Is this a possible typo on my glasses prescription?

August 2, 2015 7:15 PM

Help interpreting glasses prescription.

I am mildly nearsighted and when I went to the ophthalmologist last year the prescription in my left eye was just a little worse and the doctor told me I had developed a touch of astigmatism in one of my eyes (can't remember which). I was about to order glasses online from Zenni Optical and wondered if something might possibly be off in the "axis" part. My prescription says:

OD: -1.50 sphere, -0.25 cyl, 160 axis
OS: -1.75 sphere, -0.25 cyl, 016 axis

I wondered if the axis could be a typo because it would seem to indicate something is wildly different between my right and left eye, whereas my contact prescription is just mildly different to the point that it's not really noticeable if I mix them up when I put them in. Also because the digits are the same so it would make sense as an error.

I guess the short version is what is axis and is it normal for the two axis numbers to be almost opposite in people with mild vision correction?

posted by mermily to Health & Fitness (10 answers total)

Axis describes where (in degrees) the astigmatism is. More here. It's no likelier that it's a typo than if the numbers were similar.
posted by chesty_a_arthur at 7:27 PM on August 2, 2015

The axis tells them where to locate the cylinder. It is measured in degrees form 0 to 180. So, the axis number is not about the strength of the correction but how to place it to properly correct your astigmatism. There is more here.
posted by metahawk at 7:28 PM on August 2, 2015 [1 favorite]

Here's How To Read Your Eyeglasses Prescription.
posted by MsMolly at 7:28 PM on August 2, 2015 [2 favorites]

I've had a similar difference between the two axes in my prescriptions for decades. Many people have even more substantial differences in the prescriptions for their two eyes, and astigmatism develops independently in each eye. There's always a chance for error, but it's quite likely correct.
posted by eschatfische at 7:30 PM on August 2, 2015

Best answer: This is totally normal.

The correction for astigmatism (the cyl and axis numbers) is symmetrical and runs from 0 to 180, with 0 and 180 being the same. So 160 is not that different from 16 at all, only 36deg difference. That said, there is no reason to believe that your eyes couldn't have astigmatism on different axes.

Bear in mind that -0.25 is a very weak correction and 16-20 deg is not much off the axis of your primary correction.
posted by ssg at 7:32 PM on August 2, 2015

Also, your contact prescription probably doesn't cover astigmatism at all, so has no bearing on this.
posted by ssg at 7:35 PM on August 2, 2015

I had a bad prescription once due to a transcription error by the optical assistant; she copied the prescription to the prescription pad from the doctor's exam sheet. As a result, my bifocal prescription was off and weird. Unless they've gone electronic (been a while since I got an eyeglasses prescription-- LASIK FTW), any transcription like this is an opportunity for error, but this is something that can be checked over the phone. Call the eye doctor and confirm the numbers; it's a piece of cake that should take 5 minutes at most if they have to pull your file. Unless you're talking to the doctor directly, you likely won't get any medical info re: your astigmatism if you have questions about it, but you can at least get your prescription underway. Just do them a favor and wait 30 minutes after they open before calling.
posted by Sunburnt at 7:48 PM on August 2, 2015

Mine has a substantial difference betweens axes as well:

OD: -6.25 sphere, -1.50 cyl, 020 axis
OS: -5.75 sphere, -1.00 cyl, 115 axis

I'd be more suspicious if the two were identical.
posted by HillbillyInBC at 8:38 PM on August 2, 2015

Best answer:
The correction for astigmatism (the cyl and axis numbers) is symmetrical and runs from 0 to 180, with 0 and 180 being the same. So 160 is not that different from 16 at all, only 36deg difference. That said, there is no reason to believe that your eyes couldn't have astigmatism on different axes.


They're actually even more similar than this.

It's common for people to have symmetrical astigmatism, rather than identical astigmatism. But the axis in your prescription is anticlockwise for both eyes. The mirror image of 16 degrees is 164 degrees, so your eyes are nearly identical.

Apparently my eyes have the unusual condition of having astigmatism is the same direction for both eyes, not mirrored. I don't know how rare it is, but I did ask my optometrist about it once and he said that usually they're mirrored.
posted by aubilenon at 11:11 PM on August 2, 2015 [2 favorites]

Just a note for using Zenni (I thought about this instantly when I just read the question topic). They don't believe my prescription is real. I mean when I enter it I get an error saying "Please enter a valid prescription." So for a while there I thought mine had a typo or something but every other online glasses retailer will take it and subsequent prescriptions are all about the same.

Your prescription is pretty standard but in case you run into something similar.
posted by magnetsphere at 6:28 AM on August 3, 2015