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Medical Forum / General / Vision / October 2006eye math question
Recently I have noticed that my vision was not quite as sharp at a distance. Based on this group, I have tried using the plus lens for close work in hopes to improve the crispness of my distance vision. After using the plus lenes for about a month, here is what I have found: With +1.25 lens if I start out close and move away from an object, it starts to blur at the following distance: Left Eye: 21" Right Eye: 26" Prior to using the plus lenes for close work here were my measurements. Left Eye: 19" Right Eye: 22" I don't know the math, but believe it should be possible to calculate an approxamite D value. I want to compare the before and after. I'm not intested in a discussion about plus lenses, just in the math. How much worse is my left eye than my right eye? > Recently I have noticed that my vision was not quite as sharp at a distance. > Based on this group, I have tried using the plus lens for close work in [quoted text clipped - 17 lines] > > How much worse is my left eye than my right eye? 42  SignatureDan Abel dabel@sonic.net Petaluma, California, USA Dear Dennis, The baisc equation for distance to diopters is: Diopters = 1/ focal-distance Thus a plus with a focal length of 1 meter will have a power of 1 diopter. A focal length of 1/2 meter, a power of 2 diopters. Using your distance method, and assuming a refractive state of zero for you: > With +1.25 lens if I start out close and move away from an object, it starts > to blur at the following distance: > > Prior to using the plus lenes for close work here were my measurements. > Left Eye: 19" 39.4 / 19 = 2.07 diopters > Right Eye: 22" 22 / 39.4 = 1.8 diopters Change in power after wearing a +1.25 diopter lens. > Left Eye: 21" 39.4 / 21 = 1.87 diopters > Right Eye: 26" 39.4 / 26 = 1.51 diopters. If you were consistent, then your refractive STATE changed SLIGHTLY in a positive direction. I am certain you will get some more commentary on this one. Best, Otis > Recently I have noticed that my vision was not quite as sharp at a distance. > Based on this group, I have tried using the plus lens for close work in [quoted text clipped - 17 lines] > > How much worse is my left eye than my right eye? > If you were consistent, then your refractive STATE changed > SLIGHTLY in a positive direction. Do you suppose his eyes got shorter? -MT > Do you suppose his eyes got shorter? > > -MT Shorter!?! Not noticeably by looking in the mirror! It must be changes in the muscles that focus the eyes. My vision has always varied quite a bit day-to-day. After extended close up work I have always noticed worse vision at distance. My guess is the using the plus lenses reduces my level of eyestrain during extended near work. Even time of day makes a difference. I have always seen sharper in the morining. Again I would attribute this to eyestrain. I also have worse vision when it is rainy than sunny. My theory is the variation in barometric pressure causes the eye to expand or contract. Anyone with other theories to explain this? > I also have worse vision when it is rainy than sunny. My theory is the > variation in barometric pressure causes the eye to expand or contract. > Anyone with other theories to explain this? That's good one!! I assume you're not being serious. Rather it has to do with lighting and illumination levels. frank Dennis <dennis@nospam.net> wrote in part: > I also have worse vision when it is rainy than sunny. > My theory is the variation in barometric pressure causes > the eye to expand or contract. Anyone with other theories > to explain this? Sure, it's simple optics that even "He Who Must Not Be Named" [elevator engineer] could understand: the aperature effect from the iris being open wider during low-light. There are also contrast effects if you like MTF. -- Robert On 10/11/06 10:45 AM, in article _4aXg.13961$6S3.8016@newssvr25.news.prodigy.net, "Robert Redelmeier" <redelm@ev1.net.invalid> wrote: > Dennis <dennis@nospam.net> wrote in part: >> I also have worse vision when it is rainy than sunny. [quoted text clipped - 8 lines] > > -- Robert Don't forget the drops that run across your lenses. ;=) -- Fermez le Bush Keep using those plus glasses to clear your refractive state to plano else you may develop stair-case myopia > Keep using those plus glasses to clear your refractive state to plano > else you may develop stair-case myopia So, you found a study that shows staircase myopia exists? I haven't. -MT > > Keep using those plus glasses to clear your refractive state to plano > > else you may develop stair-case myopia > > So, you found a study that shows staircase myopia exists? I haven't. > > -MT It was the "escaltor" study, it had pictures. Dear Ace, Mike> So, you found a study that shows staircase myopia exists? I haven't. Otis> That is because he chooses to ignore studies that show the effect. The Oakley-Young study showed that the kids with full-strength minus went DOWN at a rate of -2 diopters in four years. The "plus" group went down by approximagely zero diopters in those for years. I would call "down" at a steady -1/2 diopter per year "stair-case" myopia. Majority-opinion Mike, denies it. Make your own judgment accordingly. Best, Otis > > Keep using those plus glasses to clear your refractive state to plano > > else you may develop stair-case myopia > > So, you found a study that shows staircase myopia exists? I haven't. > > -MT > Dear Ace, > [quoted text clipped - 9 lines] > The "plus" group went down by approximagely zero diopters > in those for years. Still lying about Oakley-Young, huh, Otis?? You off the meds again? Dear Ace, Subject: Induced Stair-case myopia (from a minus lens) I would suggest reading: http://www.geocities.com/soonicansee/ For a graphic picture of the results produced by the Oakley-Young study. Best, Otis > Keep using those plus glasses to clear your refractive state to plano > else you may develop stair-case myopia Dear Ace, The natural eye's refractive STATE follows that minus lens. A great "graphic" of this can be found at: http://vision.berkeley.edu/wildsoet/myopiaprimer.html Thus stair-case myopia develops in these steps. 1. The kid has his nose almost on the book -- reading at -6 to -10 diopters. (6 inches to 4 inches). If he did this for short times -- no problems. But long hourse, and the eye adjusts its refractive STATE in a negative direction. (As a natural process.) 2. After a year or two of this, the refractive state changes from +1/4 to -1.0 diopters -- and a Snellen of 20/60. 3. Now, the kid gets a strong minus. The kid goes back to reading at -10 diopters, with the strong minus, and that "animation" shows how the natural eye "adapts" to BOTH the "near" AND the minus. 4. Thus the term, stair-case myopia. The majority-opinion says this "does not happen". The second-opinion says it does. You be the judge. Best, Otis > Keep using those plus glasses to clear your refractive state to plano > else you may develop stair-case myopia > Dear Ace, > [quoted text clipped - 36 lines] > > Keep using those plus glasses to clear your refractive state to plano > > else you may develop stair-case myopia Ive seen children read with their wretched minus on. Its no wonder why so many people are myopes, some in the double digits even! Im hoping for a brave new world where second opinion optometrists come in control and prevent the myopia epidemic what is today. Lasik is useless. Prevent myopia, dont go around ruining eyes with glasses than lasik! > > Do you suppose his eyes got shorter? > > [quoted text clipped - 6 lines] > work I have always noticed worse vision at distance. My guess is the using > the plus lenses reduces my level of eyestrain during extended near work. It is not uncommon for people to, following a long period of near work, to have a small, short acting spasm of the ciliary muscle (only one, not a multiple) that controls the focus of the lens inside the eye. Reading without your glasses would mean that the ciliary muscle is not in use so the plus may not be needed if you simply read with glasses off. Reading with a +1.25 if you are already about a -2 myope means you will need to hold things at about 30cm when reading with the plus. This will mean that the muscles that control convergence will be working overtime and may contribute to feelings of eye strain, headache, double vision and could cause blur. > Even time of day makes a difference. I have always seen sharper in the > morining. Again I would attribute this to eyestrain. Likely your ciliary muscle is relaxed in the mornings. > I also have worse vision when it is rainy than sunny. My theory is the > variation in barometric pressure causes the eye to expand or contract. Barometric pressure will not cause changes in eye size. Some people get migraine with pressure change and it can cause blurred vision. Or the dimmer light on cloudy days makes your pupil larger and vision worse. Dear Dennis, I also have worse vision when it is rainy than sunny. Otis> This is because of a characteristic of a camera called variously, "depth-of-field" or "depth-of-focus". In a camera, if you "stop-down" the aperture, to 2 mm, (say), the depth-of-field can increase by a diopter or so. In sun light, the eye automatically does this. Thus your Snellen would be clear on a bright day. At dusk, your aperture "opens up" to 7 or 8 mm, and your depth-of-focus can reduce to perhaps 1/2 to 2/4 diopters. My theory is the variation in barometric pressure causes the eye to expand or contract. Anyone with other theories to explain this? Otis> Depth-of-focus effects. If you used a "pin-hole" your visual acuity could be 20/20 because of that effect. Best, Otis > > Do you suppose his eyes got shorter? > > [quoted text clipped - 13 lines] > variation in barometric pressure causes the eye to expand or contract. > Anyone with other theories to explain this? > Dear Dennis, > > I also have worse vision when it is rainy than sunny. So does everyone else on this planet. > My theory is the > variation in barometric pressure causes the eye to expand or contract. No wonder people on this board consider you a moron. > Anyone with other theories to explain this? Yeah, LIGHT. Dear Dennis, Subject: Some more math, and estimating your refraction on the values you provided. If you had a refractive STATE of zero, and 20/20 -- you would be considered NORMAL. This is an analogy to the "camera" concept developed by Donders, Helmholtz and others. Using this concept we can estimate the following. +++++++++++++++++++ If you read at 20 inches (assuming you are young), it takes a change of +2 diopters to read at 20 inches. If you put a +1 diopter, you could read clearly at 20 inches. With a +2 diopter lens on, letters would still see clearly at 20 inches -- but not beyond. Since your "blur" starts with +1.25 diopter lens, it is possible to conclude that your refractive STATE must be on the order of -1 diopters. This would correspond to a Snellen of from 20/40 to 20/60. Best, Otis > Recently I have noticed that my vision was not quite as sharp at a distance. > Based on this group, I have tried using the plus lens for close work in [quoted text clipped - 17 lines] > > How much worse is my left eye than my right eye? otisbrown@pa.net schreef: > Dear Dennis, > [quoted text clipped - 3 lines] > If you had a refractive STATE of zero, and 20/20 -- you would > be considered NORMAL. Normal? Maybe the eye is emmetropic (no refraction error in the optical system while the eye is not accommodating and looking far away) Meanwhile it is possible the eye is one way or another just abnormal instead of normal. You are a real abnormal person Otis and your shortsightedness has nothing to do with this condition. > This is an analogy to the "camera" concept developed by Donders, > Helmholtz > and others. Ah, Otis starting to beat a retreat seeing the words "and others" and by his use of the word "camera" instead of his regular falsely stated term " fixed box camera" I should say, it is a start. He knows he is a liar and a charlatan. He never have read what Donders and von Helmholtz really did say about the eye. Free to Marcus Porcius Cato's "Ceterum censeo Carthaginem esse delendam" In conclusion, I think that the "old plus lens junk recovered by Otis" should be destroyed. Jan (normally Dutch spoken) otisbrown@pa.net schreef: > Dear Dennis, > [quoted text clipped - 3 lines] > If you had a refractive STATE of zero, and 20/20 -- you would > be considered NORMAL. Normal? Maybe the eye is emmetropic (no refraction error in the optical system while the eye is not accommodating and looking far away) Meanwhile it is possible the eye is one way or another just abnormal instead of normal. You are a real abnormal person Otis and your shortsightedness has nothing to do with this condition. > This is an analogy to the "camera" concept developed by Donders, > Helmholtz > and others. Ah, Otis starting to beat a retreat seeing the words "and others" and by his use of the word "camera" instead of his regular falsely stated term " fixed box camera" I should say, it is a start. He knows he is a liar and a charlatan. He never has read what Donders and von Helmholtz really did say about the eye. Free to Marcus Porcius Cato's "Ceterum censeo Carthaginem esse delendam" In conclusion, I think that the "old plus lens junk recovered by Otis" should be destroyed. Jan (normally Dutch spoken) |
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