______ refers to the sudden displacement of an image at the bifocal line.

• A. Image jump
• B. Seg drop
• C. Prismatic shift
• D. Bifocal jump

Answer: (A)

When a bifocal lens has two distinct optical regions, the line between them creates a sudden change in the optical path as you look through it. The distance portion forms an image at one retinal location, while the near portion (with added power) forms an image at a different location. As your gaze crosses the bifocal boundary, light effectively comes through a different segment, causing the image to jump abruptly to a new position on the retina. This abrupt change in perceived image position at the bifocal line is the image jump.