The center of the 'box' that isn't always at the optical center is called what?

• A. A Measurement
• B. Box Center
• C. Frame PD
• D. Geometric Center

Answer: (D)

The center of the frame’s box is called the geometric center. This point is the midpoint of the frame’s overall box, not necessarily where the lens’s optical center sits. The optical center is the point in the lens that aligns with the wearer’s line of sight, and because frames can be tilted, decentered, or shaped asymmetrically, that optical center often ends up away from the box’s geometric center. So the box center is a fixed geometric reference, while the optical center is determined by the lens and how it’s positioned in front of the eye. The other terms don’t describe this frame-reference center: a generic measurement isn’t specific, “box center” isn’t a standard term, and Frame PD relates to pupillary distance rather than the box’s center.