As the name indicates, bifocal reading glasses are glasses with two distinct optical powers. These glasses are usually prescribed for presbyopic individuals who also need a correction for myopia or astigmatism. Being popular nowadays, bifocal reading glasses can be dated back to around 1760, when the America statesman and investor Benjamin Franklin first developed them. Suffering presbyopia and nearsightedness, the great man thought it was really inconvenient to switch between two pairs of prescription glasses. Even if there are still serious historians suggesting that there were others who had preceded Franklin in the invention of bifocal reading glasses, Franklin is certainly among the first to wear bifocal glasses.
An original version of bifocal reading glasses was made of the most convex lenses for close viewing in the lower half of the lens and the least convex lenses on the upper half. In the early 20th century, a new design using two separate lenses cut in half and combined together was invented. However, such a design had long been associated with a number of complications such as fragileness. At the end of the 19th century, Dr. John developed the technology of lens fusing, with which the two separate half lenses could be fused together appropriately. Nowadays, the production of bifocal reading glasses is further different. Manufacturers of bifocals usually mold a reading segment into a primary lens. In addition, such a reading segment is available in a variety of shapes and sizes, offering customized versions for individuals with specific occupations. Currently, the most popular design is the D-segment with 28mm wide.
Even if there are some design variations of bifocal reading glasses, the basic style has remained untouched since the first pair. The upper section of a bifocal lens is for distance vision and the bottom part for viewing near objects. This fundamental design is based on the fact that most people will tilt their heads slightly upwards in order to see a distant object and downwards for a near focus. This basic design enables presbyopia folks to benefit from those bifocal reading glasses in a natural way. In fact, bifocal glasses are being enjoyed by a large number of individuals with both presbyopia and nearsightedness. Bifocal glasses are generally considered healthier for people’s eyes, because the eyes can always see through the correct prescription lens. It is estimated that approximately 4 million Americans develop presbyopia each year, most of which are between 35 and 50 years old.