Measuring Your Own Pupillary Distance | Hacker News Reader

Measuring Your Own Pupillary Distance

daniellivingston.com

65 pointswalterbell36 comments

From the article:

I tried it out. Eight times. With eight different photographs. It measured me from a 61mm to 65mm PD. So call it accurate within ±4mm. How bad can that be?

I'm no mathematician but shouldn't that be ±2mm? And if so, then the following paragraph (where he says that glasses should be within 2mm to be usable) confirms that this method would suffice?

Also from the article, his actual PD is 69mm...

OK, I'll admit I didn't get that far.

But that means the method was accurate ±8mm?

Still not ±4mm...

(Unless I don't understand the ± notation)

1 face probably isn't enough to characterize the accuracy of the method.

Well that kind of invalidates the entire article then! ;-)

I tried doing it myself as well and came up higher than what my reality was by a couple mm as you describe. I ended up calling up my optometrist and provided my correct number no problem.

It's a mistake :-)

http://www.daniellivingston.com/2012/06/measuring-your-own-p...

AnonymousSeptember 12, 2013 at 1:02 PM It measured me from a 61mm to 65mm PD. So call it accurate within ±4mm.

Uh, no... This is ±2mm (around a center value of 63)

Daniel LivingstonSeptember 12, 2013 at 6:10 PM Oh yes that's true, I meant to explain it is inaccurate by up to 4mm.

Depends on your Rx, but 4mm can be quite the headache at the end of the day each day.

I don't think PD is part of your optometrist's prescription; it wasn't on the prescription they gave me when I walked out the door. I can't remember who measured it but I copied it down from my optician's order when I ordered some glasses. They're both in the same office (which is pretty common) at Berkeley School of Optometry.

My PD is L 32.5 R 31.5. The ruler technique is neither this accurate nor does it distinguish left from right. Yeah, I'm a little lopsided.

I keep this information now in a Google Doc along with my eye size, bridge size, temple length and current frames. Since I'm a nerd, I read up on lens materials and now I use Trivex single vision aspherics for readers and drivers. I'm a lot more knowledgable now about my available choices. These are some of the Trivex single vision choices:

http://www.eyeglasslensdirect.com/Trivex-Single-Vision-Lense...

If you have major astigmatism problems you really must educate yourself on the choices. There are free form lenses with much more complicated computer driven prescriptions+lenses customized to the individual. Also, you can get free form lenses tailored to computer use.

http://seikoeyewear.com/lenses/progressive-lenses/seiko-indi...

http://seikoeyewear.com/news/seiko-pcwide

Another thing is that if you ask your optometrist for a prescription for readers, they'll usually set the focal distance to something like a foot. Well, I'm typing on my laptop and it's about 3 feet away. This is intermediate or tool distance and a prescription for that is a massive quality of life improvement.

If you spend some time on an online site like www.framesdirect.com, you can educate yourself quite a bit on the available choices. When you walk into an optician's office, they really only have a certain amount of time to work with you since they have to make a nickel; so you usually spend a lot of time on frames. I haven't even ordered online yet but educating yourself before you walk into a brick and mortar optician's office will make you a little annoying but then you'll get a better result.

> I don't think PD is part of your optometrist's prescription; it wasn't on the prescription they gave me when I walked out the door. I can't remember who measured it but I copied it down from my optician's order when I ordered some glasses.

It wasn't on mine either, but on advice given to me I called up the optometrist to ask and they gave it to me with no problem at all.

I've started keeping//tracking my prescription some time ago just for good measure.

My optometrist refused to give it to me unless I bought glasses from them. They claimed the number depends on the specific glasses you have.

Fortunately I was able to find it on a prescription from a previous provider.

I'm glad you were able to get the information from a more reasonable provider.

I guess I was lucky to some extent, and I hope we're all able to find "better" providers.

Your pupillary distance won't change depending on the frames you buy (it is a body measurement after all).

However, where the optical centre of a lens is placed within a frame can vary from the PD a fair bit, depending on how the frames sit on your face, as the contact point of the frames do not always line up perfectly with the top of the nose bridge.

Also, an oft looked over measurement is the distance from the bottom of the frame to the centre of the lens, which is important with complex prescriptions and cannot be measured without looking at the frame on your face.

Having said this, with most low prescriptions the human tolerance is so high that it does not matter.

Isn't Trivex optically worse and more expensive than the standard CR-39 and just insignificantly less thick? I have a -4.00 prescription, and I didn't think Trivex was worth it, because I don't need shatter protection.

Also, interestingly, in Mexico PD is part of the prescription.

Not optically worse.

CR39 has lower index of refraction (1.498 vs 1.54) and so it is heavier. It has worse chromatic aberration (Abbe 58 vs Trivex 45). So it's really only good for light prescriptions.

Trivex is also easily drillable making rimless easy, rimless->lighter; PC tends to crack easily.

But yes Trivex is a little more expensive than CR39 but in my experience a lot better. If your lenses last 2 years, lenses are not where you should save money.

http://www.mastereyeassociates.com/eyeglass-lens-materials

CR39 has better chromatic aberration. Higher Abbe number means less aberration. CR39 has the lowest chromatic aberration of any material commonly used to make glasses.

Yeah, I got that backwards. Point is that CR39 is not exactly better optically. Trivex is significantly better chromatically than PC, 1.60, ... In addition, Trivex acts as a UV cutoff filter.

What I couldn't figure out is whether a CR39 lens' comparative thickness (prism length) vs a thinner Trivex lens degrades its chromatic aberration advantage in practice.

http://eclecticeyewearaustin.com/wp-content/uploads/2016/05/...

Generally, you would expect lenses with a higher refractive index to be thinner.

However, due to the selling point of Trivex being "shatter proof" it has a greater centre thickness (to pass safety lens regulations), and thus the edge thickness is also comparable to CR-39.

> Well, I'm typing on my laptop and it's about 3 feet away.

My eye doctor (don't remember which one he is, sorry) recommended bifocals that are computer-range above, reading below.

Simply fantastic. Couldn't recommend it more.

Well, I'm nearsighted. So I can type on my phone without glasses at all. So I was really kinda annoyed when they set the focal distance on some progressives I had to 1 foot. Laptop reading was possible but uncomfortable.

I have given up on progressives altogether. Single vision for me is awesome. But my big recommendation is to educate yourself on the choices available cuz you can't expect an optometrist/optician to do this in five minutes.

Whichever way you go, you're absolutely right to get what is correct for you, which (usually) requires digging on your own.

Luckily for me, as I say, my eye doc recommended that layout.

If there really are "30 other ways" the online vendors can ruin my glasses, I'd much rather read a detailed post about those specific reasons than hear more vague complaints about their industry getting disrupted by online sales.

While I used to use Zenni glasses online and had some success with them, I really should have known better and shouldn't have taken a risk like that (though obviously it's not gonna do super permanent damage if any since I didn't wear it too long).

I wouldn't be surprised if their lenses were not the correct power, and if their cylindrical prescription is on the wrong axes, etc. I don't trust some random sweat shop in China doing this (don't quote me on this but I am pretty sure the operations is done in China).

Since the frame market is monopolized by some sleazy business, I wish I could just buy a decent frame from Zenni and give it to a qualified local optician who can fit a nice lens in it.

> I wish I could just buy a decent frame from Zenni and give it to a qualified local optician who can fit a nice lens in it.

Why can't you? I know opticians who will put modern lenses into antique frames, so I have to imagine they can do it for modern frames even more readily.

Oops. I just didn't know that was a possibility.

> want to buy glasses online, without the expense of an optician's expertise. Ok, fine. I'm a professional optician and I have reasons to hate that people do this.

Well maybe you should offer some frames priced under $400 and people would buy them from you instead.

I once tried to measure my own pupillary distance using the ruler-mirror method.

I failed and the glasses I ordered were unusable. In the end I brought them in to my optician's office where they precisely measured not only my PD but a couple of other metrics that I think described the frame/lens position on my face.

I sent all those measurements to the vendor (https://www.warbyparker.com) and the second glasses were perfect.

These other self-measure methods look better than the ruler-mirror method that I did, but if I ever buy glasses online again, I'm going to take the trial frames straight to the optician's for proper measurements.

I tried the method in the article and got a pair of sunglasses online from FramesDirect that were incorrectly made. I'm not convinced that it works.

My optician has a tool that measures my PD correctly every time. Unfortunately they are reluctant to give me the PD measurements for fear of losing my business.

So we meet half-way. I find frames online and I get the optician to put lenses in them.

It's your prescription. It's your health data. Don't take no for an answer. I'm almost positive that they are legally required to give you that data. Asserting your rights is not a bad thing.

To add to this, I get my prescription from the doctor, but I still buy glasses from them. They will open up on a Saturday for me. I've ordered what I consider to be disposable glasses online.

The $10 method to measure PD:

https://www.harborfreight.com/6-inch-composite-digital-calip...

> There is only one reason you would your want your own PD measurement: your want to buy glasses online, without the expense of an optician's expertise. Ok, fine.

Fair enough, the article is from 2012.

Today, there is another legitimate use for knowing your IPD - VR headsets!

An incorrect IPD setting as explained in this article can over time teach double-vision and other problematic things you do not want. In VR, given the things aren't used for such large durations as normal eyeglasses the more likely effects are discomfort / headaches and (unique to VR) an improper appearance of world-scale. It's still worth getting it right!

Is PD actually defined as the distance between your "vision-rays" at the surface of your eyeballs, or at the plane of the (manufactured) lenses?

I've been meaning to order glasses online (eg Zenni) forever, but haven't gotten around to it. My theory is that ordering online will allow me to go with several pairs of much cheaper CR-39 and then not care as much if they get scratched, rather than ending up with an expensive proprietary plastic and then wanting to pile on the upsell of scratch resistance, etc. The chromatic aberration of polycarb is horrendous.

Why not just have your optometrist provide pupiliary distance as part of the prescription as they are required by law?

Prescription absolutely requires the PD. I told my doctor I needed to order special safety impact glasses through my employer. I need to buy them through my employer for their insurance purposes, and my doctor's response: "Oh, I'll need to add the PD otherwise they can't make the glasses correctly."

What about this:

Look squarely in the bathroom mirror. Hold your head firmly against something to prevent movement.

Close your right eye. Use a fine tipped dry erase maker to make a dot over your left eye's pupil. Then close your left eye and make a dot over your right pupil. Measure the distance between the dots.

I just have my wife do it :-) (she's former optician, and calls the ruler she uses a "PD stick")

Since it's not part of a prescription, my opthalmologist just gave it to me over the phone.

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