Well, generally speaking, it is normal to have blurry vision, if you look at iphone screen for a long time. First, you should know that if you look at iphone screen for a long time, it will just make your eyes focus on the small point too long. And then that can just make your eyes be stressed, leading to eye strain. There are long term effects of eye strains. For example, it can put stress on the eye muscles and the facial and scalp muscles, causing pain and headache. And what is worse, it can lead to making your vision become worse, leading to blurry eyes.