{{Short description|Lenses with three areas of distinct optical power}} {{Redirect|Trifocal|the tensor|Trifocal tensor}} Trifocal lenses|thumb '''Trifocals''' are eyeglasses with lenses that have three regions which correct for distance, intermediate (arm's length), and near vision. John Isaac Hawkins developed the trifocal lens in 1827.<ref>{{cite book|last1=Stein|first1=Harold A.|title=The Ophthalmic Assistant: A Text for Allied and Associated Ophthalmic Personnel|date=2012|publisher=Elsevier Mosby|location=Philadelphia|isbn=978-1-4557-3346-0|page=205|edition=9th|url=https://books.google.com/books?id=9I3oH--MnVYC&q=john%20hawkins%20ben%20franklin%20lenses&pg=PA205}}</ref>
Trifocals are mostly used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition. The intermediate addition is normally half the reading addition. So, for someone with a distance prescription of −4 diopters and a reading addition of +3, the reading portion of their trifocals would have a net power of −1, and the intermediate segment would be −2.5 diopters. {{cn|date=December 2025}}
Trifocal lenses are made in similar styles to bifocals, but with an additional segment for intermediate vision above the reading section. A common style is the 7×28 flat-top or D-shaped segment, 28 mm wide, with a 7 mm high intermediate segment. Larger intermediate segments are available, and are particularly useful for people who spend a lot of time using computers.{{cn|date=December 2025}}
Trifocals are becoming rarer as more people choose to wear progressive lenses.{{cn|date=December 2025}}
==See also== * Trifocal goggle
==References== {{Reflist}} {{Eyewear}}
Category:Corrective lenses Category:1827 introductions Category:Glasses
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