Entering your correct pupillary distance (PD), the distance between your pupils, measured in millimeters, is as important as entering your correct prescription when you fill out the prescription form.

 The PD tells the manufacturer of the eyeglasses where to place the optical center on the lens, which is where the wearer looks through the lens.If the PD is not accurately placed on the lenses, the wearer may have difficulty focusing both eyes together.

 A single PD would be provided by one number and is the measurement of the center of one pupil to the center of the other. An average range of adult PDs is between 54 and 74 mm. An average range of a child’s PD is between 43 and 58 mm.

 A dual PD would be provided with two numbers and would appear and is the measurement of each pupil center to the center of the bridge of the nose, in millimeters. Dual PD appears in the following format: "33/31".

Watch this video on how to measure your own PD: