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Medical Forum / General / Vision / January 2007Difference in reading power of New Rx vs Old Rx
I just received my new Rx and I am trying to figure out how much difference there is from my old one, especially in the reading area. I am concerned about this because I have found that over the 50 years that I worn glasses, that many ODs and OMDs tend to over-prescribe my hyperopia. This is especially problematic for progressives. Note that OD and OS are exactly the same because of amblyopia in right eye. Two different OD's did the refraction 3 years apart. Old Rx OD +4.25 -1.00 x 90 OS +4.25 -1.00 x 90 Add +2.00 New Rx OD +4.75 -1.75 x 90 OS +4.75 -1.75 x 90 Add +2.25 Question--Is the reading power in the New Rx +.75 diopter stronger than the Old Rx (increase of +.50 in sphere and +.25 in Add), or is this offset somewhat by the -.50 higher cyl (-1.75 vs 1.25) in the new Rx? Along the same lines as above, what is real difference in the distance power (does some of the increase in minus cyl offset the increase in sphere). > Along the same lines as above, what is real difference in the distance > power (does some of the increase in minus cyl offset the increase in > sphere). Yes. Use the rule of spherical equivalent and you find it's just a little more plus, overall. SE = sph + (cyl/2) -MT > Yes. Use the rule of spherical equivalent and you find it's just a little > more plus, overall. > > SE = sph + (cyl/2) > > -MT What about the reading power? Is it +4.75 + 2.25 (+7.00)? Or is it also reduced somewhat by the -1.75 cyl ? > What about the reading power? Is it +4.75 + 2.25 (+7.00)? Or is it > also reduced somewhat by the -1.75 cyl ? OD +4.25 -1.00 x 90 SE = +3.75 OD +4.75 -1.75 x 90 SE = +3.87 So the _distance_ Rx increases by 0.12. The additional 0.25 in the reading portion gets superimposed, bringing the total increase at _near_ to 0.37. The nominal reading distance would change from about 22" to 18", typical for someone in their late 40s or early 50s. -MT |
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