Many of us think our eyesight is better than it is. Research shows that one in three people who believe their sight is fine would fail a standard eye test. Unless we're walking into lampposts, we're happy to assume our eyes are in good shape.
"If it's a very slight problem, then you might only become aware of it during visually demanding tasks, usually at work," says Dr Susan Blakeney of the College of Optometrists. "Even then, the main symptom could be a headache, which you don't automatically associate with eyes."
Teachers wading through piles of homework can sorely test their sight. "At least with a computer screen you can change the font or make it bigger,"
says Dr Blakeney. "If children have terrible handwriting, then you're stuck with it."
Fiona Hart, a new teacher in Surrey, found that an evening's marking often left her with tired eyes and a headache. "I put it down to concentrating hard," she says. Then one day she couldn't read the whiteboard. "I got my eyes tested and found I was slightly short-sighted," she said. Fiona now wears glasses and the soreness and headaches have gone. But even if your vision is fine, long hours in front of a computer can cause eyestrain.
"Eyes aren't designed to focus at the same distance for long periods," says Dr Blakeney. "The eye muscles won't work as efficiently and can start to ache."
A professional check every two years is best and according to the National Union of Teachers, even "occasional" computer users are entitled to a regular eye test at their employer's expense.
"Taking care of your eyes is a good investment for the future - healthy sight will improve your quality of life," says Dr Blakeney
Stop the strain
During close work look up regularly and take a break every 20 minutes.
Get the lighting right. Eyes tire if it's too dark, and glare or reflection causes fatigue.
Customise computer settings: use the right font and size. Ensure the screen is clean, and positioned just below your eye-line.
Carrots really do help you see in the dark. Blueberries, hemp seed oil, and kiwi fruit are also said to be good for the eyes.