This is a common problem that happens to these people who love reading or watch something in a long time without any rest. So I think you should have your eyes rest when you are reading. Maybe you can close your eyes, look at some green plants or look far into the distance after half an hour's reading periodically. Besides, you can fill yourself a pair of reading eyeglasses to protect your eyes.
Some useful measures can be taken to avoid eye strain if you follow these steps. You can do some good exercises to relieve strain. When reading books for a long time, you can also go outside to look into the distance. In this way your eyes can be relaxed. Besides, you can buy eyedrops which can improve your eyesight and avoid eye strain.
If people keep using their eyes for a long period, so that causes the eye strain. In other words, the eyes would feel fatigue after continuous see or watch objects, especially reading. Hence, there are a few tips can help you decrease the eye strain. Firstly, it is helpful for you to read under an adequate and soothing light, which can help you focus on the reading for extended periods of time. And you could concentrate on large enough objects when reading. A pillow supports your neck if you are lying in bed or sitting in a chair, to prevent stress of your muscles. Next, you should take a break after a short period frequently to blink your eyes several times. Also you can place a cold towel over your eyes to keep it until the towel becomes warm.