In progressive lens fitting, which type of PD is commonly measured?

In progressive lens fitting, which type of PD is commonly measured?

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

Answer: (A)

The key idea is per-eye centration. Progressive lenses have a gradual power change across the lens, so aligning the optical center of each eye with its respective pupil is crucial for comfortable vision at near, intermediate, and distance. Measuring monocular PD gives you a separate distance for each eye, ensuring the progressive corridor sits correctly for both eyes rather than relying on a single shared value. Using a single binocular PD can misplace the progressive zones if the two eyes aren’t perfectly symmetrical, leading to blurry or unstable vision when looking through the wrong part of the lens. Segment PD is about locating bifocal segments, not the gradual zones of progressives, so it isn’t the measure that ensures proper progressive lens alignment. Interpupillary distance is the general distance between pupils and may be used as a starting figure, but progressive fitting relies on monocular PD for accurate per-eye centration.

The key idea is per-eye centration. Progressive lenses have a gradual power change across the lens, so aligning the optical center of each eye with its respective pupil is crucial for comfortable vision at near, intermediate, and distance. Measuring monocular PD gives you a separate distance for each eye, ensuring the progressive corridor sits correctly for both eyes rather than relying on a single shared value. Using a single binocular PD can misplace the progressive zones if the two eyes aren’t perfectly symmetrical, leading to blurry or unstable vision when looking through the wrong part of the lens.

Segment PD is about locating bifocal segments, not the gradual zones of progressives, so it isn’t the measure that ensures proper progressive lens alignment. Interpupillary distance is the general distance between pupils and may be used as a starting figure, but progressive fitting relies on monocular PD for accurate per-eye centration.