Multifocal eye wear provides correction for reading and distance vision.
Spectacles that provide more than one correction in the same pair of eye wear are typically fitted with progressive lenses or bifocal lenses. Each serves a similar purpose, but there are differences both functionally and aesthetically.
Applications
As people age, they frequently find that their arms are not quite long enough to read or view objects close up---a condition called presbyopia. Other medical causes resulting in the need for progressive or bifocal lenses include over convergence, when the vision becomes blurred because the eyes move too far inward in the attempt to see up-close objects.
Bifocals
Bifocal lenses are the most common prescription for up-close and distance vision correction in the same eye wear. They can be identified in most cases with a line where the two prescription curvatures abut one another. This lower-cost option is the most popular multi-focal lens.
Progressives
Progressive addition lenses, also known as no-line bifocals or progressives, provide correction for more than one visual disorder in the same eye wear without the telltale line of a bifocal lens and with a smoother, more natural transition. Progressive lenses provide zones of vision for near and far as well as a mid-distance as needed for activities such as computer work.
Considerations
There are a variety of progressive lens options, each with its own design focus with zones of clarity and distortion based on the surface of the lens. New users sometimes experience "swim and sway" in the adaptation process as the eye becomes accustomed to using progressives.
History
Benjamin Franklin invented the first bifocal lens in the early 1760s.
Tags: bifocal lens, correction same, distance vision, more than, same wear