Starting around the age of forty or so, the ability to focus on closer objects decreases - books and newspapers have to be held farther away to bring them into clear focus. This is probably the first sign of the condition called presbyopia from Greek words meaning old man's eyes. Another sign of presbyopia is that people's ability to refocus quickly between near and far objects decreases. Most people over forty require the vision correction for reading or performing other near tasks. The most common correction that allows for near vision without compromising far vision is a bifocal lens. The bifocal lens has an upper segment that affords clear vision in the far distance and a lower segment used for reading or viewing close objects.However, the conventional bifocal correction gives visual comfort for a presbyopic person is not recommended for working with a computer. As mentioned before, wearing bifocal glasses forces a computer user to tilt the head back to focus on the screen through the lower part of the bifocal lenses. Such a forced position can cause neck, shoulder and back pain. In some people it can also result in localized tingling or 'pins and needles' sensations in the hands, wrists, or forearms.
