What is Pupillary Distance (or PD)?

Your pupillary distance, or PD, is the distance between the centers of your eyes, specifically measured from the center of one pupil to the center of the other. The PD is measured in millimeters (mm) Most adults have a PD between 54mm to 74mm. This value is required by eyeglass manufacturers in order to properly make your glasses so that the centers of the lenses are placed for optimal focus and quality of vision. Glasses made with an inaccurate PD can cause a variety of problems such as headaches and blurry vision.