That's cause PD is measured by the optician separately when you're ordering your glasses, not by the optometrist or opthalmologist who writes the prescription.

In other words, it's not part of the prescription, it's instead part of the glasses fitting process.

A non-eye related example would be if your doctor prescribed you a brace and the person at the medical supply store measured you to find out which size you need.

...and can be measured at home using a ruler and a mirror, pretty simply. Close one eye, align the ruler at 0 under that pupil. Open the other eye, close the first, read off the distance to the 2nd pupil.

Did this for my wife recently. We measured multiple times very carefully, and got it very wrong.

Did it for myself. Ordered online. Best glasses yet (I think mainly thanks to a my very patient optometrist.)

I measured by taking a picture of my face with a credit card for reference and measuring the pixels with the measuring tool in GIMP. (These were the actual instructions on the website I ordered my glasses from.)

Also worth mentioning I paid $40 ordering them online, in the article it says he paid $280!

May I ask you where you ordered them?

Edit: Just found out they ship worldwide for €3.

https://www.glasses24.com/customer-support/shipping-and-deli...

I was amazed because until a friend told me about this site, I've been paying hundreds of euros just for the frames! At such a low cost, I could even order slight variations on the strength.

They have a lot of options for better lens material, have it darken in sunlight, anti glare coating etc, but I just got the cheapest one and it was fine.

I found that it's easier to do it yourself than have someone else do it -- my wife and I measured mine, hers was off from mine by 6mm (2mm on one side, 4mm on the other, I have no idea how she was nearly half a centimeter off, maybe my eye moved), I ended up going to an optician a few months later, and my measurement was exactly the same as what they measured with some device.

Don't see how you can possibly do it for anyone else, using the mirror method, without getting it very wrong.

Another way is to look through binoculars, get them adjusted just right and then measure them. Don't try to measure center to center. Assuming the eye cups are the same measure from one side to the other (left edge of one to left edge of the other).

I measured my kids using just a ruler and they're all happy with the results. I also measured myself using a mirror, ruler, and a phone camera (so the measurement couldn't be skewed by eye movement) and my results also turned out great. However, I can understand why it would be easy to measure incorrectly, since the ruler is never very close to the eyes.

I have done this a few times, and got inconsistent results. Distance to mirror, or camera to face, positioning of the ruler, they all seem to induce variability. Once I got a reproducible result and went with that, ordered progressive glasses online and they were… off. On another occasion I got PD (and prescription) numbers from optometrist at Visionworks, then took numbers and ordered from Zenni, and they were… off again. Also this PD number again different from the one I had measured myself. But when ordering directly at the store they were perfect. I even wondered whether they actually gave me the wrong PD number, to "teach" me a lesson not to go order elsewhere. Sigh.

Progressive lenses need much more accuracy to be fitted correctly. This means a mono-PD (separate PD for each eye, not just the distance PD halved) and also a height, usually from "datum" measured for each eye too. This measurement would be different depending on the frame and how it sits/adjusted to your face.

This means the frame must be chosen and fitted to you before any of these are measured.

It becomes a 2D measurement.

There is a lot more to it (vertex distance, pantoscopic tilt etc) but the above is the absolute minimum.

Maybe use a mirror, ruler and a camera?

Ed: i see @andai made a similar comment.

Might indeed be better to use a "long" object to indicate pixel length by division (credit card is 5432 px = 5 cm) rather than going by a ruler which might typically only be accurate to 0.5mm at best anyway.

There's no reason for them to not give it, as it's an easy item to address.

In the US, the person who takes your pupil distance (PD) usually isn't the person who writes your prescription. One is a doctor and the other a technician.

When you go to an optician, the doctor takes you in the back and determines your prescription. Then you go out front to the showroom and pick out your frames. There is usually a technician out there who will take the PD measurement and combine it with the prescription, and frame and lens selection to make your order. The technician is also the person who fits you with the new glasses when they arrive.

I recently (in US) asked for it, and was given a hand written sticky, begrudgingly after asking why you need it. But once asked again, no further objection.

Your PD isn’t part of the prescription. But the prescription itself must be provided to you by law in the US.

For anyone near a Warby Parker, they'll happily measure your PD in about 30 seconds. Measurements can vary slightly so you might want to do it a few times and average them.

You can also do it online with Warby Parker as long as you have a credit card (to hold under your face; not to pay with).

do they also need the picture of the backside and home zipcode?

if not, sounds like a startup idea.

Now that is a clever way of doing it!

The PD also varies a bit from reading glasses to distance glasses. If you are ordering single vision glasses, you might want to collect both numbers.

Weird. I’m in Mississippi, of all places, and, without asking, my optometrist always sends me off with a printout containing my prescription and PD.

Inter-pupillary distance is among the few things glasses related that can be measured yourself.

That may take some practice. I did it myself once, and was off by about 4 mm. The resulting glasses were incredibly painful. My eyes would try to look in two slightly different directions, and my brain would put the wrong 3D picture together. Whenever I moved my head my eyes would readjust, which took a noticeable period of time, and I could literally feel my non-dominant eye turning itself to find the focus. I chucked the glasses after a few days.

I'm sure it could be done better, but boy, that was an interesting experience I hope to never repeat.

When I bought online from Zenni optical they sent a plastic ruler that you set on the bridge of your nose with a slot in the middle, and can be used to measure PD. It's similar to this: https://store.eyeque.com/eyeque-pd-ruler.html

Thanks for the tip. That would be way easier than doing it with a plastic school ruler.

It's a little hard to measure it by yourself but with a friend it's easy. Just make sure your looking far off into the distance and not at the persons face who is taking the measurement.

I found that the best way to get a nice, precise measurement was to take two pieces of sticky note and punch a hole in them with a pin. Put them on an existing pair of glasses and line up a distant (unless you're getting reading glasses) sharp corner with the pinhole over one eye. Switch to the other eye and see if the pinhole is lined up—if not, adjust the pinhole positioning and try again. Once the pinholes are aligned, you can measure the distance between them.

Much easier than trying to get someone to measure it accurately with a ruler in front of your face, or trying to draw dots with a washable pen in front of your eyes on old glasses, or any of the other methods I tried. The measurement I took appears to be accurate (the glasses I ordered from Zenni using it are comfortable to wear), and it was easy to get a precise and repeatable measurement to within about half a millimeter.

I encountered this in Canada, with an explanation given to me that there was a lawsuit at some point where an optometrist was sued after a client ordered glasses elsewhere based on the provided IPD and got glasses that caused headaches or something like that.

From Wikipedia[1]:

> In both the UK and most of Canada (excluding British Columbia[5]), the PD measurement is classed as a dispensing tool rather than a part of the actual prescription of the person whose eyes were tested, thus there is no obligation for a PD to be provided on patient request.

[1] https://en.wikipedia.org/wiki/Pupillary_distance

As part of GDPR you can request a copy of any personal data. In the UK this is governed by the ICO, and it’s called Right of Access.

https://ico.org.uk/for-organisations/guide-to-data-protectio...

You get your PD measured at the time you order your glasses. If you never order glasses they'll never measure your PD.

Are you assuming they keep records on the PD measurements of clients who didn't actually purchase glasses there? At least at the opticians I've used, I don't think they do.