According to the Canadian Association of Optometrists (CAO), sitting too close to the TV doesn't cause permanent damage to your eyes. Instead, it causes eye strain and fatigue.
Eye strain and fatigue can be a problem because that means your eyes are tired, which translates to blurry vision. The cure is to rest your eyes and vision returns to normal.
Proper Lighting For Watching TV
While sitting too close to the TV can cause eye strain and fatigue, watching TV in the wrong lighting can cause even more unnecessary eye strain. The CAO recommends that you watch TV in a well-lit room in order to prevent this unnecessary fatigue on your eyes.
Lighting in the TV room is very important. Some people like the room bright, others like it dark. The CAO suggest watching TV in a room that has daylight conditions. The thought being that a room too dark or too bright would force the eyes to strain to see the image.
The CAO also recommends that a person shouldn't watch TV with sunglasses on.
Other than removing your shades, one solution to reducing eye strain when watching TV is to back light the TV. Back lighting is when you shine a light behind the TV. The Philips Ambilight TV is probably the most famous of the TVs with back lighting.
Proper Distance To Sit From The TV
One line of thought is that a person can sit closer to a HDTV because our eyes see the wide screen differently than when viewing the old analog TV. Another one is that nothing has changed. You shouldn't sit with your nose touching the screen.
So, how far should you sit from the TV? The CAO recommends that a person watch TV from a distance of five times the width of the TV screen.
I put the CAO's viewing distance recommendation to the test, which measured out to watching a 42" HDTV from 15' away. The 15' feet distance was a bit far. I preferred a 10-12' distance on the 42" HDTV.
So, my advice is to use a little common sense and move away from the TV if your eyes start hurting. Watch TV from a distance where you can comfortably read the text on the screen without squinting.
If you're watching TV and your eyes start to feel fatigued then move your eyes away from the TV. Try to focus them on something far away for a short time. My favorite example of this in action is the CAO's 20-20-20 rule.
The 20-20-20 rule is actually intended for computer viewing but it really can be applied to any situation where eye strain is a problem, like watching TV. According to the CAO, "every 20 minutes take a 20 second break and focus your eyes on something at least 20 feet away."