Bifocals are eyeglasses, commonly prescribed for presbyopia, with two distinct optical powers.
Although there are arguments against him, Benjamin Franklin is generally credited with the invention of bifocals. After a correspondence between George Whatley and John Fenno it was thought that Franklin possibly invented the bifocals fifty years earlier than previously thought. Many inventions are worked on independently by many people and bifocals may have been the same, however, Franklin was definitely one of the first to wear them. In 1824, John Isaac Hawkins, who invented trifocal lenses, termed the coin bifocals and credit Dr. Franklin.
Bifocals are designed to have the most convex lens on the lower part of the frame and the least convex on the top. Until the 20th century two lenses were cut in half and put together. However, this led to many problems and caused the glasses to be very fragile. At the end of the 19th century Louis de Wecker created a process for fusing the two lenses together. Today the reading segment is molded into the primary lens.