Trifocal lenses
（重定向自Trifocal lens）
Trifocals, patented in 1827 by John Isaac Hawkins, are eyeglasses with lenses that have three regions which correct for distance, intermediate (arm's length), and near vision.
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.