A small portion of the bifocal eyeglass lens is reserved for the near-vision correction. The rest of the lens is usually a distance correction, but sometimes has no correction at all in it, if you have good distance vision. Generally, you look up and through the distance portion of the lens when focusing on points farther away and look down and through the bifocal segment of the lens when focusing on reading material or detail work up to about 18 inches away. The Executive style is one of the most common types of trifocals. The intermediate zone is shown in green.
Computer terminals are generally in the intermediate zone.
Motorists who need to be able to see in the distance to drive as well as to see the gauges on the dashboard and to read a map also would benefit from a trifocal lens in order to see things in the distance, the intermediate and the near areas. Flat-top and Executive lens styles are the most common trifocals. Bifocals are typically placed so that the line rests at the same height as the wearer's lower eyelid. Trifocals are fitted a bit higher, with the top line of the intermediate area placed even with the pupil . As a bifocal wearer drops his eyes downward in order to read, the eyes naturally seek out the near-vision portion of the lens.