Measure Pupil Distance
Pupillary distance (PD for short) is used for proper fitting of prescription glasses. As an adult, your PD never changes - even when your prescription changes. You can request your PD measurement from your optician when you receive your prescription. You can also easily measure your PD yourself:
Place a ruler with millimeter measurements on your nose, with the starting point centered on the pupil of one eye
Stand in front of a mirror and look straight. Measure the distance from the centre of the first pupil to the centre of the second pupil. A friend can help in reading the measurement but they must be at the same height as you.
The PD value should be accurate so that your prescription glasses are sized correctly for your face; we recommend that you confirm your PD properly by taking the average of 3 measurements.