 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Medical Forum / General / Vision / February 2005?? Acuity <-> Diopters Conversion ??
I can find lots of web sites that tell me what 20/20, 20/60, 20/100 etc. mean. I also find lots of sites that explain diopters (d = 1/f) But how do I relate the two? e.g. if someone is -4.5 sph, is that 20/100, 20/200, or what? TIA As a non-professional I don't think they are necessarily related. My prescription is -2.5 but my bcva (best corrected visual acuity) is 20/40. However my underlying eye condition (CSNB) may make me the exception not the rule. Scott > I can find lots of web sites that tell me what 20/20, > 20/60, 20/100 etc. mean. [quoted text clipped - 6 lines] > > TIA >As a non-professional I don't think they are necessarily related. >My prescription is -2.5 but my bcva (best corrected visual acuity) is 20/40. >However my underlying eye condition (CSNB) may make me the exception not the >rule. Maybe I didn't describe it properly, but I am interested in *uncorrected* acuity. i.e. if -4.25 corrects the eyesight to 20/20, what is the acuity without the glasses? Is there a formula for this? Dear Joe, Subject: VA and "Diopters". There is no formula -- but the APPROXIMATE judgment is that if you are reading 20/70, a lens strength of from -3/4 to -1.5 diopters will clear the 20/20 line. This measurement is "critical" for light intensity. Some people can read the Snellen-DMV test at 20/30 and 20/40, (Pass) but in a darkened room using a "projected" Snellen will measure about -2.0 diopters using a phoropter (trial-lens) measurement system. Hope this clarifies the issue. Best, Otis Engineer One of the docs probably has some info on this, but I don't think it is a hard and fast formula. Of course, this assumes you want to know about minus diopters. If you're like me (currently +3.25, +2.25) you're more interested in the plus side of the equation. Up until 3 or 4 years ago (I'm 42 now) I could squint my way to passing the DMV test (though I had a very generous tester the last time - let me use two different methods, and took the results of the better) > (I'm 42 now) I could squint my way to passing the DMV test (though I > had a very generous tester the last time - let me use two different > methods, and took the results of the better) Is this a science? I thought that science was against tricks. But this forum is all about tricks that some cunning people is making against the gullible. > Maybe I didn't describe it properly, but I am interested in > *uncorrected* acuity. i.e. if -4.25 corrects the eyesight to > 20/20, what is the acuity without the glasses? Is there a > formula for this? Is there a formula that explains how your mind functions? > Maybe I didn't describe it properly, but I am interested > in *uncorrected* acuity. i.e. if -4.25 corrects the > eyesight to 20/20, what is the acuity without the > glasses? Is there a formula for this? There is a _rough_ correlation. Look up the "Dead Horse" formula discussed in this group a few years back. -- Robert > As a non-professional I don't think they are necessarily related. > My prescription is -2.5 but my bcva (best corrected visual acuity) is 20/40. > However my underlying eye condition (CSNB) may make me the exception not the > rule. Now see this learned man named Scott. He has a BCVA of only HALF of normal vision. He still believes in glasses!!! Is he really learned or just a stupid man who has just dropped any faith in his own intelligence? Dear Joe, If you wish to establish this relationship for yourself -- why not down-load a chart from www.i-see.org and read it? Why attempt a "formula" conversion. Roughly 20/70 is ABOUT 1.0 diopters. 70 x 4 = 20/280 -- as a rough guess It is better just to read the eye chart for yourself to establish this relationship. Otis Engineer >I can find lots of web sites that tell me what 20/20, >20/60, 20/100 etc. mean. [quoted text clipped - 6 lines] > >TIA Too many variables for a formula. I'd guess your uncorrected VA is 20/400 to 20/600 if your eyes are healthy. Hope this helps Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France For Joe: It would now be interesting to find out exactly what line you can read on the Snellen in a room with good illumination. Why not give it a shot and find out who is closer? Best, Otis > Too many variables for a formula. I'd guess your uncorrected VA is 20/400 to > 20/600 if your eyes are healthy. > > Hope this helps > Robert Martellaro Now look how this seller makes up a GREAT manipulation of data. How can an eye with 20/600 BE CALLED HEALTHY??? It is all a whole big trick played on the minds of the weaker. > I can find lots of web sites that tell me what 20/20, > 20/60, 20/100 etc. mean. [quoted text clipped - 4 lines] > > e.g. if someone is -4.5 sph, is that 20/100, 20/200, or what? The two measures are not related in a way that is predictable, uncorrected acuity depends not only on Rx but on light level, pupil size, lid squinting, your individual willingness to guess and your ability to deduce letters from there shape, test distance (whether 5 ft, 10 ft or 20 ft). If you want to know your unaided acuity, have it measured. With an Rx over -4, by rule of thumb, you likely have unaided acuity worse than 20/400. If you are hyperopic or have astigmatism, then rules of thumb don't work at all. BTW, despite Otis's claims, unaided acuity cannot be reliably used to predict refractive error either. Why did you want to know your unaided acuity? Dr Judy > The two measures are not related in a way that is predictable, uncorrected > acuity depends not only on Rx but on light level, pupil size, lid squinting, > your individual willingness to guess and your ability to deduce letters from > there shape, test distance (whether 5 ft, 10 ft or 20 ft). If you want to > know your unaided acuity, have it measured. With an Rx over -4, by rule of > thumb, you likely have unaided acuity worse than 20/400. NOW EXPLAIN PLEASE HOW CAN YOU PRESCRIBE THE RIGHT GLASSES GIVEN ALL THESE UNPREDICTABLE VARIABLES!!! > If you are hyperopic or have astigmatism, then rules of thumb don't work at > all. AND YOU CALL YOUR WORK A SCIENCE??? > BTW, despite Otis's claims, unaided acuity cannot be reliably used to > predict refractive error either. OTIS IS RIGHT, THE ONLY SOLUTION TO THE PROBLEM IS A MODEL IN WHICH THE EYE IS A DYNAMIC SYSTEM THAT SHIFTS HIS OWN POWER OF REFRACTION. To harness that system by the use of the mind is the whole Bates Discovery. http://TheCentralFixation.com >Why did you want to know your unaided acuity? I asked this question out of nothing more than idle curiosity. Please, let this thread die. It's not important. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.