Replying to Computer Screens and Eyes

Do any of you guys notice that computer/phone screens mess with your eyes? My eyes/head always feel really weird after looking at my computer for a while. Almost like I'm sort of dizzy. It feels a lot different than looking a book for a while, so I don't think it's just because of focusing at a short distance for an extended period of time. I notice it a lot more now that I'm at college than I did in highschool, since so much of my homework is online. I know that there have been studies linking TV screens to melatonin deficiency in children, but that's about it. Anyone relate/know more about why?