I use to use my 42 in as a monitor on my desk but my desk was like 4 feet deep and i was always sitting back like 6 feet away from it. But since its a nice 120 hz tv it wont be as bad but as ksham said. ANY TV will case eye damage with time. I would think having a bigger screen means bigger icons and your not straining your eyes to seem small print all the time so it may be easier on the eyes at times.
How big is the TV? I would say if its 40 inches or less it would be ok. Anything bigger than that at 3 feet is WAY too big.