Since your eyes get blurry after reading in a period of time, it is just a sign to remind you get a rest. From this point, it is normal. Just take off your eyeglasses, and close your eyes for a rest. Or you can look some green plant that can help release tired eyes. It is believed that people shall take a break every hour when they read something so as to keep eye health. If you still get blurry vision after rest,you'd better visit an ophthalmologist.