When I am filling in my prescription at the online prescription glasses store PrescriptionGlassesOnline.net, there is a cue “Enter PD”, could you please advise what is PD? Thanks for your help.

PD is short for Pupillary Distance, is the distance between the centers of your pupils in millimeters (mm). If there is no PD value listed in your prescription, you may ask your optometrist the PD value.