I'm not astigmatic. Will the optometrist agree?

June 19, 2014 3:52 PM

My last few glasses prescriptions have come up with 0.25 dioptres of astigmatism in them in various directions (i.e. not consistent between eye tests). I've only had my eyes examined because I've needed to buy new glasses, not because of any difficulty seeing, but I've not enjoyed the effects of getting used to new astigmatism correction on new lenses, and can't help but feel it's spurious precision in the testing.

Would you discourage me from asking for a spherical prescription in my forthcoming eye test? If you think the spherical prescription is fine, how do you suggest asking for this in a UK opticians? I'll be buying the glasses online, so I don't want to ask too many favours of the optometrist. Which chain do people feel is most flexible this way?

posted by ambrosen to Health & Fitness (9 answers total)

I'll be buying the glasses online, so I don't want to ask too many favours of the optometrist.

You don't have to provide the astigmatism part of the prescription to the dispensing optician. Just order the glasses with the "cyl" part set at 0.

On the other hand, I'm a little puzzled by what you mean by "spurious precision." The optometrist presumably is giving you the A/B "is it better like this, or better like this" test. I know that sometimes you just can't tell if A really is better than B or not, but it would seem odd that the optometrist would insist on a correction if you weren't reasonably consistently preferring the option with the correction than without. I'm also a little puzzled how you even know that what you're having difficulty "getting used to" is specifically the astigmatism part of the correction. .25 dioptres is pretty minimal (I have more than that in both eyes). I don't know how you'd be sure that it wasn't over or undercorrection of the myopia or presbyopia that was causing the problem--or even just some other problem like poorly fitting frames that have your eyes in the wrong part of the lens.

All of which is just to say that I think a longish talk with your optometrist and some rigorous testing of all the various parameters involved is probably the smarter move than simply leaving the "cyl" part of the prescription blank when you order some new specs.
posted by yoink at 6:15 PM on June 19, 2014 [4 favorites]

Would you consider going to an ophthalmologist, which might give you a more reliable reading you can trust?
posted by Kololo at 8:30 PM on June 19, 2014

One thing that might be getting you a different prescription than what's really best for your eyes is bad instructions on what it means for "A" or "B" to be better — I've found it's often more helpful to describe how it's better. So, for instance "A seems better and it's brighter" or "B seems better but it's smaller". I've had some eye doctors who tease out those kinds of answers, and some who don't, but even those who don't seem to appreciate the information.

I also don't think it would be at all unreasonable to tell the doctor up-front that you've gotten prescriptions in the past with astigmatism correction, but that the values have been very inconsistent and you've been happiest with your vision without it. You're not trying to tell the doctor whether you do or don't have astigmatism, just what's worked well for you in the past. That doesn't seem like asking favors, to me.
posted by duien at 9:12 PM on June 19, 2014 [1 favorite]

Yeah, I'd just talk to the optometrist. I have mild astigmatism, but worse than yours. .5 I think. I wear both contacts and glasses and the glasses have the correction but the contacts don't. According to the optometrist, they usually put the correction in the glasses, because it's easy/cheap, but most people don't miss at such low levels and so they don't do it for the contacts, since toric contacts are more expensive. So it might not be a problem at all.

I wouldn't leave the astigmatism off your online order. At least in the US, they're required to check against a scan of the Rx and make sure they're the same.
posted by matildatakesovertheworld at 9:41 PM on June 19, 2014 [1 favorite]

At least in the US, they're required to check against a scan of the Rx

I've ordered glasses online from three different places and have never been asked to provide a scan of the prescription.
posted by TWinbrook8 at 5:59 AM on June 20, 2014 [1 favorite]

Nthing just talk to your optometrist.

I have a mild astigmatism as well, have been given a glasses prescription which includes astigmatism correction, and then returned them after a few days because I honestly could not get used to it. I got new lenses free of charge, although I went to the optician in my optometrist's office.

I talked to my doctor about it, and now he writes me a script without the astigmatism correction, and I can take it wherever I want to order glasses.

I've never ordered glasses online, so I don't know if they have similar return policies, but one advantage for me of getting my glasses through the optician that works with my optometrist is that they will replace the lenses (free!) if I don't like them--even if the script was filled exactly as prescribed.
posted by inertia at 7:14 AM on June 20, 2014

(Using fractions for diopter msmts for clarity below.)

yoink: On the other hand, I'm a little puzzled by what you mean by "spurious precision." The optometrist presumably is giving you the A/B "is it better like this, or better like this" test. I know that sometimes you just can't tell if A really is better than B or not,

Oddly, you answered your own puzzlement.

AFAIK, 1/4 diopters is the nominal "resolution" of eye correction. +/- 0.5 resolution units is the size the quantization error. Therefore, saying an eye is 1/4 diopter astigmatic is essentially saying, "There's a barely noticeable astigmatism in your eye's performance."

Similarly, the direction of astigmatism has a resolution to it, as well, that is not as well defined (they may say something like "2 diopters at +17 degrees", but that doesn't mean anyone could possibly distinguish this from 2 diopters at +18, or even +20, degrees).

However, if you get a reading of "1/4 diopter at +X", and someone else reads "1/4 diopter at X-90 degrees" or "X+90 degrees", one of them (at least) is dead wrong.

Myself, I wouldn't worry about it at all. 1/4 diopter is damned near 0. Skip the expense of toric lenses (lenses cut to accommodate astigmatism), and just go with the regular part of the diagnosis.

Caveat: I am an optical engineer, but have no qualifications as an optometrist.
posted by IAmBroom at 1:50 PM on June 20, 2014

I have a minimal astigmatism in one eye that is corrected with glasses. When I wear contacts I don't bother with the astigmatism correction, and I can function just fine, but something is off about my vision.
Like you say, it's hard to put your finger on how your vision is better/worse with/without the correction. In the end I wind up wearing my glasses most of the time because of the superior correction. I think that leaving the astigmatism uncorrected affects my depth perception in a subtle way.

Maybe talk to your optometrist about sampling contacts that don't correct your astigmatism.
posted by Deodand at 10:57 PM on June 21, 2014

Response by poster: Thanks all for the effort you put into answering this. It's been something on my mind for a while, worrying about slightly misfitting glasses leading to general worsening of the prescription (and written out like that, it sounds rather silly).

I got the eye test done today, and mentioned my concerns, and the optometrist took care to make sure I had time to look at the astigmatism dot patterns and offered to let me do extra comparisons, and was generally very helpful. In the end I came away with a prescription slightly weaker than on my current glasses, and yes, with no cylindrical correction at all.

For what it's worth, for readers in the UK, I went to Vision Express, and got a lot more interaction with the optometrist there than when I've been to (multiple different branches of) Boots previously.
posted by ambrosen at 3:48 PM on June 22, 2014 [2 favorites]