What measurement determines the distance between the optical centers of spectacle lenses?

The correct answer is "Pupillary Distance," which measures the distance between the pupils of the eyes. This measurement is essential for properly aligning the optical centers of spectacle lenses with the wearer's pupils to ensure optimal vision correction. When lenses are positioned correctly in front of the eyes, visual clarity and comfort are enhanced, reducing visual distortions and strain.

In the context of spectacle fitting, the pupillary distance ensures that the prescribed lenses are centered over the eyes, which is important for bifocal or progressive lenses where precise alignment can greatly affect performance. While interocular distance might also refer to a similar measurement, it is not the standard term used in eyecare settings. Similarly, optical center distance and frame width refer to different parameters in the lens fitting process, such as the design of the frame or the lens itself, rather than the critical alignment necessary for effective vision correction.