Where is the optical center of a round segment located?

The optical center of a round segment is located in the geometric center of the segment. This point is crucial because it serves as the area through which light passes without deviation, ensuring that the wearer experiences the clearest vision when looking through the segment.

In the case of progressive or bifocal lenses that incorporate a round segment, locating the optical center at the geometric center allows for optimal alignment with the wearer’s line of sight. This design minimizes distortion and maximizes the effective power of that segment of the lens.

Understanding the positioning of the optical center helps in lens crafting and fitting, ensuring that visual correction is achieved effectively for the wearer. This principle is applicable in optical practices when selecting or fitting lenses for different visual needs.