Does reading in dim light ruin your eyes?

Monday, July 10, 2006
This tale has been around for as long as our grannies have — read in dim light and you'll ruin your eyes. But where did it come from?

Dr Katrina Schmid is a Brisbane-based research scientist and optometrist: "I think that would have come about from years gone by when we only had candles to read by, and that would obviously be a very low light level. You can still see and read under that light level because our system's so flexible, but you would've been working really hard."

But can overworking your eyes actually ruin them?

There's only one way to find out. Our reporter Michael Slater, who has good eyesight and doesn't need to wear glasses or contacts, has decided to put it to the test.

Michael's eyes will be tested under bright light and dim light to see if there's any change in the way he focuses.

Dr Schmid has just the machine to do it: an auto-refractor, which can measure whether the eye is focussing properly on an object.

The good doctor will look at Michael's focussing ability under dim light versus bright light.

She'll look at how his eyes focus on a page and measure the time required to focus into the distance from looking up from a page.

All Michael needs to do is sit still and focus on some long-distance and near distance objects for three minutes.

When the lights were fully on, Michael was able to change focus between long distance and near distance objects without difficulty. However, when he runs through the test again, this time in dim light conditions, things get a lot harder and the results prove telling.

Michael's "focusing is inaccurate relative to the bright light conditions for far away and up close," says Dr Schmid.

Michael's eyes simply can't focus as accurately in dim light as they can in bright light.

Why? The retina is the part of the eye that detects light, it's covered with cells called cones which see colour, but only when the light is bright. As we move from bright to dim light, the pupil enlarges to maximise the amount of light coming in. Our cones are still working, but not as well as in bright light. Smaller letters are now more difficult to read so we compensate by bringing the text closer to our eyes. Therefore, you get into a cycle where it's getting closer and closer and it's getting harder and harder so you get more and more tired and eventually you'll get headache, tired eyes and give up.

Reading in dim light is not in itself going to ruin your eyes. But if you bring the book closer to focus better, then this is the thing that's going to cause problems, with the possibility of exacerbating short-sightedness.

"So the closer something is held, the nearer it is, the harder it is to focus accurately on it and the more likely you are to under-focus, not focus on it correctly and for it to cause short-sightedness," says Dr Schmid.

  • Wear glasses? There have been some studies done in Singapore where they've taken kids who are short sighted and those who aren't and they've measured their IQ and the IQ of the short sighted kids is actually higher.

  • Do kids damage their eyes if they sit too close to the telly? If they sit approximately 50 centimetres away they'll very quickly get eye fatigue and if they stay there for long periods, a certain percentage of kids will be susceptible to developing myopia, or short sightedness. For anyone watching telly, the ideal watching distance is between 1.5 metres and two metres. You should also make sure not to rely on the TV as the only light source in the room.

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