It is normal to get strain eyes after a lots of reading. To relieve the eye strain, you shall take a break and have a rest for your eyes. You can close your eyes for a little time to relax it. Then, try to roll and blink your eyes and close your eyes again as tight as possible. Next, try to change your focus, you can look far away through window. Besides, apply some over the counter teardrop product can also help the eyes. At last, you'd better go out to received natural light a few time. Hope these tips can help you releases eye strains.
As far as what I know, eye strain can usually be caused by sitting for too long in front of the computers or some other electronic device. Of course, if you have read a book for a long time, it is also very possible for you to get eye strain. At this time, you need to stop to have an about 15min rest. You can go to the window to look far so that your eyes can get fresh air as well as relaxed. Keep a correct posture when you are sitting. Do not sit strangely just for a comfortable feel, which will definitely harm your vision and sometimes even your body shape.