Difference in Prescription

by Mary
(Louisville)

A:Hi - I have a new prescription that seems very different than my 3-year old one.

OLD
SPH CYL AXIS ADD
O.D. (right) 0.75 -0.5 180 2.5
O.S. (left) 2 -0.5 180 2.5

NEW
SPH CYL AXIS ADD
O.D. (right) 1 0.25 90 2.75
O.S. (left) 1.75 0.75 90 2.75



A: Hello Mary,

As you are known, you have astigmatism, and your lenses have two components: spherical and cylinder.

The thing is that an astigmatism prescription can be written 2 ways: one is with -cylinder and one with +cylinder.

They look different, but they are the same. I will take as an example your prescription and convert it both ways so you can see the differences.

So, your old prescription looks like this:

+0.75 sph and -0.50 Cyl 180 degrees.

If I convert this in +cylinder, it will be:

+0.25 sph and +0.50 Cyl 90 degrees.

These two are the same. So if you look to your new prescription (also written with +cylinder) you will see that the differences are small.

Same with the left eye:

Old:
+2.00 sph and -0.50 Cyl 180 degrees is same with...

+1.50 sph and +0.50 Cyl 90 degrees

There are differences with the new prescription, but they are small differences.

Hope this helps,
Arpi

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