Which PD type is used during PALs measurement?

• A. Binocular PD
• B. Monocular PD
• C. Interpupillary Distance PD
• D. Near PD

Answer: (B)

For PALs measurement, the position of the progressive corridor must be aligned to each eye individually. This requires monocular PD, which records the distance from the center of each pupil to the bridge for each eye. Because each eye can have a slightly different PD and the frame’s tilt and wrap influence how the lens is perceived, using one combined distance for both eyes can shift the progressive zones off the visual axes. Measuring monocular PD ensures the progressive powers line up correctly with where each eye is looking and that the corridor starts and ends where the wearer needs them.

Binocular PD gives the overall distance between the pupils but doesn’t account for asymmetry between eyes, so it isn’t sufficient for precise PALs fit. Near PD is used for near tasks and reading configurations, not for accurately placing the progressive corridor during the initial PALs measurement. Interpupillary distance PD is another term for the overall binocular distance, which again misses the eye-by-eye precision needed forPALs.