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Aug 29, 2010

Does reading in dim light damage your eyesight?

Conventional wisdom claims that reading in the dark wrecks the eyes. But children everywhere who love to read at night under the covers can rejoice, because this myth is FALSE.

Dim light might make it difficult for the eyes to focus, which can cause short-term eye fatigue, says Richard Gans, MD, FACS, an ophthalmologist with the Cleveland Clinic Cole Eye Institute. "But there is no scientific evidence that reading in the dark does any long-term harm to your eyes," Gans says.

Challenging visual work, such as reading in insufficient light, can also lead to short-term drying of eyes because you blink less often, Gans adds. Again, this is uncomfortable, but it doesn’t damage the structure or function of the eyes. You can use over-the-counter lubricating drops if dry eyes are a problem.

"People will say they've got tired eyes, burning eyes, strained eyes. But the problem might not actually be in the eyes. It might be caused by the muscles around the eye, the brow and so on. We don't really know", supports this point of view Brisbane optometry professor Nathan Efron.

But any eye strain should disappear within a day or so (at most) after you stop reading, or move somewhere with better light.

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Short-sightedness risk?

The notion that using our eyes in certain ways can sometimes cause them long-term harm isn't entirely nonsense, however.

There's "overwhelming" evidence that populations where people read a lot (or do a lot of other types of "close eye work" such as using a computer or sewing) have higher rates of myopia or short-sightedness, Efron says. (When you are short-sighted, your eyes focus well only on close objects, while more distant objects appear blurred. This is because light rays focus in front of the retina.)

No-one knows exactly why excessive reading causes this change. But focusing on close objects involves contraction of muscles controlling the shape of the eye's lens. And one possibility is that "this constant contraction may stretch the eyeball. So the eyeball changes shape and becomes more short-sighted," Efron says.

So reading a lot, whether in dim light or bright light, could encourage short-sightedness.

But when we read in low light, there may be a "double whammy" effect because other changes may happen that also encourage the development of short-sightedness - but in a completely different way.

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A theoretical concern

Dim light makes our pupils larger (to maximize light entering the eye). This means more light rays enter the eye through the edge of the pupil, which causes the light rays to be refracted (bent) differently and create a slightly blurred image at the edges of the retina. It's not enough for us to notice but it's thought that over time it may nonetheless act as a trigger for the eye to grow larger.

"The theory is that if you were to read in dim light for a few years, the eye will tend to grow slightly larger to make the peripheral images on the retina clearer. This enlargement of the eyeball however, may create a different problem in that it has the effect of making the eye short-sighted."

If the dim light effect does happen (no-one knows for certain yet because it has never been tested), it would be much more likely in children and young adults, whose eyes are still developing, than in older adults. And the changes could be permanent.

"It's theoretically possible in children and young adults until their early 20s," Efron says. "The eye is still growing and the tissues are more pliable, so they are more susceptible to long-term change."

So would Efron be worried if his own children made a habit of reading by torchlight under the covers?

"No, I wouldn't be overly concerned," he says. Not only is there no proof of any change caused by the dim light, but even if there was, it would be very slight – at worst, less than the level of short-sightedness where you would start to need glasses.

So if dusk's approaching and you can't put that book down, there's no need for alarm. But you'll be a lot more comfortable if you turn on a light.

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Sources and Additional Information:

2 comments:

Anonymous said...

does reading in dim light damage your eyesight? please tell me i need it for homework thanks by Nisha

Michael Pekker (AKA Nesher) said...

Hi Nisha,
Preparing this post, I've done some research. There is no evidence that reading in dim ligh harms your eyes, however there are getting tired faster than with normal light.

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