Definitions for "Trifocals"
Keywords:  eyeglass, vision, pal, distance, near
Eyeglass lenses having three areas of viewing, each with its own focal power. Usually, the upper portion is for distance viewing, the lower for near and the middle for the distance in between.
Eyeglasses that accommodate three different viewing areas to provide clear vision at near, distance and mid-range; have two well-defined visible lines separating the viewing zones.
a lens design with three areas to look through, the top area is for distance vision, the central area is for intermediate vision, and the lower part is for near vision; each division is separated by a line which is sometimes in the way; a more natural (no line) alternative may be the PAL.