What is required when the wearer's P.D. is less than the frame P.D.?

When the wearer's pupillary distance (P.D.) is less than the frame's P.D., a positive face form is necessary to ensure proper lens positioning and alignment with the wearer's visual axis. Positive face form involves the frames being curved outwardly at the temples, which helps bring the optical centers of the lenses closer to the wearer’s pupils.

This adjustment is crucial because if the optical centers of the lenses are too far away from the wearer's pupils, it can lead to visual discomfort, reduced optical performance, and an overall suboptimal wearing experience. Positive face form accommodates the anatomical position of the eyes, particularly when the frame is designed for wider P.D. than the wearer has.

On the other hand, negative face form would move the lens centers further apart rather than aligning them properly with the wearer’s eyes, making it unsuitable for this scenario. Retroscopic tilt and pantoscopic tilt refer to angles at which the lenses are tilted vertically and horizontally and do not address the specific issue of aligning the optical centers with the wearer's pupils.