(TRI-foh-kul): Eyeglass lens that incorporates three lenses of different powers. The main portion is usually focused for distance (20 ft.), the center segment for about 2 ft., and the lower segment for near vision (14 in.). 20/20: Normal visual acuity. Upper number is the standard distance (in feet) between an eye being tested and the Snellen eye chart; lower number indicates that a line of letters or symbols of a specific size can be read from 20 feet away.
A type of spectacle or contact lens design that includes three focal areas: usually a reading lens, a lens for faraway viewing, and a lens for mid-distance viewing.
eyeglass lens that incorporates three lenses of different powers. The main portion is usually focused for distance (20 ft.), the center segment for about 2 ft., and the lower segment for near (14in.). 20/20 - normal visual acuity. Upper number indicates that a patient can see standardized symbols on a chart 20 ft. away; lower number indicates that the same symbols can be seen at 20 ft. by an eye with normal optical system.
lens with three perspectives of vision
A lens with three focusing points; as, distance, intermediate and reading.
A lens design that has three focal areas: a lens for close work or reading, a lens for mid-distance viewing or arm's length, and a lens for faraway viewing or driving.
n. having three focal lengths; having one section that corrects for distant vision, a second section that corrects for middle vision, and a third that corrects for near vision, as an eyeglass lens.
A lens having two added powers in the form of a segment or segments.
Trifocals are eyeglasses where the lenses have 3 regions to correct 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. The intermediate addition is normally half the reading addition.