Pupillary Distance (PD)
The P.D. is necessary. It is the distance between your eyes (pupils) and it allows us to center the lenses properly in front of each of your eyes. While not always written on your prescription, the last place that you purchased prescription eyewear from should have it on file. (It generally does not change much after your early 20s). You should be able to call-in to get it. Technically, it is not part of the Rx, so many doctors do not include it on the prescription. Additionally, most opticians should be able to take the measurement in about 30 seconds or less. (An optician, optometrist, ophthalmologist, etc. should take this measurement, not you or your friend, spouse, etc.)
The PD may either be recorded as one number (total - generally between 50mm and 75mm) or two numbers (one for each eye - generally between 25mm and 37mm).
If you want to continue your order and supply the PD later, simply enter "to come" for now. Call-in or email the information later.