What does the Pupil Distance (PD) measurement reflect?

The Pupil Distance (PD) measurement reflects the distance between the center of the pupils of the eyes. This measurement is crucial in ensuring that optical lenses are correctly aligned with the wearer’s visual axis, providing optimal vision and comfort. Accurate PD measurement is essential for proper lens placement in frames; if the lenses are not centered over the pupils, it can lead to visual distortions or discomfort.

In the context of the other options, the height of the lens pertains more to the vertical dimension of the lens profile, which does not directly affect the horizontal alignment crucial for PD. The width of the frame relates to the overall size and fit but does not specifically address the positioning of the optical center of the lenses. Similarly, the length of the temple refers to the arm that rests on the wearer's ears and is unrelated to visual alignment. Therefore, focusing on the correct alignment of the lenses with the PD directly impacts the craft of lens fabrication and fitting.