Bifocals

Bifocals are eyeglasses that have two sets of corrective lenses for people with impaired vision for both close and long distance viewing.

This form of corrective lens set was invented by Benjamin Franklin who needed two sets of glasses to deal with each aspect of the above kind of impaired vision.

This proved cumbersome, but the solution presented itself when he realized that when a person views something at close range, they usually look down and the reverse is true when they view at a distance. Taking advantage of that fact, he designed bifocals with the lenses for close viewing in the lower half of the frame and the distance viewing lenses on the upper.