Long hours at the screen can cause 

Long hours at the screen can cause 41(ache) eyes, 42( blur) vision and headaches,experts say. In fact, eyestrain surpasses even wrist pain as the top physical 43( complain) among heavy computer users. When peering into the computer screen, the eye's focusing muscle is at constant tension. Like any muscle, it feels sore when b 44 (overload). And when someone spends a lot of time looking at something close, the eye muscle can get 45(stick) on the near-focus setting and have difficulty relaxing, leaving the person 46( temporary nearsighted, a condition called accommodative spasm(痉挛) that can last seconds or hours. The letters on the screen are not as clearly 47( define) as on a printed page. Take a magnifying glass to your monitor and you'll see the letters, each made up of pinpoint sources of light, have no sharp edges. But those liquid crystal display(LCD) monitors, like those found on laptop computers, are 48(easy) on the eyes because they display sharper images And studies have shown that when people are working on a computer, their rate of 49( blink) goes down by two-thirds, which can result in dry, stinging eyes.This is especially a problem for contact-lenses 50( wear).