If they numbers are so different now, why can I still see?

December 27, 2012 11:21 AM

Does this eye glasses prescription look right? Significant difference between my old prescription, which I'm still using and work fine, and my new prescription - including a switch from - to + on some numbers. Specifics are inside.

After my recent eye exam (specifically for contacts) I asked for an updated glasses prescription as well, since I'd lost my old numbers. My old glasses are about two years old and still seem to work fine. After getting my new prescription, I found my old prescription.

I'm planning on ordering two pairs of glasses to use up my remaining FSA money before the end of the year, but the significant difference in the numbers is giving me pause. I've left a message with my optometrist's office to confirm the numbers, but thought I'd ask here to see if maybe I just don't understand what the numbers are telling me :)

Old Numbers:
O.D. +1.25 +4.00 005
O.S. -0.25 +1.75 180

New Numbers:
O.D. +5.00 -4.00 90
O.S. +1.50 -1.75 88


Does this switch seem reasonable? I'm suspicious that maybe the second column of numbers in the new prescription were mistakenly written as a - instead of a + since they're the same numbers as before, just with the sign changed. Do the other changes account for this sign change? Thanks!

posted by Arbac to health & fitness (11 answers total)

IANAO but yeah, that seems nutty to me. I can also attest to how often my own script gets messed up along the way from Dr to Dr to Eyewear place etc. I have to watch them like a (half-blind) hawk.
posted by Cosine at 11:26 AM on December 27, 2012

You can't say whether the change makes sense like that since they're written in two different formats. The old numbers are describing the power along a different meridian than the new numbers which is why the sign flipped. I'd be more surprised at the change in the spherical numbers. You say your old glasses work fine but the new lenses are 4-6x stronger than the old lenses. That's a significant change!

Are you certain you just don't know what good vision looks like any more? Because you should notice a very big difference between +1.25 and +5.00.
posted by Justinian at 11:38 AM on December 27, 2012

I was given a bad Rx once from a similar shift in strength, which resulted in a bad pair of glasses. Get your Rx checked a second time.
posted by Blazecock Pileon at 11:43 AM on December 27, 2012

Possibly relevant Wikipedia article

Basically, prescriptions are weird. Nothing wrong with verifying.
posted by yohko at 11:46 AM on December 27, 2012

Seconding the second opinion. Nothing worse than an incorrect prescription and you'd have noted such a huge jump in value in your vision.
posted by infini at 11:55 AM on December 27, 2012

Thanks for the info - after doing the conversion from plus notation to minus notation mentioned in the wiki article, it looks like the numbers are pretty similar. I got the method for conversion for future reference from here

From the wiki: "In practice, optometrists tend to use minus-cylinder notation, whereas ophthalmologists and orthoptists tend to prescribe using plus-cylinder notation."

This makes a lot of sense now - my old numbers came from an ophthalmologist and the new ones from an optometrist. Who knew!? I'll still wait for a call-back confirming the numbers before purchasing anything, but I understand the difference in numbers now.
posted by Arbac at 12:00 PM on December 27, 2012

Definitely double-check. I once had an optometrist from a chain remove my astigmatism correction without telling me. The resulting glasses were criminally bad.
posted by Thorzdad at 12:05 PM on December 27, 2012

Double-check, just to be sure. I had glasses that went from +2 to +4. They made them wrong (mis-read the number) and I had a headache for two months before I realized what the problem was (when the lens in my good eye fell out and I couldn't see a blasted thing!)
posted by Ruthless Bunny at 12:38 PM on December 27, 2012

Previously on AskMe about the astigmatism (cylindrical) correction...it's the opposite sign but also rotated by about 90 degrees, so it is functionally the same.

That said, I would be crazy worried about the change in spherical correction, from +1.25 to +5 is a huge jump. Even if it's correct, your eyesight deteriorating that quickly is cause for checking it out further.
posted by anaelith at 12:55 PM on December 27, 2012

That said, I would be crazy worried about the change in spherical correction, from +1.25 to +5 is a huge jump. Even if it's correct, your eyesight deteriorating that quickly is cause for checking it out further.

It's not actually all that much of a change. It's just written in a different format. One format says "Make the whole lens +1.25 and then add a +4.00 astigmatism correction at 5 degrees." The other says "make the whole lens +5.00 and subtract -4.00 astigmatism correction at 90 degrees." It's functionally the same (+4 correction measured at vertical, +1 correction at the horizontal), except that the new one adds .25 power and shifts the angle of the correction by 5 degrees. That's within normal error margins, and/or normal eye changes.
posted by gjc at 2:08 PM on December 27, 2012

There's really no need to double check this. Like you figured out, one is written in "minus cyl," the other in "plus cyl."

Here's your new prescription converted:

+1.00 +4.00 x180
-0.25 +1.75 x178

Looks good to me, and I've been making glasses for over half of my 37 years. :)
posted by tkerugger at 2:39 PM on December 27, 2012 [1 favorite]