American Board of Ophthalmology (ABO) Practice Exam

Which of the following factors does NOT affect the amount of jump in a bifocal lens?

1. The seg inset

2. The frame size

3. The lens material

4. The lens thickness

The correct answer is: The seg inset

The amount of jump in a bifocal lens primarily relates to how the prescription and position of the segments are designed. Jump refers to the vertical displacement that occurs when moving from the distance portion of the lens to the near segment. The seg inset, which involves how far the segment is inset from the optical center for optimal viewing, does not affect the amount of jump. Jump is predominantly influenced by the height of the segment, the curvature of the lens, and the distance between the pupil and the segment. In contrast, the frame size influences the jump because larger frames can potentially lead to a greater perceived jump due to the increased vertical distance between the optical centers. Lens material can influence the overall thickness and curvature, which can also indirectly affect the jump through changes in the optical configuration. Finally, lens thickness can contribute to the weight and construction of the lens, which may influence the position and stability of the segments. The seg inset being the only factor that does not aggravate or alter the jump directly makes it the correct answer in this context.