When measuring PD for PALs, what type of PD should you be measuring?

• A. Binocular PD
• B. Monocular PD
• C. Interpupillary PD
• D. Average PD

Answer: (B)

Fitting progressive addition lenses requires centering the lens per eye, not as a single average. Measuring monocular PD ensures each eye’s optical center lines up with its own pupil, so the progressive corridor and near addition are placed correctly for both eyes. If you used a binocular or average PD, one eye could be decentered relative to its pupil, causing peripheral distortion, eye strain, or uncomfortable transitions between distance and near zones. Interpupillary or average PDs don’t provide the per-eye precision needed for PAL centration, whereas monocular PDs give the accurate per-eye measurements essential for comfortable, accurate vision.