effect of a high plus lens which far exceeds the natural myopic [quoted text clipped - 19 lines] > feet. Greater myopic defocus than the natural optics of the eye can be > achieved only with a plus lens. All myopes have myopic defocus at all distances beyond their far point and they progress despite this. The formula gives the accommodative demand, I don't know what you mean by "to neutralize". If you mean "reduce accommodative demand to zero", then a plus lens is required at all distances and the power of the plus lens is different for each distance. Assuming that the idea that reducing accommodative demand to zero for all distances will prevent myopia, how can you achieve this? > If you know, what's the scientific support for poo-pooing chicken studies? > Seems they're on the right track since they can induce, then uninduce, our > different situations at will. Or is it just principle, that chickens aren't > humans? The chicken studies were great studies of the process of emmetropization in congenital refractive error. They are poo-pooed as a tool to understand developmental refractive error (refractive error that develops after babyhood) because THEY WERE NOT STUDIES ABOUT IT. Dr Judy > Until now, I had no good reason to prefer to be a chick. Oops, I haven't > lost you because of the cheep joke, have I? > > Cathy > > The math won't change. Using the formula 1/distance in meters, all > > distances require a negative lens to neutralize, even if you can see 1000 [quoted text clipped - 10 lines] > accommodative demand to zero for all distances will prevent myopia, how can > you achieve this? Yes, I was unclear using the formula, but somehow you've picked up what I was trying to point out: a plus lens is required at all distances to reduce accommodative demand to 0. The ultimate point is that putting a net minus (bifocals) on a myope doesn't push him over to greater myopic defocus than when no glasses are used (natural optics of the eye). You can't substitute the use of a net minus lens for plus, then bemoan the failure of plus lens therapy for controlling myopia progression. There are more, but these three articles got me digging my heals in on this topic. They're not about congenital refraction errors. Investigation Ophthalmology & Visual Science 2003;44:2818-2827, titled "Potency of Myopic Defocus in Spectacle Lens Compensation", by Ziaoying Zhu, Jonathan A. Winawer, and Josh Wallman. Stone/Flitcroft's "Ocular Shape and Myopia" (Ann. Acad. Med. Singapore, vol. 33) and in the same publication, "Using Natural STOP Growth Signals to Prevent Excessive Axial Elongation and the Development of Myopia" by J. Morgan and P. Megaw. Cathy > The chicken studies were great studies of the process of emmetropization in > congenital refractive error. They are poo-pooed as a tool to understand > developmental refractive error (refractive error that develops after > babyhood) because THEY WERE NOT STUDIES ABOUT IT. > > Dr Judy > Yes, I was unclear using the formula, but somehow you've picked up > what I was trying to point out: a plus lens is required at all [quoted text clipped - 16 lines] > > Cathy Not to ruffle your feathers, but you seem to be reading more into these papers than is there. The key words are "myopic defocus," and not "accommodation." Even with a plus 10 diopter lens, accommodative demand is not zero at all distances. Otis would tell you that a child can/will read at 3 inches (go figure). Then, we also have to digest the information that suggests that myopes tend to progress in myopia at a faster rate than emmetropes, as well as the information that suggests children who do not wear their myopic correction progress faster than those who do. In comparing chicks to primates, we have to digest the fact that that the chicken choroid can increase in thickness to a far greater degree than primate choroids, and that this thickness increase responds to myopic defocus to change the eye shape. Apparently, researchers find chicken eyes entertaining because they can be manipulated so easily to change their direction. Also, they work for chicken feed. DrG > Not to ruffle your feathers, but you seem to be reading more into these > papers than is there. The key words are "myopic defocus," and not [quoted text clipped - 14 lines] > > DrG Oh, dear. We're not monkeying with the text now, are we? The key words are "greater than". You paraphrased it yourself a few posts back: "The key here is inducing a greater myopic defocus than the natural optics of the eye, and whether it works on humans." The accommodative demand formula gives the measurement of defocus so that a minimum minus lens can be prescribed for far point focusing. Pick any distance. With a plus 10 diopter lens, the scale is moved. The demand on accommodation is changed such that the minimum minus prescription needed for focusing at a desired distance is greater than without the +10 lens. The demand (and defocus, where applicable) at all distances is changed. As for the digestion issues, whether the rate of progression in myopia for all mentioned is faster or slower, it's only been shown to happen with defocus that is "less than or equal to" their vision without lenses, whether or not there is actual defocus at any specified distance. The comparison made above between choroids also is only one of degree. It doesn't dispute that thickness increase and eye shape change are happening for both. ... while the monkey researchers work for peanuts. Cathy >> Not to ruffle your feathers, but you seem to be reading more into >> these papers than is there. The key words are "myopic defocus," and [quoted text clipped - 40 lines] > > Cathy The fact is that the papers you are quoting also say that the reaction to myopic defocus as STOP signals in chickens has not been reproduced in mammals. Choroidal thickening cannot account for much more than a diopter of refractive change in primates. However, if such a paradigm were found to be successful in humans, it would be an interesting thing. But I dare say that the mechanism no longer seems to be directly related to accommodation, and on that all authors seem to be in agreement. The research speaks quite clearly, and there really is no need for reading more into it. DrG > The fact is that the papers you are quoting also say that the reaction to > myopic defocus as STOP signals in chickens has not been reproduced in [quoted text clipped - 10 lines] > > DrG Who are you talking to? Has your auto-reply message been sent by mistake? Where's the other DrG? I'll take it my argument was good except for the fact that the future isn't history. You again spin the reports, giving the less wary reader the impression the plus lens test was done on mammals and was not successful. The fact is, from the bibliography, what failed to produce a STOP signal was a lens removal test; myopic defocus was equal to, not greater than, the natural optics of the eye. The fact is that Flitcroft 2004 acknowledges "it still remains unclear whether near work comprises an independent risk factor", not that the mechanism is no longer thought to be related to accommodation. I have not read more into it. I have read what tools were used. I have read the results those tools produced. These papers, offered and defended by you to prove otherwise, show that plus added to a minus lens is not the same as plus only. That is what's clear. You offered a paradigm for consideration that you knew you did not deem credible yourself. That is what's clear. Allow me to try out your reasoning this way. The use of plus lenses has been shown to provide different results than bifocals where it has been tested. The plus lenses haven't been used everywhere, so until they have been found to be different than bifocals everywhere, all efforts where they have been found to be different should be considered to have failed. But they haven't failed. And that's science. In other news: - Previously known to be flat, the earth is now round. On the other hand, it's been shown to be quite jagged in places, so maybe it's not round. - The planets are now revolving around the sun. Due to shifting the reference point, it turns out. - After years of studying the relative effectiveness of toothpicks for smashing chicken, monkey, and human heads, hammers are discovered to be the tool we've been looking for. What? No controlled study, so not interested? Ok. We'll continue our quest for the differences and similarities in head structure for the explanation of why toothpicks don't work to smash heads. Oh, and we'll call the toothpick a hammer while we're at it. Anyway, I have other things to do, too. It was good talking with you. Dr Judy's and your contributions have been indispensable and appreciated. No joke. Thank you. Cathy > Who are you talking to? Has your auto-reply message been sent by > mistake? Where's the other DrG? I'll take it my argument was good [quoted text clipped - 20 lines] > considered to have failed. But they haven't failed. And that's > science. (gibberish deleted) > Cathy First of all, I am talking to you and the rest of the group, not to myself. Offering paradigms for consideration and discussion neither implies endorsement nor non-endorsement. I started this thread with a discussion of the Stone/Flitcroft review article as an example of evolutionary thinking about myopiagenesis, and the concept of blur rather than stimulus to accommodation. Eager to defend the "excessive accommodation theory" and use of plus lens prevention, you jumped on the Morgan/Megaw paper as proof, even in the face of contradictory evidence provided by the authors themselves in their own bibliography. In one of the abstracts cited, minus lens-induced axial myopic changes in infant monkeys were either halted or reversed with brief periods of wearing plano lenses each day. In contrast, those monkeys fitted with +4.5D lenses for the same number and length of intervals exhibited compensatory myopic growth. Plus lenses have not been found to produce the same results across species. DrG Excellent! I had other articles by the same authors in the same years on the same subjects. Certainly something deserving followup. In the case of the tree shrews, -3D results = +3D results. (There's something fishy here.) Thank you. (No need to delete as gibberish.) Cathy > > Who are you talking to? Has your auto-reply message been sent by > > mistake? Where's the other DrG? I'll take it my argument was good [quoted text clipped - 45 lines] > > DrG > Offering paradigms for consideration and discussion neither implies > endorsement nor non-endorsement. I started this thread with a discussion [quoted text clipped - 14 lines] > > DrG Thanks to your clue naming the +4.5D lenses on monkeys, I have discovered my error as to the references I was using to say that no plus lens test has been done; that is, a plus lens greater than natural optics. After reviewing the correct abstracts, I see that the results in the plus lens test done on tree shrews support the notion that a short period of plus counters a full day of minus, but doesn't stop an emmetrope from migrating into myopia, even using lenses greater than the natural optics of the emmetropic eye. However, I challenge that it is a plus lens test in the sense we're talking about: bifocals on a myope vs. plus greater than the natural optics of the myope. You'll see the problem in a minute. Siegwart/Norton's purpose was to see if a plus lens would do any better than plano to stall an emmetrope's expected journey down myopia progression. Better than expected, plano prevented the start. (A STOP signal?) According to the previously known parameters, (1) compensation for -5D will be accomplished in 11 days and (2) removal of the lens for 45 min/day will reduce compensation by about half, the results with a plano lens should have been about -2.5 rather than -0.2. What's up with that? Plano on a tree shrew is better than lens removal? I was under the impression everyone considered plano an equal to unaided vision. There has to be an error in the study or tree shrews don't even have a common starting point with humans. The conclusion then states the plano lens is the success of the study, all other results showing myopic progression, and its success is because of the mostly focused images in that 45 minutes every day when plano was worn. Based on the results for -3D and +3D, they might have even supported Mike Tyner's insistence that the eye doesn't know whether the lens in front of it is minus or plus, except for the following: The oddity of the +5D results being better than the +3D results and the unexpected plano results are not accounted for, so let me try. Playing with the margins of error, the results for the +5D lenses in some cases are pretty close to the plano lenses, maybe sometimes better. I question how one can conclude, in light of the plano lens results not conforming to expected results, it was the plano lens that was the source which accomplished the purpose of maintaining emmetropia. The myopically defocusing +5D lenses accomplished the purpose, too, in some cases, supposedly. The entire group of +5D lenses outperformed the entire group of +3D lenses and even some of the +10D lenses outperformed some of the +3D lenses. Even if I'm off-base as to interpreting margins of error, the point remains that the +5D lens somehow outperformed the +3D lens as well as what the plano should have been expected to show at -2.5. What next is noticed is that the nearest visual stimuli is at one meter. Might not the refraction measurement be predicted to be -1D for the lens that ended the study mostly focused on the nearest stimuli? Nearest stimuli was made a point of interest by the authors, not by me. When working with diopters, it seems a useful bit of information for interpreting results. From the data presented and without reading anything into it, I note: The myopically defocusing +5D lens (equivalent to a -5D myope's defocus without lenses) resulted in -1.1D refraction, within tolerance for focusing on stimuli at one meter. Is this a STOP signal? Axial elongation hasn't exceeded its requirement for focusing on the stimuli provided. One can't avoid accommodation when that's what's put in front of your face. The +3D (equivalent to a +2D bifocal for the -5D myope) resulted in -3.1, a progression of myopia from both the plano's result of -0.2 and the previously known removed lens result of -2.5 in premise (2). Ironically, this net -3D myopic defocus from the point of view of the -5 myope shows a refraction difference of -3.1. A STOP signal based on which lens is used? This lens goes beyond the accommodation influence. There was no opportunity to progress more due to accommodation since nothing was within the 13" range for focusing. The myopic progression between -1.1D and -3.1D was due to axial elongation, while the progression from 0 to -1.1D was due to accommodation. The -3D more than prescribed and -5D more than prescribed groups should both be expected to increase their myopia, and they did, within tolerance of the refraction difference they were asked to produce. STOP signals? I think we've found them. We don't know what to do with them. As for the +10 lens? I don't know except to note that in trying to pull the emmetrope down to -5D, the +10 lens allowed only to -4D even while the vitreous difference increased more than the No Sub group. All other vitreous measurements follow the refraction measurement patterns. This same -5/+10 combination is what produced a STOP signal in chick for Morgan/Megaw, so I cede your point of not getting the same results across species. We may simply be looking for a bigger - to + ratio for mammals than for chicks, but that remains to be researched (my point). More on that in the monkey paragraph below. Also, the time required to fully compensate for the imposed hyperopic defocus does not match across species. Rhetorically, so what? That non-same result may, in fact, be a clue for predicting each animal's STOP signals. Essentially, though, this study looks like the same old thing. Only one plus lens had greater myopic defocus than what was strong enough to resolve itself to the visual stimuli. Is there really enough plus data here to consider it a plus lens test? It at least reiterates across species that no positive thing comes from minus (including less minus) lenses for myopes. The tree shrew abstract wasn't mentioned in your post, so maybe you've already dismissed this reference as support for Morgan/Megaw's implication of a plus lens test failure. The +4.5D monkey abstract evoked these observations. If "compensatory" myopic growth means -4.5D, the monkeys at +4.5 after -3 did worse than the tree shrews at +10 after -5. Ignoring that time patterns didn't match and distances are unknown for the monkey study, a +1.5D greater than expected resultant myopic defocus got you -4.5D myopia while a +5D greater than expected resultant myopic defocus got you -4.0D myopia. I'm not reading anything into it, just reading it, accepting it, and recognizing the only two plus lens data supplied from the point of view of myopic mammals actually show the greater the plus over expected resultant myopic defocus, the less absolute myopia resulted. Alas, two points on the graph only get you two points on the graph. At least a few more are needed to see a trend, even to say we looked but can't find the trend. I'm curious whether a dip occurred between +1.5 over and +5D over in chick studies, but not enough to look into it. For the meantime, I concur with your statement, fashioned to elicit feigned agreement, that plus lenses have not been found to produce the same results across species, but, if these two studies represent the best of the failures, you must concur that no effort has been made to see how plus lenses work for myopic mammals, i.e., how plus lenses work. And, of course, that bifocals, an across-the-board predictable myopia progression tool, are not the same as plus lenses, unpredictable as heretofore casually tested from an emmetropic point of view. I think the less cagey answer to give is that plus lenses haven't been researched as a myopia management tool so we can't reasonably predict the outcome if used for that purpose. We do know they work, though. As for the description of who's on which side, I'm not defending a theory; I hardly know any. I don't care how myopia starts; its progression just has to stop. I don't care about prevention; it's too late for those who've succumbed and not necessary for those who never will. I don't know proof, only evidence, and the math has to work. As always, what have I missed? (There's the proof I don't know proof.) Cathy > The +3D (equivalent to a +2D bifocal for the -5D myope) resulted > in -3.1, a progression of myopia from both the plano's result of -0.2 and [quoted text clipped - 6 lines] > and -3.1D was due to axial elongation, while the progression from 0 to -1.1D > was due to accommodation. Let me correct the last two sentences. All the axial elongation between 0 and -3.1D was caused by the all day wearing of the -5D lens. Elongation was stopped at -3.1 by 45 min/day of -3D lens. One meter of accommodation only influenced the +5D relief lens group as a STOP signal. Cathy > > > The math won't change. Using the formula 1/distance in meters, all > > > distances require a negative lens to neutralize, even if you can see [quoted text clipped - 21 lines] > the use of a net minus lens for plus, then bemoan the failure of plus lens > therapy for controlling myopia progression. Oh, you meant for myopes, my statements were in regard to emmetropes. You are incorrect, it is not necessary to use a plus at all distances to reduce net accommodative demand to zero for myopes. For example, a -1.00 myope looking at something 2 metres away will have a net accommodative demand of zero with a -0.5D lens. As far as the eye and light rays reaching the eye are concerned, this is exactly the same as a -0.50 myope with no glasses or an emmetrope wearing +0.50 or a +1.00 hyperope wearing +1.50. The emmetropes and hyperopes by and large do not become myopic, the myopes do. A -2.00D myope has a greater myopic defocus with his glasses off than a +2.00 hyperope does with his glasses off; yet the myope is quite likely to progress and the hyperope is quite unlikely to lose the hyperopia. The theory behind plus therapy advocates is unable to explain those two observations or why myopes develop in the first place, every myope walks around uncorrected with myopic defocus before getting glasses, if myopic defocus and plus lenses prevents/reverses myopia then no myopia should ever develop. Most hyperopes walk around with hyperopic defocus and do not become emmetropes. I'm waiting for the chicken researchers to breed a chicken that is hatched emmetropic then naturally becomes myopic at 10 days old without any manipulation, progresses in myopia for another 10 days, then stops progressing. That chicken will provide a model for human myopia and if any proposed prevention/reversal therapy works for that kind of chicken, I would consider it worth trying as a human clinical trial. Dr Judy > There are more, but these three articles got me digging my heals in on this > topic. They're not about congenital refraction errors. Investigation [quoted text clipped - 14 lines] > > > > Dr Judy I've just come back from my chicken coop (yes, I actually have chickens. The Mottled Java, "peckie" and the Exchequer Leghorn ("spotty") are my favorites) and I have completed my study. The two year olds are emmetropic 20/20 and the two month olds are 2D hyeropic and see 20/20. Retinoscope finding for the optics. How do I know they see 20/20? I use a modified Snellen chart, called "the Smellen chart". It contains various size drops of poop and feed pellets of three sizes. If they can peck out the feed from the poop, then I know they can see. --Larry > There are more, but these three articles got me digging my heals in on this > topic. They're not about congenital refraction errors. Investigation [quoted text clipped - 4 lines] > Natural STOP Growth Signals to Prevent Excessive Axial Elongation and the > Development of Myopia" by J. Morgan and P. Megaw. Cathy This is what happens for me. I have a selection of lenses that I can use to correct my vision to best corrected or slightly under minus. If i under correct my eyes by less than about 20/30 to 20/40 in daylight conditions then my eyesight very quickly becomes worse. If i then use a stronger prescription I find after a few days i can then reduce to some mid point. There are studies that support what I observe. http://www.newscientist.com/news/news.jsp?id=ns99993082 However if i use a full strength prescription i quite quickly find it is too weak. Which suggests there is more to it than what was found in the above study. No prizes there i guess. I also find that the best seeing eye tends to get better while the worse seeing eye gets worse. Therefore it is necessary to ensure my eyes are balanced. This can be time consuming. I think studies like the one above might be flawed because the amount of reduction is too high at - .75D. For some children this would have created an almost intolerable amount of discomfort. It would make more sense to correct to a specific understrength acuity and then ensure that this acuity does not worsen and maintain that acuity over the study. Whatever is going on it seems clear that human vision is not really comparable to chicken or monkey vision. Andrew > Whatever is going on it seems clear that human vision is not really > comparable to chicken or monkey vision. What's clear that your "refractive state" is a result of two components, if you're young and myopic. The "accommodative" component is muscle posture, and it changes day-to-day, and disappears around age 45-50. The "axial" component shows measurable changes in axial length, gradually growing longer but rarely or never growing shorter. If it changes back and forth day-to-day, it's accommodative. -MT > > Whatever is going on it seems clear that human vision is not really > > comparable to chicken or monkey vision. [quoted text clipped - 9 lines] > > If it changes back and forth day-to-day, it's accommodative. Its possible you are completely correct. I can let you know in 15 months. However since many people can still accommodate into their late 50's we might have to wait a bit longer. > Its possible you are completely correct. I can let you know in 15 > months. > > However since many people can still accommodate into their late 50's > we might have to wait a bit longer. Although the figures are usually true there certainly are people who can still accommodate in their fifties. I am 51, and have a near point of 8 inches. No problems, really, at any distance right now. Who knows what the future will bring, but I just wanted to set the record straight. Cheers, Francine Hi Andrew, I think there is a critique of the Oleary study, and lots of other interesting stuff about myopia, here: http://vision.berkeley.edu/wildsoet/myopiaNews/controllingMyopia.html Cheers, Francine > Whether or not this idea of plus lens therapy will eventually be found to > work in humans, my only point throughout has been that less minus is not > plus, so the outcomes of each (less minus vs. plus) can't be expected to be > equivalent. Less minus on a myope certainly _is_ equivalent to plus on an emmetrope. The eyeballs don't care whether the lens is convex or concave, but only how much blur it produces. -MT Cathy, I'm sure you haven't come up with articles that the rest of us haven't seen. We are all reading the same articles but apparently coming up with different conclusions. > What I have read in the abstracts and articles is that minus lenses (not the > +3.00 prescription you refer to in your emmetrope example) were placed on > non-myopes who quickly became myopes. One can't make a blanket statement like this; it doesn't fit the facts. You are generalizing from a series of articles and experiments, the conclusions of which even the researchers are not in agreement about. What does this call for? Further experiments, not premature unequivocal conclusions. Please note these facts: (1)The non-myopes who became myopes were not humans, but ANIMALS. Animal studies are commonly done, but cannot decisively substitute for human trials. (2) Also - the animals' eyes were forced into a situation where they wore hoods with minus lenses, full-time. (3) The experiments were done on animals during a crucial formative period, that would correspond to human INFANCY. (4) Human infants are never forced into a situation like (3). (5) Using the strong plus lenses worked on animals during their formative period, AFTER they had induced myopia. (6) As Dr G and others have said, human myopia progresses without the application of lenses. (7) Not all individuals become myopic, even given an environment of intensive near work. One cannot conclude that all animals or all humans will develop myopia, because in the real world things this does not occur. It may be that during the formative period all human infants would develop myopia if restrained and fitted with minus-lens hoods. This is never going to happen, so we will have to find the truth by other means. What (5) suggests to me is that in myopia-prone individuals the use of the plus lens for prevention may have merit. I have said this more than once. Still, it is not a conclusion that can easily be reached. We don't know WHICH people are prone to myopia without finding a HUMAN gene for myopia, like the myopia gene called ZENK that has been found in birds. (6) and (7), the variable tendency in human individuals to develop myopia, suggest that this gene may well exist. If and when it is found, I would say that an experiment might be done using individuals possessing this gene. It would be difficult to employ the placebo effect in such a case, because the use of a plano lens would be too easily detectable. And any other lens that created a blur might cause myopia, too. Still, once the myopia gene(s) is isolated, it will be easier to develop a strategy for prevention and reversal of myopia. To tell you the truth, I'm not all that keen on the way the placebo effect is used in clinical studies. But that's another story, entirely. Fran ------------ >>> And yet, myopia progression is not significantly slowed when the 6D >>> myope uses -3.00 at near. At the same time the non myope's +3.00 [quoted text clipped - 51 lines] > > Cathy Hello Francine, Pleased to see you continue your interest in an anlysis of the behavior of the natural eye. With your permission -- some commentary: > Cathy, I'm sure you haven't come up with articles that the rest of us > haven't seen. We are all reading the same articles but apparently coming up > with different conclusions. Right-on, Fran. People with exactly the SAME TRAINING will reach exactly opposit concludions whe looking AT THE SAME EXPERIMENTAL DATA. This was the problem Dr. W. H. Bates had. He saw things "differenetly" -- and the dust still has not settled!!! > > What I have read in the abstracts and articles is that minus lenses (not the > > +3.00 prescription you refer to in your emmetrope example) were placed on > > non-myopes who quickly became myopes. Actually, what happend to these natural eyes with mostly positive refractive states is that the refractive status OF THE ENTIRE POPULATION MOVED NEGATIVE, RELATIVE TO THE POPULATION THAT WAS NOT WEARING THE IMPOSED MINUS LENS. There are two possible conclusion you can draw from this: 1. The minus lens CAUSES THE EYE TO BECOME DEFECTIVE. 2. The natural eye sets, or controls its refractive status to the average value of accommodation -- and a natural scientific process. > One can't make a blanket statement like this; it doesn't fit the facts. This depends on WHAT you are looking for. 1. The cause of "DEFECTS". 2. Or wish to establish if the natural eye is "dynamic". Depends on your backgound and what you are looking for. > You are generalizing from a series of articles and experiments, the conclusions > of which even the researchers are not in agreement about. People in medicine very seldom agree on very much. But they can and do have STRONG OPINIONS -- which explains the necessity of the "second opinion", in various situations. What does this > call for? Further experiments, not premature unequivocal conclusions. "Perfect" conclusions exist in mathematics. > Please note these facts: > > (1)The non-myopes who became myopes were not humans, but ANIMALS. Animal > studies are commonly done, but ca |
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