This is not a matter whether you use a tv as a computer monitor or just using real computer monitor. If you spend many time on looking the monitor without rest, it is bad for eyes. It look at the monitor for a long time, it will cause eye strain, dry eyes and tired eyes. If you often strain your eyes, you can even cause some vision problems such as myopia.
The effect the TV gives is just as same as the computer screen. You should not stare at it for a long time. Or else, your eyes may get tired easily. The big screen will shoot into the eyeballs directly which may shrink the reflection of the normal procedure which may cause the short sighted eyes if seeing for a lot of time.
Well, it all depends on several factors to be honest. Actually, in the past, TV set will give out a lot of harmful lights and radiation which would definitely harm your eyes to a large extent. However, with the development of technology, current TV sets are much more healthier than those in the past. Also, the distance between you and the TV set plays an important role. Meantime, you should know whether the TV is suitable for computer use. If the answers are satisfactory, you are ok to do so. Good luck.
Oh, dear child, I have to say, use the TV as a monitor of a computer screen, it will be wrong for your eyes to use it as a computer. You know the displayer will be more clear and exquisite than the TV. TV only suitable for the long distance watching while displayer suit to watch in a near distance. Computer must be high resolution and mild colored, that is better to your eyes. The substitute will be deficient for your health of eyes.