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Is there any evidence that watching television for too long or while sitting too close weakens the eyes (leading to myopia, for example) ?

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My grandma even said that it would cause your pupils to become rectangular :) –  Lagerbaer May 6 '11 at 5:32
    
Anecdotal Evidence: Yes, my eyes are terrible and I've spent a good chunk of my life staring at a monitor. On the other hand, the rest of my family wear glasses anyway, so maybe the two are unrelated! –  Phoshi May 25 '11 at 20:10
    
@Lagerbaer: Your grandma is cool. –  Randolf Richardson Jul 11 '11 at 8:48
    
Getting "square eyes" from too much television is a common expression. –  Oddthinking Jul 25 '11 at 5:59
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3 Answers

There are two theories about this myth which I've heard:

  1. Watching TV causes eye strain, eye strain damages the eyes
  2. The TV set emits "cathode rays" which damage the eye directly

Let's debunk them in order

Eye strain theory

It's a well known fact that watching TV causes strain (tiredness) in the eyes. Any ergonomics source will tell you that. The problem here is that eye strain causes are many - TV, computer, books, driving, etc.
Another problem is that if you are short sighted and your sight is uncorrected (typical case would be a child with uncorrected eyesight), then the strain gets worse. This leads to confirmation bias (i.e. "My son had eye strain and then was diagnosed with myopia, therefore eye strain causes myopia" whereas the the causal relation is the opposite).

So, yes, TV can cause eye strain, as many different other things - this partially debunks the myth because TVs don't have any particular status here.

Does eye strain cause myopia? No. Eye strain might precipitate the onset in some cases, but there are no ways to prevent myopia. Furthermore, it's quite certain that myopia is of genetic origin. See the following references: 1, 2, 3, 4

So we can see that the eye strain theory does not stand on its feet.

Cathode rays theory

This is easily debunked. Yes, old school CR tubes did use beams of electrons to generate images. The thing is, these beams are tightly focused on the screen in order to have a focused image. This is obtained through different means, but basically the electrons hit phosphors in the screen which is a wire mesh - conveniently it is also a Faraday cage which prevents them from going anywhere.

The actual image is made of phosphor generated light. It's just light :-)

That said - there is a small amount of X-rays being emitted, but it's tightly regulated to super-low levels and it is widely considered innocuous.

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As for the Cathode Hypothesis (and I'd suggest editing the post to use that wording), most TV's now are LCD (with LED and Plasma), which use different technology altogether. –  Ustice Mar 7 '11 at 14:48
    
Wow, I've always thought CRTs emitted alpha radiation, too. (Not that that is a health concern.) I must have had that misconception for most of my life! Thank you. –  Oddthinking Jul 25 '11 at 6:07
    
@OddThinking Alpha radiation? As in alpha particles? No way, those are like Helium nuclei: two neutrons, two protons. The only way you get alpha particles is from some serious nuclear action: splitting of atoms. –  Kaz Feb 4 '13 at 21:34
    
@Kaz: OOOOPS! I meant beta radiation. i.e. electrons. Sorry for the schoolboy error. Thanks for picking it up. –  Oddthinking Feb 4 '13 at 21:50
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According to the Straight Dope, in ordinary circumstances watching too much TV or sitting too close will only lead to eye fatigue, not eye damage. Some studies claimed that exposure at too young an age can cause myopia, but at the time of writing (1992), there was no definite proof.

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Focusing on anything for an extended period of time can cause eye fatigue. Older eyes tend to recover from the fatigue more slowly, which may lead to some perceived vision loss during the recovery time.

There's no real evidence to suggest focusing on a TV is any worse than anything else.

Link to more or less random page which agrees with me

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Perhaps you meant: "Older eyes tend to recover from the fatigue more slowly" –  luvieere May 25 '11 at 18:19
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@luvieere Yes, I did. –  mootinator May 25 '11 at 18:23
    
That page cites the American Academy of Ophthalmology (AAO). If you could follow that up and cite them directly, your argument would be much more powerful. –  Oddthinking Jul 25 '11 at 6:09
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