che brings up another great point. You have to remember that you are staring at a box for an extended period of time. Depending on those settings (resolution, etc.), it may strain your eyes faster than normal.

Also, how close are sitting to your television? The manual for my PS2 says to sit as far away as possible to the TV. My GBA's says at arm's length. And the general rule for most televisions is at least 3 feet or 1 meter (for all you metric people).

There are so many factors that may be causing it.