Do I have the wrong pupil distance

[Barb]

Maybe you guys can help me out on this. I just ordered eyeglasses
from Zenni. I ordered a pair for me and a pair for my boyfriend.
When I put mine on they seemed a little off. I can see everything
clearly but it just doesn't seem right. My boyfriend originally
measured the PD at 57 and I just had him take a picture with me
holding a ruler and it looks like it's 55. Would 2 mm mess it up that
much. I also closed each eye and can see well using only one. It's
when I use both eyes together that it seems a little wierd. I also
wear contacts and noticed that the axis on my contacts and glasses are
different (Right eye contacts: x150, glasses x137). Could that be
why? I'm not too upset since I only spent $30. Do you think I should
order at the smaller PD? Thanks for any info you might have.

[higherorderaberration]

Yes, a 2 mm difference in pupillary distance can cause a pair of
eyeglasses to feel off because your pupils tend to converge or diverge
to the center of the lens. (I made a similar mistake as yours but in
the opposite direction.) Remember that your eyes only converge about 3
mm or so from distance to reading focus; pupillary distance is more
crucial the higher the power of your prescription.

The other thing that could be wrong is caused by the lax tolerances in
the optical industry (which are more of problem for lower power
prescriptions). I've had good experiences with Zenni, however. For
lower prescriptions the ANSI tolerances are 1/8 D. (Many manufacturers
are certainly more accurate than this, however.) Lens powers only come
in 1/4 increments. Because errors compound, if your actual perfect
correction is say, 5/8, you could end up with glasses in which one
lens is off by 1/4! (This happened to me--the replacement lenses I
ordered were BOTH off by almost 3/8 in divergent directions! With my
sphere of -1.25 and -0.5 (plus -0.25 of astigmatism), I was quite
annoyed, as my left eye went from fully-corrected 20/9 vision to a bad
20/20 (meaning that I can barely make out those letters) and the
binocular balance was so off that my eyes had trouble using both
images. (My uncorrected vision is about OD 20/50 or more and OS 20/30
but my brain had adapted over time to that. Uncorrected, with both
eyes together, I see a bad 20/25.) This company, which is not one that
has been mentioned by this group, also sold me a chipped lens and
attempted to cover it up by hiding it under the frame (the glasses are
half-rimless) and also "lost" a screw on a nose pad. These frames were
almost new. Jerks.)

You can test whether your sphere is accurate with the duochrome test.
(I made my own in windows Paint and can post it.)
If your cylinder (astigmatism) is high, a different axis may need some
adaptation time. You can test the accuracy of your prescription and
the extent of your astigmatism with a starburst chart (http://
www.sinepatterns.com/images/Sector%20Star.gif), which is used to test
cameras, or you can use a clock dial.) I can help you with these or
you can go to your doctor to make sure your prescription is still
accurate. They sometimes do change! You may wish to make sure your
lenses are accurate before you reorder. Do optical shops still do this
check for free? Anyone?

By the way: an interesting simulation I found is http://www.billauer.co.il/simulator.html.
So, yes, you absolutely can tell the difference between small changes
in lens powers, despite what the optical jackals say. (Really people,
the human eye/visual system is amazingly powerful.) In general, visual
differences are more readily detectable (thank you, Edward R. Tufte)
when they are presented spatially rather than temporally (as your
doctor does because he must).

Furthermore, because the eye has a significant amount of chromatic
aberration, small changes in power move the wavelength of light which
is sharply focused on the retina and they are important in preventing
over- and undercorrection. (My own eyes bear this out as I detailed
above.) Also, usually the lens in your eye will adjust the power at
closer distances--so that you still see the same--but far distance
vision may be off. Poor long-distance vision may or may not annoy you.
(Notice that you're usually tested at 20 feet which requires a not
insignificant amount of accommodation! Are they all quacks? Sigh...)

As you can tell, I've been learning way too much about this field.
But, I don't sleep.

Matt

[mzdtk]

yes it could make a bit of difference if you are really senative to
it. Grab a round magnifying glass and try to read only along the outer
edge

[IMQ]

I actually took the measurement myself the day before I went in to see
the doctor for the final fitting on my contact lens. After all it is
not rocket science.

Improvising the tip found on the internet, I took a frame my brother
gave me, stood in front of the mirror close enough to see the centers
of my eyes, then mark centers with the marker right on the lenses. I
measured it to be roughly 70, so I thought maybe I was off because I
didn't think my PD was that wide.

But the next day, I have my PD measured by someone in the doctor's
office. She had me look into this portable thingy and bam, I got my
PD. Just like that. Less than a minute. And they were measured OD:36
and OS:34. So when I ordered on line, I gave the combined PD=70.

On Mar 18, 8:36 am, higherorderaberration <mxs...@yahoo.com> wrote:

[Fred Di]

LOL... what a load of crapola.

A 0.25 difference is barely noticible, even using that ginned up
middle eastern web site you refered us to.

> the extent of your astigmatism with a starburst chart (http://www.sinepatterns.com/images/Sector%20Star.gif), which is used to test

> cameras, or you can use a clock dial.) I can help you with these or
> you can go to your doctor to make sure your prescription is still
> accurate. They sometimes do change! You may wish to make sure your
> lenses are accurate before you reorder. Do optical shops still do this
> check for free? Anyone?
>

> By the way: an interesting simulation I found ishttp://www.billauer.co.il/simulator.html.