Nowadays, many children spend hours a day looking at computer screens or other digital   products. Some eye care doctors say all the screen time has caused more children to have what they call computer vision syndrome  . Nathan Warford is an optometrist in the US. He says he has seen more children having eye problems. "More children come into my office because their parents have noticed that they have headaches  or red eyes, or because their degree of short-sightedness appears to be increasing  very fast and they're worried," he said. Dr. Warford says part of the problem is that even if their eyes start to feel uncomfortable or they start to get a headache, some children don't tell their parents, because they don't want their games or the computer to be taken away. Another part of the problem is that people blink   less often when they look at the screen.A person who uses a computer or a digital product blinks about a third as much as we normally  do in everyday life. If eyes can't stay wet or are too tired, they will not be protected like normal. People blink about  _  as they normally do when they use computers.
a third as much two thirds as much half as much as much