Trifocal

Trifocal refers to a type of corrective lens with three regions correcting for distance, intermediate (arm's length), and near vision. They are mostly used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition.

History

The first patent for trifocal lenses was granted to inventor Louis de Wecker in 1906. However, the concept of trifocal lenses was first introduced by Benjamin Franklin, who developed the bifocal lens.

Design

Trifocal lenses are designed with two visible lines that separate the three different vision areas. The top area is for distance vision, the middle area is for intermediate vision, and the bottom area is for near vision. The size and placement of these areas can be customized based on the wearer's visual needs and lifestyle.

Types

There are two main types of trifocal lenses: flat-top and executive. Flat-top trifocals, also known as D-segment trifocals, are the most popular. They have a D-shaped near segment that is flat on top and round on the bottom. Executive trifocals, also known as Franklin trifocals, have a near segment that extends across the entire width of the lens.

Usage

Trifocal lenses are used by individuals who require correction for near, intermediate, and distance vision. They are often prescribed for people with advanced presbyopia, a condition that affects the eye's ability to focus on close objects. Trifocal lenses can also be used to correct for astigmatism and other refractive errors.

See also

• Bifocal lens
• Progressive lens
• Corrective lens
• Presbyopia
• Astigmatism

References

Trifocal Resources
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