What is BIFOCAL?

With a double focus. Applied to a system of lenses or spectacle- glasses with two foci, chiefly used for the correction of presbyopia, when there is at the same time an error of refraction for distant vision. The distance lens is above that for near work. These are sometimes. B. Distance Lens. A. Reading Lens, cemented to the Distance lens. called Pantoscopic lenses, and also Franklin spectacles, because the device was first made by Benjamin Franklin. They are also called Cement lenses, because now made by cementing the lower segment to the distance lens.

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Definition of  BIFOCAL