I've heard about bifocals eyeglasses and progressive eyeglasses,I know little about trifocal eyeglasses,Is there anyone can do me a favor?

Trifocal eyeglass lenses have an additional ribbon-shaped lens segment immediately above the near seg for seeing objects in the intermediate zone of vision — approximately 18 to 24 inches away.

This intermediate segment provides 50 percent of the added magnifying power of the near seg, making it perfect for computer use and for seeing your speedometer and other dashboard gauges when driving.

Trifocals are especially helpful for presbyopes over age 50, who have less depth of focus than younger presbyopes, who may still be able to see objects at arm's length reasonably well through the top part of their bifocals. As with bifocals, the most popular trifocals have a flat-top (FT) design, with the near and intermediate segments being 28 mm wide.

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