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Medical Forum / General / Vision / July 2007Why incompetent bifocal studies fail.
Subject: Why the bi-focal (plus) studies PRESUMABLY fail. The bifocal (strong-minus on top -- VERY weak plus on bottom) has been used for the last 50 years. When the study is done CORRECTLY (i.e., the Oakley-Young) study, the minus group goes DOWN at a rate of -1/2 diopter per year. The plus group does not go down. The data was collected over four years. Further over 200 children were used in the study, which is necessary for statistical accuracy. When a group of majority-opinion ODs run the study, they automatically over-prescribe the minus (as described by Judy for "Best Visual Acuity") by up from -1 to -2 diopters, and the plus is used WITH NO INSTRUCTIONS ON HOW TO USE IT!!! The result of this over-prescribed minus is that the eye goes down because of that minus. The better idea would be to avoid the minus an INSTRUCT the person in the correct use of the plus. Thus the person's insight an motivation would HAVE TO BE PART OF THE STUDY. Here is some commentary about this issue for your interest. ========== Dear Mike, Here Judy describes how she prescribes, not for 20/40 or 20/20, but for "Best Visual Acuity". We know the risks of an over-prescribed minus. (Massive body of scientific facts and data.) Judy turns a deaf ear, and a blind eye to this data -- claims it "does not exist". The second-opinion ODs acknowledge it -- and attempt to "restrict" the use of the minus as much as possible -- and use the plus where the person will ACTUALLY USE IT SYSTEMATICALLY. You will find statements by "majority-opinion" ODs that the "plus" does not "work" for prevention. These are the so-called bi-focal "studies". Why do they fail??? Because of this over-prescription policy -- which these majority opinion ODs will never acknowledge to the person himself. The over-prescribed minus just defeats the entire purpose and effect of a proper-strength plus -- when it is correctly understood AND USED by the person himself. Why do they get away with it??? Because they run BLIND studies, which means the person is NEVER informed about plus-prevention. It also suggests that... 1. ...you were wise to quit cold-turkey at -2.75 diopters and 20/200 (yeah, I know it was a struggle), and 2. Why your VA slowly cleared to the present 20/40 (which is good, considering that you pulled your vision back before it was too late. 3. Why it is good to put together your own trial-lens kit to get an ACCURATE refractive STATE by your OWN measurement. This explains ... 4. Why you measure -1 diopter, when your OD measured -2 diopters. Keep building your knowledge of these issues -- and protect your distant vision -- for life. This discussion is between Judy and Andrew from i-see. ================ Re: Fine tuning your vision exercise routine drjudywrote: Judy>>The determination of refractive error is not based on which lines are read. Judy> Some of the lights and instruments are used to objectively measure refraction (objective meaning the patient isn't actively involved) by watching reflections from the retina. The "which is better one or two" business is used to refine the refractive with the subjective opinion of the patient. Endpoint is when adding more minus does not improve and adding more plus does blur the chart. The final best corrected acuity is then measured. [Thus if the child's retina is capable of 20/10 vision, then, even if the child read 20/40 with NO LENS, this child will receive a lens of from -1 to -2 diopters. Judy should always explain this "policy" of hers -- but she never does. The child and parents are oblivious to the consequences of this majority-opinion policy. OSB] Judy> Doctors do not refract to achieve a particular acuity, the aim is to provide the clearest vision with the least minus or most plus. [A very accurate description of this over-prescription policy. OSB] Judy> Otis may suggest using under-powered glasses that make a particular line "just readable" but that is not a technique used by eye doctors. [This is NOT my suggestion. I suggest what Mike did -- check your visual acuity using your own Snellen. If you are passing the LEGAL 20/40 line (3/4 inch letters at 20 feet), the you must ask yourself -- why was I prescribed a -2 diopter lens -- when I do not need it. This is exactly what I mean. No lens at all, not a "weaker" lens -- PROVIDED you pass the legal standard. If you do not, then you must get a minus for driving. OSB] Just one man's opinion. Otis On Jul 27, 11:21 pm, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > When the study is done CORRECTLY (i.e., the Oakley-Young) > study, the minus group goes DOWN at a rate of -1/2 diopter per > year. The plus group does not go down. The data was > collected over four years. really? so if the results don't come out the way you believe they should then the study is done incorrectly? well I bet there has been a half-dozen bifocal studies and ALL of them except for the one you believe show that bifocal use has no or negligible effects on myopia progression. but I guess they ALL are wrong huh? what about Chung's study on myopia undercorrection-- that's wrong too? and what about Goss et al.'s study on overminusing children -- that's wrong too? and what about the studies where myopes take off their glasses to read, and where plus readers are used, etc. etc. I suppose according to you they are ALL done wrong. I guess when a study is performed that reaches a different conclusion than you believe it should, then the study is wrong-- right? You sure are a critical thinker aren't you Otis. Your objectivity is overwhelming. What a scientific mind you have! >Subject: Why the bi-focal (plus) studies PRESUMABLY fail. > >The bifocal (strong-minus on top -- VERY weak plus on bottom) has been >used for the last 50 years. My guess would be at least 53 years. I must have been one of the first victims, though I was not in a study. The OD said the idea was brand new... ... >When a group of majority-opinion ODs run the study, they >automatically over-prescribe the minus (as described by Judy for >"Best Visual Acuity") by up from -1 to -2 diopters, My first bifocals were plano over +0.75. >and the plus is used WITH NO INSTRUCTIONS ON >HOW TO USE IT!!! The doctor told my parents to make sure I always read through the bottoms of the lenses, and that I kept the book a minimum distance away from my eyes. What he didn't do was determine whether I _could_ read through the plus part at that distance. When I discovered I couldn't, the distance was hard to fake, but it was comparatively easy to fudge the angle and read through the very bottom of the clear part of the lenses. Obviously that didn't help my myopia. When I couldn't pass the school vision screening after a year of this "therapy", they started adding minus above the same +0.75 bifocal area. If I couldn't read through it before, no way could I read through it now. So my only choice was to read through the stronger and stronger minus, with predictable results. >The result of this over-prescribed minus is that the eye goes >down because of that minus. The better idea would be to avoid the >minus an INSTRUCT the person in the correct use of the plus. > >Thus the person's insight an motivation would HAVE >TO BE PART OF THE STUDY. I have no idea what might have happened had my "therapy" been done differently. Had I been an ordinary kid who read a few minutes a day, maybe I could have been enlisted to make a therapeutic exercise out of it. But reading and other close activities were my life, and there were only a few minutes a day when I ever looked beyond arm's reach. Maybe for the kid who read for fifteen minutes a day, +0.75 was appropriate, like lifting a 75 pound free weight for fifteen minutes and then moving on to other activities. I needed something more like those two pound wrist weights that you can wear all day... I've never met anyone who experienced "plus therapy" as a child and benefited from it. Has anyone? >The "which is better one or two" business is used to refine >the refractive with the subjective opinion of the patient. >Endpoint is when adding more minus does not improve and >adding more plus does blur the chart. This was my other complaint about all of my OD experience. Nobody would ever define "better" for me, and the stimulus was always restricted to fuzzy gray letters projected on the opposite wall of a dark room. More minus put more "edges" on the letters, like adding extra sharpening in Photoshop, so it must be "better", right? >Judy> Doctors do not refract to achieve a particular acuity, the >aim is to provide the clearest vision with the least minus [quoted text clipped - 6 lines] >particular line "just readable" but that is not a technique >used by eye doctors. The lenses I ended up with were very good for reading the union label on the bumper sticker of the car ahead of me, but not so useful for quickly knowing how far away that car was, or determining its relative speed... "Clearest" vision depends on many factors in addition to spatial resolution, and the appropriate balance may be different for different people. Loren > On Fri, 27 Jul 2007 20:21:28 -0700, "otisbr...@pa.net" > [quoted text clipped - 86 lines] > > Loren Very interesting! > On Fri, 27 Jul 2007 20:21:28 -0700, "otisbr...@pa.net" > [quoted text clipped - 86 lines] > > Loren Thanks for contributing. I think you'd hear bunches of different outcomes if all the people who were given bifocals to stave-off myopia were to post. It simply represents the wide variability within the population, and the fact that using a bifocal add (or separate plus readers) DOES NOT have any effect on reducing myopia. However, if even one person were to claim it worked, Otis would come forth and claim that person as proof positive that "the plus" is effective. On Jul 27, 11:21 pm, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > Subject: Why the bi-focal (plus) studies PRESUMABLY fail. > [quoted text clipped - 8 lines] > Further over 200 children were used in the study, which > is necessary for statistical accuracy. Not so accurate. If you read the actual study, you find that Oakley- Young decided to omit the results from some control group subjects and then used other control subjects' results several times. Control group and treatment group were not matched for age of first myopia or for age/sex distribution. Dr Judy On Jul 27, 11:21 pm, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > We know the risks of an over-prescribed minus. (Massive body > of scientific facts and data.) Please provide human clinical trial that supports your statement of the risks of minus lenses. Dr Judy > On Jul 27, 11:21 pm, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > [quoted text clipped - 5 lines] > > Dr Judy No reply. No surprise. Here are two human studies wherein non myopic subjects wore truly overprescribed minus (up to -4 too much minus) for up to 7 years and "gasp" DID NOT BECOME MORE MYOPIC OR PROGRESS MORE THAN NON WEARERS!!!!! PubMed citation number: 10326961 "Does overcorrecting minus lens therapy for intermittent exotropia cause myopia?Kushner BJ. Pediatric Eye and Adult Strabismus Clinic, Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, USA. bkushner@facstaff.wisc.edu Overcorrecting minus lens therapy has been used as a treatment for intermittent exotropia. It is based on the principle that an exotropic deviation will be decreased by stimulating accommodative convergence with additional minus power in spectacles.... Seventy-four patients with intermittent exotropia were treated with overcorrecting minus lens therapy for at least 6 months (6-month treatment group), and a 34- patient subset of them received overcorrecting minus lens therapy for 5 years (5-year treatment group). ..... Differences in the change in refractive error (myopic shift) were not statistically significant (t test), and the differences are clinically unimportant. CONCLUSION: Overcorrecting minus lens therapy for intermittent exotropia does not appear to cause myopia." and "Pub Med # 2771338 Changes in refractive error for exotropes treated with overminus lenses.Rutstein RP, Marsh-Tootle W, London R. School of Optometry Medical Center, University of Alabama, Birmingham. ... Overminus lenses means additional minus power over the lenses required to correct the refractive error at distance. Forty exotropic patients, ages 1 to 15 years, were prescribed overminus lenses (-0.50 D to -3.75 D) for a period of 9 to 86 months. The mean annual changes in refractive error for hyperopes (-0.13 +/- 0.44 D, N = 15), emmetropes (-0.26 +/- 0.37 D, N = 17), and myopes (-0.75 +/- 0.77 D, N = 18) were similar to values reported in the literature for nonexotropic children." So I have provided two long term, human studies (one controlled, one retrospective) as evidence that overprescribed minus lenses do not cause or increase myopia. Still waiting for your reply with contrary evidence. Dr Judy > No reply. No surprise. Here are two human studies wherein non myopic > subjects wore truly overprescribed minus (up to -4 too much minus) for I had not seen the second one you listed. Thanks. There is another one you didn't list. Here it is. It was initially performed to investigate the possibility that overminusing might PREVENT myopia progression. It didn't pan out but the data also shows it didn't cause accelerated "stairstep myopia" either. Sorry Otis! ============== Goss, D. (1984) Overcorrection as a means of slowing myopic progression. Am J Optom Physiol Opt., Feb;61(2):85-93. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstra ct&list_uids=6703013&query_hl=3 Thirty-six subjects (18 males and 18 females) ranging in ages from 7.38 to 15.82 years received an overcorrection of 0.75 D over the power required to correct their myopia exactly. These 36 experimental subjects were matched by control subjects selected at random from the files of the Indiana University Optometry Clinics. The criteria used in matching were sex, beginning age, beginning refractive error, and duration of time covered by the record. The mean rate of change of refractive error for the experimental group was (minus indicating increase of myopia) -0.49 D/year (range, +0.37 to -1.95 D/year) on retinoscopy and -0.52 D/year (range, +0.21 to -1.32 D/year) on subjective refraction. The mean rate of change for the control group was -0.47 D/year (range, +0.06 to -2.03 D/year) on retinoscopy and -0.47 D/year (range, +0.28 to -1.72 D/year) on subjective refraction. Rates for the experimental and control groups were not significantly different. The results of this study do not support the hypothesis that an overcorrected myope has a lower rate of increase of myopia than a myope wearing a conventional spectacle correction. |
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