Unless I missed something when we were covering eye physiology at uni, contact lens screens are useless. The area we can actually attend to and process data is tiny, which means the screen has to be directly in the center of the contact.

For example: A physically separate screen means you can swivel your eyeball and look at a different bit of text on a book page, or a different character on a movie screen. With a contact lens display the content you are attending to is always on the center and swiveling your eyeball to change targets will do nothing.