Why PD Is Important
PD means “pupillary distance,” which is the distance between the center of each pupil. This measurement is used to determine where you look through the lens of your glasses. If the PD is wrong, or as we say in the optical world “out of tolerance,” you won’t be able to focus your eyes together properly. That’s why it is important to make sure that your PD is as accurate as possible.
Single PD Vs. Dual PD
A single PD is one number that represents the measurement of the center of one pupil to the center of the other in millimeters. The average adult PD range is between 54-74 mm. The average child PD range is between 43-58 mm.
A dual PD is provided with two numbers and represents the measurement of each pupil center to the center of the bridge of your nose in millimeters. An example of a dual PD measurement is 32/30. The first number corresponds to the right eye and second number to the left eye.