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Medical Forum / General / Vision / March 2006Myopia vs eyeball length correlation?
As a nosey and troublesome "patient", I have rarely failed to ask the eye people, when the occasion arose, why do I need these unwieldy minus lenses(?). When forthcoming, the answer was, in so many words, because my eyeballs, for some mysterious reason that nobody can describe, by a similarly mysterious process, have undertaken to make themselves grow too long. Well, then, now that eyeball length is easily, and frequently, measured, as, for instance, by ultrasound, have there been done any studies to obtain the correlation of eyeball length with refractive error? Are there, for instance, any instances of emmetropia in deep eyeballs? Thanks in advance for any hints. -- Dicky dickd0tadamsatbigfootperi0dcom Test question: If the debt limit is $9 trillion, how much is it for each of 300 million of us? (Statistics show that 98% of Americans cannot answer this question. The rest simply do not want to know.) http://www.bloomberg.com/apps/news?pid=10000103&sid=a0g_foJfDQ0M&refer=us > As a nosey and troublesome "patient", I have rarely failed to ask the > eye people, when the occasion arose, why do I need these unwieldy > minus lenses(?). If you don't like them, don't wear them.  SignatureScott Reverse name to reply have there been done any studies > to obtain the correlation of eyeball length with refractive error? tons of them. > Are there, for instance, any instances of emmetropia in deep eyeballs? there are probably some. the longer the eye becomes, the flatter the cornea and/or the weaker the crystalline lens must be to remain emmetropic. the fact is, most emmetropic eyes are average axial length; most myopic eyes are longer than average; most hyperopic eyes are shorter than average. w.stacy, o.d. Yes Dick, there is a strong correlation between axial length and myopia. The average eyeball is around 20-25mm long. Some are longer and some shorter. A process we call emmetropisation occurs during infancy to the age of around 5yo when the eye is at its full adult size. The eyeball actively tries to be emmetropic (no prescription - actually +0.75D - and proper focus on the retina). This generally occurs regardless of the length of the eye. The corneal curve, lens power, axial length, anterior chamber depth and vitreous chamber depth all are components in the refractive status of the eye and overall power. When myopia occurs, the eyeball actually grows by roughly 1mm per 3D of myopia. When we look at mass studies, myopes have generally steeper corneas and longer axial lengths and hyperopes generally flatter corneas and shorter axial lengths. dr grant > When myopia occurs, the eyeball actually grows by roughly 1mm per 3D of > myopia. My lord, why does it do that? > When we look at mass studies, myopes have generally steeper corneas > and longer axial lengths and hyperopes generally flatter corneas and > shorter axial lengths. Thank you. Can you point me to the mass studies? Actually, I am in Mass., near Boston. Am I warm? -- Dicky Dear Dicky, Subject: The effect a minus has on the natural eye refractive state. When you place a minus lens on the monkey's eyes their refractive state move in the direction of the applied minus lens (say -3 diopters). For this proven fact to happen, (change of refractive state) a number of components of the eye's refractive system MUST CHANGE. They could be: 1. The eye "lengthens" slightly. (1mm for 3 diopter.) or 2. The cornea gets less "steep" or 3. A refractive index changes (less probable) or 4. All of the above. But the operative fact is that the naturel eye changes its refractive state as the "environment" is moved closer. Now one has yet been able to pin down which of the four above ACTUALLY changes -- it is just conjecture at this point. But it is a scientific fact that the natural primate eye does change in this manner -- as a dynamic system. Just one man's opinion. Best, Otis > Dear Dicky, > > Subject: The effect a minus has on the natural eye refractive > state. > > When you place a minus lens on the monkey's eyes May or may not be relevant. What's its effect on humans ... and remember: please cite your source. Thanks. emmetropic eyeball is 24mm, each mm longer is -2.5 diopters Dear Neil, In case you did not notice -- it is prohibited that scientific test on the human naturel eye are prohibited -- because they would cause "stair case" myopia if they were ever conducted. Therefore you must study the natural (dynamic) primate eye -- and draw your own conclusions about the naturl HUMAN PRIMATE EYE. That is why there is a preventive second-opnion, since these issues of technical analysis CAN NEVER BE RESOLVED. Best, Otis > Dear Neil, > [quoted text clipped - 3 lines] > "stair case" myopia if they were ever > conducted. Without taking the time to complement you on your brilliant literary style there .... What about *retrospective* studies using humans. Shouldn't be that tough. > Therefore you must study the natural (dynamic) > primate eye -- and draw your own conclusions > about the naturl HUMAN PRIMATE EYE. But I've posted the citations that discuss the differences between those world-famous monkey and chicken eyes that so fascinate you and the human eyes that ... well ... really matter to most of us. How do you reconcile that gap? > > Dear Neil, > > [quoted text clipped - 19 lines] > > How do you reconcile that gap? Otis?? >> > Dear Neil, >> > [quoted text clipped - 9 lines] >> What about *retrospective* studies using humans. Shouldn't be that >> tough. Uncle Otie? Aren't you going to answer this simple, direct question?? >> > Therefore you must study the natural (dynamic) >> > primate eye -- and draw your own conclusions [quoted text clipped - 7 lines] > >Otis?? Uncle Otie? Aren't you going to answer this simple, direct question?? Okay, jumping back into the game. So monkeys and chickens are given -3 lenses to wear and they develop myopia. Was their manifest refraction -3 at the time they were given these lenses (by the way, do you have pictures of these chickens wearing glasses?) Who puts -3 lenses on anyone who doesn't need -3 correction? How does logic follow that putting -3 lenses on chickens that don't have any refractive error will cause myopia in humans who have refractive error? Signature~RT > In case you did not notice -- it is prohibited that > scientific test on the human naturel eye are > prohibited -- because they would cause > "stair case" myopia if they were ever > conducted. Nonsense. What's "prohibited" about comparing those who wear glasses with those who don't? Why would you ignore the results when those comparisons are made? > That is why there is a preventive second-opnion, > since these issues of technical analysis > CAN NEVER BE RESOLVED. In your dreams. -MT > What's "prohibited" about comparing those who wear glasses with those who > don't? I get it now, Otis's oft cited study is about putting minus lenses on animals with no refractive error. In that case I believe that the eye would adapt by becoming myopic--to see in order to survive. It has nothing to do with CORRECTING a refractive error. Signature~RT > In that case I believe that the eye would adapt by becoming myopic--to > see in order to survive. Just to clarify, I believe that chicken eyes would adapt because, as we all know, they have very complex visual needs. they found that being myopic was actually quite helpful when scratching for grubs. Signature~RT |
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