The icons that will be displayed are most likely going to be transparent. This means you can focus on them, or focus on what lies before you. It would probably be like looking out a car window while it rains. You can see what's on the other side easily enough, but you can also focus on the stuff right on the screen in front of you. I doubt anyone has obtained eye problems from car windows and rain before, so this should be fine. I'm more worried about idiots who will be completely oblivious to the world around them while using it.