
Measuring Your Own Pupillary Distance - walterbell
http://www.daniellivingston.com/2012/06/measuring-your-own-pupillary-distance.html
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Spare_account
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?

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

~~~
Spare_account
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)

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

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

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CalChris
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...](http://www.eyeglasslensdirect.com/Trivex-Single-Vision-
Lenses-s/147.htm)

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/lenses/progressive-lenses/seiko-individual-
lenses/)

[http://seikoeyewear.com/news/seiko-
pcwide](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.

~~~
copperx
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.

~~~
CalChris
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](http://www.mastereyeassociates.com/eyeglass-lens-materials)

~~~
mrob
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.

~~~
CalChris
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/...](http://eclecticeyewearaustin.com/wp-
content/uploads/2016/05/Lens-thickness.jpg)

~~~
boptom
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.

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codingdave
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.

~~~
hatsunearu
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.

~~~
codingdave
> 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.

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

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karlshea
> 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.

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ademarre
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](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.

~~~
wenc
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.

~~~
KGIII
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.

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dave7
> 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!

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mindslight
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.

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watertom
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."

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tbabb
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.

?

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

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

