Long hours at the screen can cause aching eyes, blurred vision and headaches,experts say. In fact, eyestrain surpasses even wrist pain as the top physicalcomplaint among heavy computer users. When peering into the computer screen, the eye's focusing muscle is at constanttension. Like any muscle, it feels sore when overloaded. And when someonespends a lot of time looking at something close, the eye muscle can get stuckon the near-focus setting and have difficulty relaxing, leaving the persontemporarily nearsighted, a condition called accommodative spasm ( 痉挛 ) that can last seconds or hours. This is why after looking at a monitor all day, some computer workers complain thattheir distance vision is blurred when they attempt to drive home. The letters on the screen are not as clearly defined as on a printed page. Take amagnifying glass to your monitor and you'll see the letters, each made up ofpinpoint sources of light, have no sharp edges. But those liquid crystaldisplay (LCD) monitors, like those found on laptop computers, are easier on theeyes because they display sharper images. And studies have shown that when people are working on a computer, their rate ofblinking goes down by two-thirds, which can result in dry, stinging eyes. Thisis especially a problem for contact-lenses wearers. 1. ___ used to be the biggest physical problem that computer users had. A) Dry eyes B) Blurred vision C) Headache D) Wrist pain 2. Working hours before the screen will _____. A) impose too much burden on the eye’s focusing muscle B) bring about near-sightedness C) make it difficult for the user to learn driving D) magnify the letters on the screen 3. LCD monitors are better in terms of eye protecting because ___. A) they are more expensive B) they will not blur the user's eyes C) they bring about no eye problems D) they display letters with sharp edges 4. Dry, stinging eyes are caused by ___. A) lower rate of blinking of the computer user's eyes B) letters on the screen without any edges C) overburden on the focusing muscle D) a constant tension 5. Which group of people are most likely to get dry, stinging eyes? A) Drivers. B) Doctors. C) Glasses wearers. D) Contact-lenses wearers.