What type of PD is measured when fitting progressive addition lenses?

• A. Monocular
• B. Binocular
• C. Inter Pupillary Distance
• D. Segment PD

Answer: (A)

When fitting progressive addition lenses, you need to center the optical zones for each eye individually. This requires monocular PD measurements—one PD for the right eye and one for the left eye. Monocular PD ensures the progressive corridor aligns with each eye’s pupil as the eyes look straight ahead and during reading, accommodating any asymmetry between the eyes. Using a single binocular PD would not account for these differences and could misplace the progressive zones, leading to peripheral distortion or discomfort. Segment PD is used for bifocals with a visible segment line, not for progressively updated lenses, and Inter Pupillary Distance is the general term for PD, but the specific measurement needed for PALs is the monocular PD.