The development of bifocal glasses

In the history of bifocal glasses, Benjamin Franklin has been generally credited with these glasses’ invention. Even if there are still historians doubting about whether he was the first to invent bifocal reading glasses, Benjamin wrote in his letters of correspondence that he invented these glasses independently. And this great man was surely among the first to use bifocal lenses. At the beginning of the 20th century, two separate lenses were cut in half and combined together in the rim of the frame. This is typical and traditional bifocal design which is called Franklin or Executive bifocal. The basic feature of these bifocals is that there is a line going all the way across the entire width of the lens. Not so long ago, all presbyopic patients had to wear this original version of bifocal reading glasses. Of course, these glasses have helped them a lot.

Lens technology has never stopped its progression. This is also the case in the world of bifocal reading glasses. As a typical and the most common type of multifocal eyeglasses, bifocal glasses are now available in a few of lens designs. Some of them are designed for special occupational use. As the name shows, a bifocal lens has never changed its nature that there are basically two different lens powers or two focal points. The typical design involves one power for distance and the other for near. These glasses are really needed by people who require some visual correction in order to read or see things nearly.

Nowadays, bifocal glasses that mold a reading segment into a primary lens are the majority in the market. The Franklin style can be seldom seen now. The commonest design is D segment, which is also called half-moon, flat-top or straight-top. The added reading segment can be in other shapes, like round and narrow rectangle. All these modern designs actually work in the same way. Different shapes or positions of the reading segment are generally aimed to provide customized visual correction for people with particular occupations.

C: Bifocal glasses have different lens designs after so many years’ development. The original Franklin style has been diversified by adding different shapes of reading segment, like half-moon, round and narrow rectangle.