Bifocals and trifocals have been around for many years to help people over age 40 deal with the normal age-related loss of near vision called presbyopia. Bifocal and trifocal lenses contain two lens powers (bifocals) or three (trifocals) to help restore a fuller range of vision and, in particular, to restore reading vision lost to presbyopia.
Benjamin Franklin, the early American statesman and inventor, is credited with creating the first multifocal lens for eyeglasses. Prior to Franklin's invention, anyone with presbyopia had to carry two pairs of eyeglasses — one for seeing distant objects and one for seeing up close. Sometime around 1780, Franklin cut two lenses in half — one with a distance correction and one with a correction for reading — and glued them together. This early bifocal, with a line extending across the entire width of the lens separating the distance and near corrections, was initially called the Franklin bifocal. It later became known as the Executive bifocal.
Today, you can select from many bifocal and trifocal lens designs, depending on your age and visual needs. There are even special bifocals and trifocals designed for glasses for computer work and other tasks that take place at the intermediate range.
In the following images, distance describes the area of the lens used for far vision, intermediate for arm's length and near for reading vision (about 16 inches away).