One of the main problems with bifocal and trifocal lenses is the problem of eye fatigue. It is difficult to switch from one focusing power to another. It can make your eyes tired, and it can even lead to a headache, sore neck and sore back.
A recent variation of bifocals and trifocals are called no-line lenses or progressive lenses. No-lines provide a smooth transition from focusing on nearby to focusing on distant objects because they do not have a distinct line which separates the focusing powers. Instead, a gradual change in power allows the wearer to focus on objects at all distances. Distant objects are viewed through the upper portion of the lens, while near objects are viewed through the middle or lower portion of the lens. These are also great for computer users.