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Medical Forum / General / Vision / July 2004LASIK and high altitude
I recently completed an extensive training course on backcountry medical issues and the instructor said there was a "new" study that people who had LASIK were at much greater risk of a multitude of physical eye issues at altitude (above 8,000 feet for days/weeks). This would be in a mountaineering/trekking sort of sense; being in the Andes or the Himalayas for days or weeks at significantly higher altitude than the person normally lived at. I seem to remember something like that for RK and altitude changed the shape of the eye/lens/, but was under the impression that LASIK removed very little material and the physical integrity of the eye remains basically identical. Has anyone seen a study of LASIK at altitude? If so, can you provide me with a publication, date, etc.? Thanks much. Keith slim_westrum(no)@yahoo.com Remove '(no)' to get to me. > I recently completed an extensive training course on backcountry > medical issues and the instructor said there was a "new" study that [quoted text clipped - 16 lines] > Keith > slim_westrum(no)@yahoo.com Remove '(no)' to get to me. Here are three citations: Boes DA, Omura AK, Hennessy MJ Effect of high-altitude exposure on myopic laser in situ keratomileusis. J Cataract Refract Surg (United States), Dec 2001, 27(12) p1937-41 White LJ, Mader TH Refractive changes at high altitude after LASIK. Ophthalmology (United States), Dec 2000, 107(12) p2118 Dimmig JW, Tabin G The ascent of Mount Everest following laser in situ keratomileusis. J Refract Surg (United States), Jan-Feb 2003, 19(1) p48-51 DrG > Here are three citations: > [quoted text clipped - 11 lines] > > DrG Hallo Doctor G. Why don't you make a summary and tell us the juice of them? Perhaps the eyeball is not so "fixed" in its shape and may change, probably at high frequency, so to adjust in an instant to the variability of focus needed to see objects at different distance. For example, a perfect sighted person requires a very very short time to focus from infinity to two feet, isn't it true? It cannot be the action of the ciliary muscle. It must be the length of the eye that changes, many times per second in a vibration, and mind gets the signals from the retina only once in a while, as of in a sampling process. It gets only the image when the eye is at focus and discards the other images when the eye is adjusting. This process should be very very quick, perhaps more than double the 25 times per second we need when we watch TV or the movies. A myopic person, hence, has this range of axial lengths out of shape, the average size is too high. An hypermetropic person just the reverse, the eye oscillates around an average number which is too short. This explains why people at the beginning of treatment by rest methods, after discarding the glasses forever, have flashes of perfect sight very very easily: they report that there is no time passing from a state of high myopia to normal emmetropic eye. It seems it happens that the eye for a few seconda has shifted a bit the range of oscillation and mind has got a clear image in the sampling process. If there are people interested in this kind of stuff, please contact me at http://thecentralfixation.com > It must be the length of the eye that changes, many times per second > in a vibration, and mind gets the signals from the retina only once in > a while, as of in a sampling process. It gets only the image when the > eye is at focus and discards the other images when the eye is > adjusting. This process should be very very quick, perhaps more than > double the 25 times per second we need when we watch TV or the movies. So THAT explains the buzzing in my head! It would be interesting to hear how eyes vibrate without somebody feeling it or seeing it or measuring it. Actually, in the US it's 30 Hz (well, 29.97). In Europe it's 25. When we go over there, we have to use a converter or our vision flipflops terribly. -MT > Actually, in the US it's 30 Hz (well, 29.97). In Europe it's 25. When we go > over there, we have to use a converter or our vision flipflops terribly. Oh, so _that's_ why metric hurtz! :) Pity the Japanese -- they've got both power frequencies in the same country, on the same island! Small wonder they need glasses more than the rest of us! :) Maybe Rishi just uses DC voltage? -- Robert > > Actually, in the US it's 30 Hz (well, 29.97). In Europe it's 25. When we go > > over there, we have to use a converter or our vision flipflops terribly. [quoted text clipped - 4 lines] > the same country, on the same island! Small wonder they > need glasses more than the rest of us! :) Indecision must be some sort of national trait -- there used to be two flavors of metric bolts -- normal and Japanese. Perhaps they stopped that, but it was a real nuisance for a while. > Maybe Rishi just uses DC voltage? On the net, nobody can see the electrodes in your neck.  SignatureCheers, Bev * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do not try to solve all life's problems at once -- learn to dread each day as it comes. -- Donald Kaul >Robert Redelmeier redelm@ev1.net.invalid Writes: >> Actually, in the US it's 30 Hz (well, 29.97). In Europe it's 25. When we go >> over there, we have to use a converter or our vision flipflops terribly. [quoted text clipped - 6 lines] > >Maybe Rishi just uses DC voltage? Perhaps Rishi uses DC voltage . But judging from his posts, it seems likely that he has been Westinghoused at least once. I put my money on AC for Rishi. > Perhaps Rishi uses DC voltage . But judging from his posts, it seems likely > that he has been Westinghoused at least once. I put my money on AC for Rishi. You win, but who's gonna pay you? Do you wear glasses? > > It must be the length of the eye that changes, many times per second > > in a vibration, and mind gets the signals from the retina only once in [quoted text clipped - 12 lines] > > -MT Dear Friends, The eye does show a steady "tremmor", or "movement". At first this was thought to be "noise in the sytem", but later research demonstrated that when this movement was "supressed", the retinal image would "fade", and "distort" in various ways. Later ("The Silicon Retina" -- I believe) the research showed that the retina as a "network" REQUIRED the movement inorder to detect edges -- and this process was essential for control of the accommodation sytem. The "Rishi" might not be saying it "correctly", but the "vision" as a rock steady device with no active movement is not correct. Best, Otis Engineer > The eye does show a steady "tremmor", or "movement". > > At first this was thought to be "noise in the sytem", > but later research demonstrated that when this > movement was "supressed", the retinal image > would "fade", and "distort" in various ways. But that's nothing to do with focus. You're describing x and y motion, microsaccades, drift, and tremor. Rishi says the eye grows shorter and longer along the z axis, with axial length varying at 25 Hz, back and forth in your "deadband" to maintain focus. TC on the order of 0.002 seconds, if you prefer. I'm asking why we can't feel it. Do you know? In fact focus _does_ vary focus back and forth a little, but it isn't a regular sinusoid and it isn't 25 hz and it isn't accompanied by change in axial length. > The "Rishi" might not be saying it "correctly", > but the "vision" as a rock steady device with > no active movement is not correct. Glad you could shed light on that. Rishi is grabbing an opportunity to preach Bates - the ciliary and lens aren't responsible for accommodation, it must be something else. Ultrasound images lie. Doesn't it just make you cringe when laymen lecture from slipshod understanding, when mythology is pronounced as fact? -MT |
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