Some people of an age of forty or older may have such an experience that when they tried to buy a pair of reading glasses, the seller or retailer recommended a pair of bifocal reading glasses which was relatively more expensive.
In fact, these bifocal reading glasses have been in wide use for many years.
A large number of elder individuals have to rely on these devices while carrying out some of their daily activities including recreations.
However, there may be still lots of users who do not know or have little information of two points of these glasses.
One is the origin and the other is the exact function.
The most widely recognized origin of bifocal reading glasses is that they are invented in 1794 by Benjamin Franklin who was one of the founders of the United States.
This great statesman had trouble seeing both up close and at a distance when he was getting old.
During a long time, he had to use periodically two pairs of prescription eyeglasses, one for close vision and the other for distance view.
Of course, this kind of practice was very inconvenient when he wanted to switch visual ranges on a daily basis.
A great man is always easier to be driven to develop an alternative to the unsatisfying, current solution.
Benjamin was at that time also a great inventor.
The first pair of bifocal reading glasses was created by him by having both types of the lenses fit into a single frame.
That was the same design of bifocal reading glasses that is widely seen today.
The past two centuries have never witnessed a significant change in the basic design.
Till now, the function of this kind of magic spectacles is quite clear that they can enable a wearer to see both near and distant objects clearly.
This is achieved by combining a positive power and a negative power in a single lens.
A bottom part of the lens is usually made for near viewing and the upper section is for distance vision.