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Medical Forum / General / Vision / March 2007Defocus
Consider the following abstract: -------------------------------------------------- Curr Biol. 2006 Apr 4;16(7):687-91. Myopia: the importance of seeing fine detail.Schaeffel F. Section of Neurobiology of the Eye, University Eye Hospital, Tuebingen, Germany. frank.schaeffel@uni-tuebingen.de Eye growth and myopia development are controlled by the retina. What properties of the image tell the retina how the eye should grow? A recent study has shown that, in chickens, fine details are necessary to prevent the development of myopia. Should we carefully avoid any defocus to avoid becoming myopic? -------------------------------------------------- Comments? Dear "L", Subject: Please define "De-Focus" -- EXACTLY Hunting Eskimos have normal refractive STATES from zero to +3 diopters. http://www.geocities.com/otisbrown17268/AccoGraph.html Using this model of accommodation, (input environment, versus output lens power), with a typical refractive STATE of +1 diopter, please tell me at what point "de-focus" will exist for this Eskimo's retina. Remember this Eskimo will have 20/20 vision. The age will be less than 30 years. The range of accommodation (free movement) will be seven diopters, from +1 diopter to -6 diopters. There will be "blur" is the Eskimo is asked to read the Snellen THROUGH a +2 diopter lens. The Eskimo will read 20/20 through a +1 diopter lens. There will be "blur" if the object is closer than 6 inches (-6 diopters). Are you saying that blur exists for the normal eye between 6 inches to infinity. Please explain your theory of defocus more accurately. Best, Otis > Consider the following abstract: > [quoted text clipped - 12 lines] > > Comments? On Mar 3, 9:05 am, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > Dear "L", > [quoted text clipped - 49 lines] > > - Show quoted text - You are talking about refraction. You need to tell me more, such as how this Eskimo accommodates. I would also like to know if the Eskimo's eye is prolate or oblate. DrG Dear "L", I see you are going to avoid ansering the question by: 1. Asking irreverant question and by 2. Changing the subject. You truly have no definition of "defocus" at all. "...but, the boy said, "the Emperor has no clothes on..." Best, Otis > On Mar 3, 9:05 am, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > [quoted text clipped - 59 lines] > > - Show quoted text - On Mar 3, 9:30 am, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > Dear "L", > [quoted text clipped - 77 lines] > > - Show quoted text - Then, you really have no business posting in this thread if you have no understanding of these concepts. Goodbye. DrG Dear "L", You have no business using the word, "Defocus" when you can not even define it. This is just a bull sh.t word you use to bambozle the public. So again, please answer the question, as per the accommodation diagram. By "defocus" do you mean that when you ask the Eskimo to read the Snellen through a +3 diopter lens he will see blur (defocus). If that is what you mean -- then I will AGREE with you. Also, if you mean that if you ask the Eskimo to read at 4 inches (-10 diotpers) he will see blur (defocus) then again I will agree with you. The issue is the range between the two "stop" points. And the question I ask is this, "does the Eskimo have de-focus between those two stop points -- or not. This is a easy question to answer. If you had any techinical or engineering sense -- you could and would answer the question. Otherwise, I would agree that optometrists do not understand the behavior of the NORMAL accommodation system. And that it is more an engineering-scientific issue, rather than an optometry issue. Best, Otis > On Mar 3, 9:30 am, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > [quoted text clipped - 88 lines] > > - Show quoted text - On Mar 3, 12:10 pm, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > You have no business using the word, "Defocus" when > you can not even define it. You clearly are not interested in a dialogue. > This is just a bull sh.t word you use to bambozle the public. Only 605 citations came up when I used "defocus" as the search term. > By "defocus" do you mean that when you ask the Eskimo > to read the Snellen through a +3 diopter lens he will see > blur (defocus). If that is what you mean -- then I will AGREE with > you. Good. > Also, if you mean that if you ask the Eskimo to read at > 4 inches (-10 diotpers) he will see blur (defocus) then > again I will agree with you. Good. > The issue is the range between the two "stop" points. > > And the question I ask is this, "does the Eskimo > have de-focus between those two stop points -- or not. Then, tell me about that Eskimo's accommodation. > Otherwise, I would agree that optometrists do not > understand the behavior of the NORMAL accommodation > system. And that it is more an engineering-scientific > issue, rather than an optometry issue. I think even an engineer would understand what I am talking about. Would you agree that the Eskimo would experience defocus at 1 meter? DrG On Mar 3, 7:30 am, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > Dear "L", > [quoted text clipped - 7 lines] > > "...but, the boy said, "the Emperor has no clothes on..." === Is anybody else here as struck by the astounding irony of this post as I am?? Can we just linger on it for a moment..... Hey, Otis: care to answer a few direct, valid questions?? see: http://nbeener.com/NDB_OSB_Qs.txt > Consider the following abstract: > [quoted text clipped - 12 lines] > > Comments? Only that the vast majority of myopic humans start out with fine details, as a rule... "Dr. Leukoma" <drg@leukoma.com> wrote in news:1172930214.859581.263620@ 64g2000cwx.googlegroups.com: > Consider the following abstract: > [quoted text clipped - 12 lines] > > Comments? Are chicks foveate?? I think some birds, parrots for example, have two regions of high acuity vision, and change fixation when appropriate. Also, what is the chicks accomodative range?  SignatureScott Reverse name to reply > "Dr. Leukoma" <d...@leukoma.com> wrote in news:1172930214.859581.263620@ > 64g2000cwx.googlegroups.com: [quoted text clipped - 18 lines] > Are chicks foveate?? I think some birds, parrots for example, have two > regions of high acuity vision, and change fixation when appropriate. I think they are non-foveate. > Also, what is the chicks accomodative range? Schaeffel claims 15-17 diopters, of which 8 is corneal. I googled chicken and accommodation and got a wide range of responses, mostly having to do with ways of preparing and serving chicken. Accommodation has a number of meanings. > -- > Scott > Reverse name to reply- Hide quoted text - > > - Show quoted text - "Dr. Leukoma" <drg@leukoma.com> wrote in news:1173107944.976310.247130@ 30g2000cwc.googlegroups.com: >> "Dr. Leukoma" <d...@leukoma.com> wrote in news:1172930214.859581.263620@ >> 64g2000cwx.googlegroups.com: [quoted text clipped - 34 lines] >> >> - Show quoted text - My gut tells me that the chick literature involves a developmental process, and that human myopiagenesis involves a mature adaptive process. I don't think that in the long run anything from the chick literature will point us to anything applicable beyond infancy. SignatureScott Reverse name to reply > "Dr. Leukoma" <d...@leukoma.com> wrote in news:1173107944.976310.247130@ > 30g2000cwc.googlegroups.com: [quoted text clipped - 52 lines] > > - Show quoted text - Maybe, unless one regards humans as having a prolonged developmental period. DrG "Dr. Leukoma" <drg@leukoma.com> wrote in news:1173134016.551813.100400 @h3g2000cwc.googlegroups.com: > Maybe, unless one regards humans as having a prolonged developmental > period. > > DrG I don't know about retina, or eye shape, but there are pretty well defined neurogenic periods of brain development. The developmental neuroscientists down the hall from me can provide more specific information, but I've yawned through enough of their talks to know that these developmental periods have fairly clear endpoints. If we insist on thinking the brain is involved, there really seems to be something quite different about developmental periods. Stuff like bone growth, obviously, is different. Maybe eye growth is as well, but any defocus information is going to be neural, so I'll lean toward some development process. In any case, if I were refereeing a paper or scoring a grant in the area, I'd certainly expect a paragraph or two acknowledging that these might be two separate processes. Another direct question would be are the processes that go on in the chick adaptive, or developmental? SignatureScott Reverse name to reply > "Dr. Leukoma" <d...@leukoma.com> wrote in news:1173134016.551813.100400 > @h3g2000cwc.googlegroups.com: [quoted text clipped - 23 lines] > Scott > Reverse name to reply Defocus information is neural, but local. I don't think that scientists have determined a central mechanism for myopiagenesis, the process of which also seems to have a definite endpoint in the mid- teens. Actually, there is evidence that it occurs in two phases, a rapid infantile phase, and a slower juvenile phase. DrG "Dr. Leukoma" <drg@leukoma.com> wrote in news:1173136616.843347.53130 @v33g2000cwv.googlegroups.com: > Actually, there is evidence that it occurs in two phases, a > rapid infantile phase, and a slower juvenile phase. So, if we'd want to draw parallels, we'd probably point to the chick data as more analogous to the rapid infantile stage?? SignatureScott Reverse name to reply > "Dr. Leukoma" <d...@leukoma.com> wrote in news:1173136616.843347.53130 > @v33g2000cwv.googlegroups.com: [quoted text clipped - 8 lines] > Scott > Reverse name to reply I'm not sure what the differences are in the mechanisms underlying the two phases, and so I can't comment. Like you, I believe that primate data would be more applicable to humans, but I think the question was provocative nevertheless: should we studiously avoid blurred images? DrG "Dr. Leukoma" <drg@leukoma.com> wrote in news:1173188561.537427.189180 @p10g2000cwp.googlegroups.com: > hould we studiously avoid blurred images? How can you studiously avoid blurred images? When you're focussed at near, distance is blurred, and when focussed far, near is blurred? So now, we need to studiously avoid blurred foveal images, based on research carried out during the developmental stage of a non foveate animal. SignatureScott Reverse name to reply > "Dr. Leukoma" <d...@leukoma.com> wrote in news:1173188561.537427.189180 > @p10g2000cwp.googlegroups.com: [quoted text clipped - 11 lines] > Scott > Reverse name to reply Regardless of the non-foveate studies, I think it's a fair question based upon foveate studies as well. In fact, not only do I think it's a fair question, I also think that the clinical implications are compelling. DrG |
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