Eyeglass Prescription Fluctuation

by Herb

Q: Is it normal for an eyeglass prescription to fluctuate as much as my prescriptions?

I have received 3 pairs of glasses over the past 7 years that I just can't see with properly, including my current pair (2013). One pair was confirmed to be a lab error and was replaced. I see fine with the pair from 2012 that I use as backups and while sailing.

After reviewing the prescriptions I have on hand, I see a lot a fluctuation. I have read what I can find on the internet about deciphering prescriptions and am wondering if my prescriptions are my problem. All glasses have been made by VBA. In particular, the Cylinder and Axis varying so much puzzles me.

I am due for another exam in 2 weeks and would like to know if the following looks normal or if I should go to another optometrist. 2008 was done by Dr. A, the rest by my current Dr. B. I had exams on the missing years and received new glasses, but wasn't provided with the prescriptions.

OD Sphere +0.25 Cylinder -0.50 Axis 17 Add +2.00
OS            +0.50             -0.50       156       +2.00

OD Sphere Plano Cylinder +0.50 Axis 175 Add +2.00
OS            +0.25            +0.25        025        +2.00

OD Sphere +0.50 Cylinder +0.25 Axis 010 Add +2.25
OS            +0.50             +0.25        180        +2.25

OD Sphere Plano Cylinder +0.50 Axis 160 Add +2.25
OS            +0.50            +0.50         025       +2.25

Thanks in advance!

A: I will start first by explaining that an eyeglass prescription that contains both spherical and cylinder can be written in 2 ways: with minus (-) cylinder or with plus (+) cylinder.

I will use your first pair of glasses to show you that it can be written like this:

1. OD : Sphere +0.25 Cylinder -0.50 Axis 17 Add +2.00
    OS              +0.50              -0.50      156        +2.00

2. OD Sphere -0.25 Cylinder +0.50 Axis 107 Add +2.00
    OS              0.00             +0.50         66        +2.00

These 2 ways even if look different, they are the same.

So, if you compare with the next pair, you will see that is no so much difference, is only 0.25 Sph.

The 0.25 Sph difference is considered normal, this small variation can occur when you go to the examination tired, for example. There are people who are not bothered by a 0.25 diopter balance and see the same with both glasses, but there are persons who can feel this small difference and see well only with the right pair. The right thing to do is to have a more detailed consultation, to try on different glasses with 0.25 diopters difference and choose the one that offers the best vision.

With the rest, you are right the cylinder and axis variations are not big but strange.

About the cylinder, I can tell you that the astigmatism is for life and does not heal, so a smaller cylinder is not right as was the transition from 2009 to 2013. As you said, the pair with the 0.25 cylinder is the best so far (as vision), so I wonder why they change it back to 0.50??

My opinion is that the right one is 0.25 cylinder, and it was from the beginning (the one you see best) and is not a good idea to change it specially if you had 0.50 cylinder before, and it was not ok.

And the axis…. I can understand a small variation of 1-2 degrees / 2-3 years, but this much I think is a refractometer measurement error. There are tests that find the perfect axis, and they must be done, not just trust the refractometer.

In the end, I think that if you have a clear vision with one pair of glasses, you don’t need to replace them. If you need another pair, make another one, but with the same diopters.

About the consultation, you should go to the same optometrist for changing the eyeglass prescription because he knows your problems best. But if he is wrong, you can always find another one.

If you have any questions, do comment and ask, please.

Hope this helps,

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