Bifocal Lenses

“Bifocals lenses” is the common term for glasses that have two types of optical powers. Each optical power serves a different purpose: one corrects distance vision, the other improves the visually clarity of images that are in close range. From a distance, the lenses appear as if they are divided in the middle, or have a small segment in the bottom of the lenses that is separate from the rest. The purpose of bifocal lenses is to improve standard vision and aid in close-up vision for reading.

Purpose

Bifocals are commonly used to aid patients that are diagnosed with presbyopia, which is the inability to focus on objects that are in close range. The reason that bifocals have a dividing line in the middle  is that the main lens is designed to correct near or farsightedness, whereas the lower lens portion is more convex, and magnifies objects that are up close. Since people typically look down when reading, the more convex part is located in the lower portion of the lens.

History

Though there is no direct individual credit for the invention of bifocals, most historians typically consider Benjamin Franklin as the creator. Franklin never patented his inventions, so the official history of bifocals prior to his invention hasn’t been determined. It is believed that he started working on the idea of bifocals sometime before 1760, and with his final product being revealed in 1785. Dr. John Borsch, Jr. perfected the design by fusing the lenses together, and patented his creation in 1908.

Evolution

Though bifocals were an incredible benefit at the time of their invention, they posed a few problems like causing headaches and not adhering to intermediate vision. For this reason, the science of bifocals evolved into trifocals, which evolved into progressive lenses. Progressive lenses have no visible dividing line between the optical powers, and are considered the standard replacement for bifocals today