I'm guessing that a 40" tv is going to be lousy quality as a monitor.

Better would be to:-

* Get an eye test, and wear suitable glasses * Get a GOOD monitor * Use a good font; use a large font * Use suitable lighting * Take regular breaks * Fix a mirror behind the monitor, so that you can allow your eyes to change focus every now and then.

I used to work 55 minutes, take a 5 minute break, on top of my legal minimum breaks. (I'm in England.) Obviously, I'm not a doctor.