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Medical Forum / General / Vision / April 2007my son's vision
my son's vision diagnosis was OD: -2.00 + 0.50 x 180 OS: -2.00 sph What does this mean in general? And would this be considered a Negative 2.5, 3.5, etc? I am looking into buying my son goggles with a somewhat corrective lense and I am not sure what to look for to best suit him. THANK YOU!! > my son's vision diagnosis was OD: -2.00 + 0.50 x 180 > OS: -2.00 sph [quoted text clipped - 5 lines] > > THANK YOU!! This means your son is short-sighted or myopic. If you are buying swimming goggles then the closest equivalent would be R either -1.50 or -1.75 L -2.00 Dom Dom, it looks like you've subtracted the +0.50 from the -2 to get a -1.50 or - 1.75. Does that mean then that if someone has a minus prescription with plus cyl that it makes it less strong than a minus prescription with minus cyl? What if I'm -2.50 with -0.50 and my friend is -2.50 with +0.50, whose vision is worse without glasses? Is that 0.50 significant enough to make a big difference? > Dom, it looks like you've subtracted the +0.50 from the -2 to get a -1.50 or - > 1.75. > Does that mean then that if someone has a minus prescription with plus cyl > that it makes it less strong than a minus prescription with minus cyl? What > if I'm -2.50 with -0.50 and my friend is -2.50 with +0.50, whose vision is > worse without glasses? I join this question. I have noticed that there are 2 ways of writing the same Rx for myopia (I am not familiar with other kinds of Rx, so my question is limited to myopia with astigmatism). It seems to me that the 2 following Rx examples are idintical: #1. Sphere: -3.00 Cyl: -1.00 #2. Sphere: -4.00 Cyl: +1.00 Mathematically speaking it doesn't make much sense, since -3-1=-4, whereas -4+1=-3, thus the prescriptions are not equal, but I believe that in the optomeric world they are. Am I correct? Moreover, would you say that this person refractive correction (I hope I am using the proper term) is -3 or -4? > > Dom, it looks like you've subtracted the +0.50 from the -2 to get a -1.50 or - > > 1.75. [quoted text clipped - 14 lines] > whereas -4+1=-3, thus the prescriptions are not equal, but I believe > that in the optomeric world they are. Am I correct? # 1 means you are -3 in one meridian and -4 in the other # 2 means you are -4 in one meridian and -3 in the other So exactly equivalent. > Moreover, would you say that this person refractive correction (I hope > I am using the proper term) is -3 or -4? You say they are -4.00 +1.00 or you say they are -3.00 -1.00. Incorrect to use only the sphere and not the cyl. Or you can calculate equivalent sphere, in which #1 gives: -3.00 + (-1/2) = -3.50 #2 gives: -4.00 + (+1/2) = -3.50 Dr Judy > #1. Sphere: -3.00 Cyl: -1.00 > #2. Sphere: -4.00 Cyl: +1.00 > > Mathematically speaking it doesn't make much sense, since -3-1=-4, > whereas -4+1=-3, thus the prescriptions are not equal, but I believe > that in the optomeric world they are. Am I correct? Yes. One meridian (eg vertical) is -3.00. The other meridian (horiz) is -4.00. You can describe this as -300-100, or -400+100. The key is the third number you didn't list. If the first rx (in "minus cylinder form") says axis 90, the second version ("plus cyl") is axis 180. In the optometric world, 90 is the opposite of 180. > Moreover, would you say that this person refractive correction (I hope > I am using the proper term) is -3 or -4? The concept of "spherical equivalent" averages the -3 and -4 meridians to a spherical -3.50. That's a fair measure of how nearsighted, overall. -MT > > #1. Sphere: -3.00 Cyl: -1.00 > > #2. Sphere: -4.00 Cyl: +1.00 [quoted text clipped - 18 lines] > > -MT Wow! I have a master degree in math, but this optometric math is something else! Maybe I should consider it for a Ph.D. subject, LOL! Anyway, you Mike, Dr Judy and the others are very helpful in clearing up some of the confusion we common folks have. Thanks! >>> #1. Sphere: -3.00 Cyl: -1.00 >>> #2. Sphere: -4.00 Cyl: +1.00 [quoted text clipped - 18 lines] > Wow! I have a master degree in math, but this optometric math is > something else! Maybe I should consider it for a Ph.D. subject, LOL! As another non-optometrist, with some optics background, it was puzzling to me, too. I see the sense of it now, with the cylinder essentially accounting for 1/2 strength when approximated as a sphere - it only refracts on one axis. The 90/180 degree being "opposites" is strange, but again, it makes sense when (if I understood correctly!) you say a positive cylinder at 90 is similar to a negative cylinder at 180. Both would have a similar effect on the observed aspect ratio - squashing one axis or stretching the complementary one... Dave > As another non-optometrist, with some optics background, it was puzzling > to me, too. I see the sense of it now, with the cylinder essentially [quoted text clipped - 5 lines] > effect on the observed aspect ratio - squashing one axis or stretching > the complementary one... I am glad that Dave finds the sense in the "spherical equivalent", but I am still puzzled... Adding (or subtracting, which seems to be the same thing in optometric math) sphere and cylinder measurements appers to me like adding (or subtracting) apples and oranges. My understanding is that this "math" is an effort to express roughly the refractive correction in one number. Is it? This interests me not only from a mathematical POV, but also personally, since I am facing a cataract surgery in my right eye (my bad eye). I have been told that a disparity between the eyes (or the correction? not sure) should not be more than 2D, but I have no idea what this "2D" represents, and on the top of it I now don't even know whether it's the "spherical equivalent" or simply the sphere. I will present my troubling personal problem (and confusion) in a new thread, perhaps tomorrow -- too late now. > I am glad that Dave finds the sense in the "spherical equivalent", but > I am still puzzled... Adding (or subtracting, which seems to be the > same thing in optometric math) sphere and cylinder measurements appers > to me like adding (or subtracting) apples and oranges. My > understanding is that this "math" is an effort to express roughly the > refractive correction in one number. Is it? The sphere/cyl method of specifying Rx is shorthand and leads you to think we are comparing apples and oranges. If, instead of specifying one meridian as more or less power than the other, we specified each separately, you might understand equivalent sphere better. So for your -3.00 -1.00 or -4.00 +1.00 case: Specify fully: -3.00 axis 180 with -4.00 axis 90. Notice we don't use the word sphere or cyl, we simply specify the actual power along a meridian. The equivalent sphere is then the average of the two meridians: (-3.00 + -4.00)/ 2 = -3.50 > This interests me not only from a mathematical POV, but also > personally, since I am facing a cataract surgery in my right eye (my > bad eye). I have been told that a disparity between the eyes (or the > correction? not sure) should not be more than 2D, but I have no idea > what this "2D" represents, and on the top of it I now don't even know > whether it's the "spherical equivalent" or simply the sphere. Spherical equivalent is the measure if you are concerned about the difference between the two eyes. However, with cataract surgery it is only a temporary problem that can be managed with slab off prism if the eyes are different. When the second eye is done then the difference will be eliminated. Don't worry. > Dom, it looks like you've subtracted the +0.50 from the -2 to get a -1.50 or - > 1.75. [quoted text clipped - 3 lines] > worse without glasses? Is that 0.50 significant enough to make a big > difference? It means you are -2.50 in one meridian and -3.00 in the other; your friend is -2.00 in one meridian and -2.50 in the other. So likely your vision is worse without glasses but not by much. Not a big difference. Dr Judy > -- > Message posted viahttp://www.medkb.com >my son's vision diagnosis was OD: -2.00 + 0.50 x 180 >OS: -2.00 sph [quoted text clipped - 5 lines] > >THANK YOU!! http://www.tedmontgomery.com/the_eye/glasses.html Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman |
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