Has anyone experienced any eye sight problems on the iPad 2? I recently got a 2012 iPad 2 and loved everything about it except the irritating eye pain that would inevitably occur from using it for more than 10 minutes. Now I'm using an iPad 4, and while the screen is much easier to look at.... It is awfully heavy. I am considering an iPad Mini, but I'm a bit afraid of the eye strain horror stories. Could somebody who has used all 3 chime in and give me any feedback as to which iPad is the least problematic of the three?