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Science Forum Index » Medicine - Vision Forum » Difference in reading power of New Rx vs Old Rx
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| Mark A |
 Posted: Tue Jan 09, 2007 2:08 am |
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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). |
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| Mike Tyner |
| Posted: Tue Jan 09, 2007 2:16 am |
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"Mark A" <nobody@nowhere.com> wrote
Quote: 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 |
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| Mark A |
| Posted: Tue Jan 09, 2007 10:19 pm |
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Mike Tyner wrote:
Quote: 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 ? |
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| Mike Tyner |
| Posted: Wed Jan 10, 2007 8:21 am |
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Guest
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"Mark A" <m0002a@yahoo.com> wrote
Quote: 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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