Yes, reading on ipad mini screen for a long time with little rest will make your eyes strain for you. You'd better have the rest for the eyes. The radiation from the screen will stimulate your eyes nerves directly. Thus you'd better wear the protected goggles to sit in front of the ipad which will protect your eyes vision.
Well, yes, it is possible to have eye strain if you watch on the ipad mini screen. And according to some researches, it is normal to have some eye problems if you look at ipad screen for a long time. First, you should know that when you look at ipad screen for a long time, it will just make your eyes focus on the small point. And that can just increase eye pressure and then, your eyes will be stressed, leading to eye strain. What is more, it can put stress on the eye muscles and the facial and scalp muscles, causing pain and headache, even red eyes. So just be careful about it, and it can be harmful for your eyes.
One thing for sure, every digital products are bad for eyes if someone use it for too long then do nothing to relax eyes.
No matter how sufficient light Ipad mini offered, you shouldn't reading it for more than one hours without break.
Eye strain occurs when people's eyes are tired and lack of relaxation. Digital products' radiation make the tiredness comes sooner than normal reading.
It doesn't matter to use Ipad mini if you relax your eyes when they need.