As the eye crosses from the distance portion of a bifocal lens to the reading segment the image often appears to jump. This can be especially disconcerting on stairs and kerbs and could contribute to an accident if the wearer hasn't been forewarned. Round segment bifocals suffer from jump the most, and the larger the segment the worse it is. Large D-segment bifocals (D40), and so called Executive Bifocals have no jump. Curved top C-segment bifocals probably offer the best compromise between jump, cosmetic appearance and overall ease of use. | |