For a Round seg (Ex Kryptok) bifocal used to calculate image jump, the distance between the optical center and the edge is referred to as which term?

For a Round seg (Ex Kryptok) bifocal used to calculate image jump, the distance between the optical center and the edge is referred to as which term?

• A. Radius of the segment
• B. Diameter
• C. Arc length
• D. Edge radius

Answer: (A)

In a Round segment, the distance from the optical center to the edge is the radius of the segment. Since the edge is defined by a circle, the straight-line distance from the center of that circle to any point on the edge is the radius. This radius is the key geometric parameter when calculating image jump for a Kryptok bifocal because it fixes how far the edge sits from the center, which determines when and how the image shifts as the pupil positions near the boundary. The diameter would be the full width across the circle, not the center-to-edge distance; arc length follows along the curved edge rather than the straight line to the edge; and “edge radius” isn’t a standard term.

In a Round segment, the distance from the optical center to the edge is the radius of the segment. Since the edge is defined by a circle, the straight-line distance from the center of that circle to any point on the edge is the radius. This radius is the key geometric parameter when calculating image jump for a Kryptok bifocal because it fixes how far the edge sits from the center, which determines when and how the image shifts as the pupil positions near the boundary. The diameter would be the full width across the circle, not the center-to-edge distance; arc length follows along the curved edge rather than the straight line to the edge; and “edge radius” isn’t a standard term.