What Are Bifocal Glasses and Trifocal Glasses?
Bifocals are two prescriptions combined into a single lens. Trifocals are three prescriptions combined into one lens. Bifocals were originated by Benjamin Franklin in the 18th century when he cut the halves of two spectacle lenses and fitted them into one frame. Bifocals are needed because the distance glasses do not suffice to focus sufficiently for near. As age increases, (in India 38-40 years is the presbyopic age) reading glasses are required to read at a comfortable distance. Rather than taking out the distance glasses and putting on near glasses each time, a person who wishes to work at the near point could use the lower segment comfortably. There are various types of bifocals available, from the round-top bifocal, flat-top bifocal to the executive bifocal. What would be the basis of selection of a type of bifocal? Depending upon the occupational needs, a type of bifocal is selected. A salesman, who has mostly outdoor work and very little reading to do, would have a small round-t
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- What Are Bifocal Glasses and Trifocal Glasses?
