THE PUPILLARY DISTANCE (PD)
PD or Pupillary Distance is the distance between the pupils of both eyes, center to center in millimeters (1 inch = 25.4mm). Many optometrists omit this to supply this value, crucial for a perfect centering of the optical corrections. But it can be measured at home (see below.)
Most people have a PD measurement that falls within the 54mm to 74mm range. PD may be written as 32/34.which are the right eye and the left eye partial PDs from the center of the nose to either eye. In this case the total PD is the sum of the two, 32+34. = 66.
Contrarily to what opticians might tell you, measuring our own P D at home is quite easy :
if you've never worn prescriptions glasses to date
You cannot order your glasses online. You should absolutely go to your eye doctor for an accurate and complete prescription that will also include your PD. You'll have it valid at hand for 2 years.
If you already wear spectacles,
You just need: your existing eyeglasses (don't care much about the prescription providing you can see through the lens), • a non-permanent marker, • a third person help .
How to do it: Stand in front of the third person and look at the distance, not at the person. Ask him/her to mark on your lenses the points that correspond to your pupils with the marker. Then measure your total pupillary distance as well as the partial right and left PDs running from the center of your nose to the respective pupils. Redo the operation 3 times to ascertain that you have the correct measures.
Remark: this simple and easy type of measurement has been used for dozens of years by optometrists worldwide till very recent years. And it still works fine.