Excerpt from terminology in Dune:
Ibad, eyes of: characteristic effect of a diet high in melange wherein the sclerae (whites) and irises of the eyes turn a deep blue (indicative of deep melange addiction).
First described in Dune:
The Baron stared across the room at his Mentat assassin, seeing the feature about him that most people noticed first: the eyes, the shaded slits of blue within blue, the eyes without any white in them at all.
First named in Dune:
"My duty is the strength of the tribe," Stilgar said. "That is my only duty. I need no one to remind me of it. This child-man interests me. He is full-fleshed. He has lived on much water. He has lived away from the father sun. He has not the eyes of the Ibad. Yet he does not speak or act like a weakling of the pans. Nor did his father. How can this be?"