While reading glasses may be fine for reading books and papers at distances up to 18 inches away from the eyes, they may not be well-suited to computer work. No single lens prescription can meet all needs, which is why many office workers turn to dedicated computer-screen bifocals. These glasses have a mid-range prescription on the upper portion of the lens and a reading prescription on the bottom part. This setup enables those with desktop computers to shift their gazes easily from the computer screen to printed material, and back again. As with other types of bifocals and trifocals, computer-specific bifocals can be outfitted with no-line progressive lenses, which give co-workers little clue that they are bi- or trifocals. Anti-glare coatings on prescription work glasses help diminish on-screen glare and brightness of overhead lights. General purpose bifocals are not designed for computer work as they force the wearer to tilt the head back in order to focus on the screen while looking through the lower segment of the lenses. A forced position like this can cause neck and shoulder pain and even arm and low back pain.