It is a normal phenomenon and you needn't worry about it. You can't focus on objects just because your eyes are fatigued after a long time reading. This phenomenon will disappear after you have a rest. However, you should develop good habits with the eyes and it is necessary to relax your eyes discontinuously. For example, you can look into the distance or walk around for a while after you read about one hour. Excessive use of eyes may cause vision problems.
According to your description, maybe it is because you are tired. As we know that when you have been reading, that means your eyes focused on one point. If it happens in a long time, it will make your eyes feel stressed. We can say it as eye strain. Then after you finished reading and want to look at other things, it will be hard for your eyes to be accustomed to the situation around. At this moment, they can not focus on easily. So you should be careful about it and just control the time of reading. For example, you can have some eye drops so that it can relieve the symptom.
If you don't have a rest during the two hours continuous reading, you will absolutely feel tired in your eyes. The things you see will be in a blurry. That is why your eyes can't focus. If you do this often, your eyes may get short sighted. I suggest you to have a little rest after 40 minutes continuous use of eyes.