Where were the first bifocal glasses invented when and how they changed since pair?

The first bifocal glasses were invented in the United States in the late 18th century. They were created by Benjamin Franklin, who was a printer, scientist, and statesman. Franklin was in his late 70s when he invented bifocals, and he found that he was having difficulty seeing both near and far objects. He decided to try using two pairs of glasses, one for reading and one for distance vision, but he found that it was inconvenient to have to switch between them. He then came up with the idea of creating a pair of glasses that had two different prescriptions, one for reading and one for distance vision.

Franklin's bifocals consisted of two lenses that were joined together by a metal frame. The top lens was for distance vision, and the bottom lens was for reading. The lenses were positioned so that the reading lens would be in front of the pupil when the wearer was looking down, and the distance lens would be in front of the pupil when the wearer was looking straight ahead.

Bifocal glasses quickly became popular, and they have remained one of the most common types of corrective lenses ever since. They have undergone some changes over the years, but the basic design has remained the same. Modern bifocal lenses are typically made from plastic or glass, and they can be coated with a variety of finishes to improve their durability and scratch resistance.

Bifocals are still a popular choice for people who need correction for both near and far vision. However, there are now other options available, such as progressive lenses and multifocal contact lenses. Progressive lenses are similar to bifocals, but they have a gradual transition between the near and far vision prescriptions, which eliminates the visible line that separates the two lenses in bifocals. Multifocal contact lenses are also available, which provide correction for near, far, and intermediate vision.