Bifocal and Trifocal Lense
Bifocals and trifocals lenses have been around for many years to help us over age 40 deal with the normal age-related loss of near vision.
History Of Bifocals and Trifocals
Benjamin Franklin, the early American statesman and inventor, is credited with creating the first multifocal lense for eyeglass. Prior to Franklin’s invention, anyone with presbyopia had to carry two pairs of eyeglasses — one for seeing distant objects and one for seeing up close.
Sometime around 1780, Franklin cut two lenses in half (one with a distance correction and one with a correction for near) and glued them together. This first-known bifocal lens, with a line extending across the entire width of it, separated the corrections for distance and near. Initially called the Franklin bifocal, the lens design later became known as the Executive bifocal.
Modern Bifocal and Trifocal Lens Options
Today, Person can select from many bifocal and trifocal lens designs, depending on your age and visual needs. There are even special bifocals and trifocals designed for glasses for computer work and other tasks that take place at the intermediate range.
As their name suggests, bifocal eyeglass lenses have two lens powers — one for distance and one for near. The lower half of a bifocal lens contains the near segment for reading and other close-up tasks. The rest of the lens is usually a distance correction, but sometimes has no correction at all in it, if you have good distance vision.
Trifocal eyeglass lenses have an additional ribbon-shaped lens segment immediately above the near seg for seeing objects in the intermediate zone of vision — approximately 18 to 24 inches away.
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