What is the difference between a single PD and a dual PD?
Single PD is the distance in millimeters between one eye's pupil to the other.
Dual PD is the distance in millimeters from each eye's pupil to the center of your nose.
A single PD measurement is one number written in the PD section on your prescription like "62".
Dual PD measurement includes two numbers for different eye written as "31/31" or "OD PD: 31/OS PD: 31" which indicates that "right PD: 31/left PD: 31" ("OD" represents right eye and "OS" represents left eye).
• Range of Adult single PD: 54-74 mm
• Range of Child single PD: 43-58 mm
• Range of dual PD: 22-40mm