How accurate must PD be? Eyeglasses
m...@privacy.net
times at Costco so can order glasses online
Each time it has been one half to one complete mm off.
How important is PD and how accurate must it be?
I'm thinking I should take all three measurement and
average them and use that.... one for the right side
and another of the left side. Good idea?
Rod Speed
> I've had my PD (distance between pupils) measured
> three times at Costco so can order glasses online
> Each time it has been one half to one complete mm off.
Thats nothing much.
> How important is PD and how accurate must it be?
Not very, the use of over the counter glasses proves that its not that critical.
Its just the distance between the eyes, and clearly
with simple prescriptions, the distance isnt that critical.
> I'm thinking I should take all three measurement and
> average them and use that.... one for the right side
> and another of the left side. Good idea?
Cant do any harm to use that approach.
bart.c
<m...@privacy.net> wrote in message
news:6qgp46dtsi6t4jldq...@4ax.com...
Mine has been measured at 62 to 65mm at various times.
I don't think it's critical, as this distance varies anyway (when you look
at closer objects, the pupils come together), and your eyes will make minor
adjustments themselves, within reason.
(But if you want to double-check it yourself, use a ruler and a mirror: look
at the right-hand eye in the mirror, hold the ruler so the 0-mark is aligned
at the centre of the pupil; now look at the other eye in the mirror, and
read off the distance on the ruler of the centre of that pupil. Now you have
your PD for when both eyes are looking straight ahead.
Another way is using an existing pair of specs: draw a vertical line on a
sheet of paper. Hold one lens over the line so that the image through the
lens is centred (line is not refracted left or right). Mark lens with centre
of line with a dot. Repeat for other lens, and measure the distance between
dots. But note that with reading (close-up) specs, the lens centres may be
nearer than your PD for distance)
--
Bartc
John Weiss
Depends on the glasses...
With bifocals or trifocals with narrow field of view in the inset
lenses, it will determine how well you can see at close ranges. With
progressive lenses, many of which have an EXTREMELY narrow field of
view in the mid- and/or close-range fields, it can be critical to eye
comfort.
My wife was never able to adjust to the progressive lenses she got from
Costco, even though she got the measurements in the store, not online.
With proper measurements and good lenses from another optician, she
adjusted rapidly.
Salmon Egg
"Rod Speed" <rod.sp...@gmail.com> wrote:
I measured that distance by holding a metric tape (not strictly
necessary) under my eyes and having my picture taken. It was no problem
reading the scale to about a millimeter. Even if there is an error, it
is equivalent to having a bit of prism added. It is a relatively simple
thing to calculate, but it dependent upon the spherical correction. I
chose to have my error on the side of additional convergence because one
ey points out.
Bill
--
An old man would be better off never having been born.
Jeff Thies
If you are adjusting to your glasses don't worry. Note that near PD
will be different than far, just to give you one more thing to be
troubled by!
Less worry, more be happy!
Jeff