Several people including Ian were exposed to something, early on in the comic. Their eyes changed color and were more sensitive to light. Hence the dark glasses. Other changes, like Ian’s ability to teleport, came later.
Dweller (04 24 2009), mentions feeling Ian’s eyes scanning the world. I would assume that Dehane would also be able to feel Ian scanning to at least some degree.
Spooky!
May be why Ian wears the dark glasses all the time?