Bifocal Lens

Invented by : Benjamin Franklin

Invented in year : 1784

Bifocals are eyeglasses with two distinct optical powers. The are composed of a lens having one section that corrects for distant vision and another section that corrects for near vision. They are also known as 'Benjamin Franklin Bifocals' or 'Benjamin Franklin Glasses'. Bifocals are most commonly prescribed to people with presbyopia  who also require a correction for myopia, hyperopia, and/or astigmatism. Original bifocals were designed with the most convex lenses (for close viewing) in the lower half of the frame and the least convex lenses on the upper. Up until the beginning of the 20th century two separate lenses were cut in half and combined together in the rim of the frame. The mounting of two half lenses into a single frame led to a number of early complications and rendered such spectacles quite fragile.

History

In 1784, Benjamin Franklin developed bifocal glasses. He was getting old and was having trouble seeing both up-close and at a distance. Getting tired of switching between two types of glasses, he devised a way to have both types of lenses fit into the frame. The distance lens was placed at the top and the the up-close lens was placed at the bottom. John Isaac Hawkins, the inventor of trifocal lenses, coined the term bifocals in 1824 and credited Dr. Franklin.

Development in the invention of Bifocals

Towards the end of 19th century Louis de Wecker devised a method to fuse the lenses together. This method was later patented by Dr. John L. Borsch, Jr. in 1908. Just a couple years later, the first single piece bifocal lens appeared.

Bifocal lenses evolved rapidly throughout the 20th century. In the 1980s the first bifocal contact lenses appeared.

Multifocals were later developed which let's one focus through different prescriptions at different distances through the same lens - hence the name. Bifocals (meaning a lens with two points of focus — usually one for distance and one for near) are the most commonly prescribed multifocal lenses.

Role of Bifocals in the development of human life

• It  is because of the invention of Benjamin Franklin that people with eye problems are able to read comfortably.

• The invention has laid the foundation for further research which continues to eliminate the limited field of vision in current bifocals.

• New materials and technologies may provide a method which can selectively adjust the optical power of a lens. Researchers have constructed such a lens using a liquid crystal layer sandwiched between two glass substrates.