Trifocal glasses are invented to solve certain problems, such as myopia, hyperopia, or even amblyopia. Lenses of trifocal are devided into three segment dirstrics. Wearers can see clearly with these three powerzones. And sometimes, trifocal glasses will do more help for computer work, reading newspaper and so on. People who are over the age of 50 are really in need of such glasses. If you want to buy one, cheapprescriptionglasses.net is a good place for you to buy one.