Well, generally speaking, it is harmful to watch computer in a long time. As we know that when we watch computer screen, our eyes have to focus on one point for a long time, at that moment, it will make your eyes feel stressed. And then have painful feeling. Also, that can also cause pink eyes, or dry eyes. So anyway, you are not supposed to be long time. To protect your eyes, you should also pay attention to the position. It can play an important role in the eyesight. Also, just have right lighting is also essential. Besides, you should probably make your eyes have enough time to rest. Taking some eye exercises can be effective on the tiredness.