Traditionally, bifocal Lenses are eyeglasses designed for people who need both near and far vision. The upper part of the lens is used for far distance and the lower half of the lenses helps in reading or doing other close work
With advancement in material science, progressive lenses or sometimes called "no-line bifocal lenses," eliminate the visible lines of traditional bifocals and trifocals and hide the fact that you need reading glasses... (This is good for old man like me.. people won't notice I am actually an old man..:cool: )
Progressive lenses are line-free multifocals that have a seamless progression of added magnifying power for intermediate and near vision. Progressive lenses provide a more natural correction of presbyopia than bifocal or trifocal prescription eyeglasses. With progressive lenses, you can look up to see clearly the far distance. You also can look ahead to view your computer in the intermediate distance and drop your gaze downward to read and do fine work comfortably in the near distance .
Images in the conventional bifocals and trifocals seem to "jump" as your eyes move past the sharply defined boundary between the far and near parts of the lens. With progressive lenses, the transition between lens powers within the lens is smooth and seamless, letting you change focus from distance to near and back again more comfortably, with no image jump.