What act involves positioning a lens to align with prescription specifications?

Centration is the process that involves positioning a lens to align it accurately according to prescription specifications. This step is crucial because the effectiveness of the glasses relies on the optical centers of the lenses matching the visual needs of the person wearing them. Proper centration ensures that the optical axis of the lenses coincides with the pupil centers when the glasses are worn, which is vital for clear vision and comfort.

In this context, while blocking refers to the method of securing a lens in place for edging, and edging is the actual shaping of the lenses to fit the frames, neither of these processes specifically addresses the precise alignment necessary for optimal vision. Centroiding, on the other hand, pertains more to finding the geometrical center of a lens rather than the alignment of its optical properties, further emphasizing the specific role that centration plays in optical practices.