I just got back from an eye exam at Walmart Vision Center. I order my glasses online, so they always write down my pupillary distance on the prescription. I noticed that this time it was 66, when I was sure it had been 68 at my last exam two years ago. They looked it up on my chart and said no, it was 65-point-something last time, rounded to 66.
When I got home, I dug out the old prescription and sure enough, they had written down 68.
How big a deal is this? Should I let them know I’ve been wearing slightly wrong glasses for two years? Should I ask for a refund or discount on my exam? How pissed should I be?
IANAOptician, but I think that measurement only affects the frames and how comfortable they would be. And since there’s a range to that measurement that a given set of frames would accommodate, it probably didn’t make a difference.
Um … no, voltaire. Nothing changes about the frames based on the PD measurement. That measurement is used to set the distance between the optical centers of the lenses.
Lenses are ground using spherical approximations to the theoretically ideal curves. The optical center is the point at which, when you look through the lens at that point, the curve is exactly equal to that theoretical ideal; the farther away you are from the OC, the more ‘spherical aberration’ you get in the lens.
When a lens is cut to fit a frame, it’s cut in such a way that when the wearer looks straight ahead, they’re looking through those optical centers and getting the ‘perfect’ amount of correction based on their prescription. The PD measurement is used to calculate how to do that. So if they wrote down 68 when your actual PD is 66, those OCs were each set 1 mm too far to the outside. When you looked straight ahead, both eyes got the correction you’d ordinarily expect when looking 1 mm to the left or right (measured at the distance from the eye to the lens); when you looked 1 mm to the left, your left eye was getting perfect correction but your right eye was getting what you’d normally expect at 2mm offset, etc.
How serious a problem this is depends a lot on your prescription. If you have very serious astigmatism, this would be very noticeable; for a small prescription, not so much. (One of the reasons that very strong lenses are preferably made smaller is that the spherical aberration increases much more rapidly for those prescriptions.)
[qualifications: I used to make quality custom eyeglasses in about an hour]
They looked it up in my chart and told me it was 66 last time.
This is interesting because I’ve just recently noticed (by accident) that while my distance vision has declined noticeably, I can turn my head a little and see quite a bit better out of the sides of my glasses.
My prescription is fairly strong; -3.75 and -5.50 with astigmatism in one eye.
I think this represents a deviation of 2 millimeters. So, not very mad at all. There will always be a variance in taking empirical measurements. This error sounds well within acceptable tolerance levels (i.e., a couple millimeters is not going to effect the fit or field of your eyeglasses).
This is called in science “the power of suggestibility” … You back-remembered this symptom upon reading SCSimmons’s post. Your glasses are fine; don’t let this become a somatic preoccupation.
No, I noticed a week or two back. I was having trouble reading the closed captioning on TV and inadvertently looked at it sort of sideways. The words are distinctly blurry through the center of my glasses but much clearer through the edges. I assumed that my vision had declined and that the script was stronger at the edges; my lenses are thicker at the edge.
I just found out about the PD discrepancy today. Also, it isn’t that they measured differently last time; they had the correct measurement in my file but wrote it down wrong on my paper script, which I then used to order my glasses.
Mistakes happen. Especially transcription errors.
If it was a serious issue, you’d have really noticed…
My prescription is in the -8 range with astigmatism; a few years back my opticians measured both of my pupil centres about 2mm too high or too low relative to the new frames. The day after getting the new lenses I got pretty violent motion sickness that persisted for a while even after changing back to my old glasses [experiments where people have worn inverting lenses for a period have shown the brain is pretty darn clever at compensating eventually, but will make you suffer while it adjusts]. All I ended up paying for was an additional eye exam for them to figure out what had happened. SCSimmons has already covered the explanation.
As a consumer advocate, I’d be very pissed if, upon being notified within a reasonable amount of time that your vision wasn’t crisp, Walmart Optical didn’t either refund your money or give you a free replacement set of glasses. I’d say that “reasonable time” expired about 1 year and 11 months ago, which is 30 days after they performed a vision test with the new glasses on your face, and you gave the thumbs up.
Now, now, Walmart Vision Center (actually Ford Family Eyecare, unaffiliated with Walmart) is a perfectly cromulent option for an eye exam. Certainly the same as one of those mall eyeglasses stores. Does anyone really go to an ophthalmologist for their pre-glasses exam?
Now, see, this seems like a good reason to be pissed. You had to pay for them to figure out how they screwed up?
:smack: Aargh! The hidden downside of buying cheap glasses online!
Then extend the “reasonable time” to 30 days after you put them on your own face. Seriously, if you didn’t complain in 2 years, then I can’t say that I’d expect a business to do anything. They can’t make right what they haven’t been told is wrong.
Well, technically I only paid for one of the eye tests as I’m entitled to one per year on expenses Compared to the price of the lenses themselves it’s almost (but not quite) trivial. Had the first test not been free for me, I’d have kicked up a stink. Mostly I was glad not to be feeling nauseous.