The topic was raised on the most recent show of the gritty gunk that forms in the corners of a sleeping person's eyes, and listeners were invited to submit their own family terms for it. Since there's no thread yet specifically set up to collect those terms, I'll start it off (knowing full well that others are sending their own entries through Bookster and Twitface and whatnot.
When I was growing up, it was always just called matter. "Hey, kid, wash your face; you still got some matter in your eyes." Made it easy to understand what's probably the most disgusting Beatles lyric ever written, from I Am The Walrus, about "yellow matter custard, dripping from a dead dog's eye".
There are (at least) two other threads: sleepy-bugs and nerd vs geek full episode.
In our family we always called this matter "sleepers" .... Oddly enough we used the same word to name the pajamas we wore when sleeping to manufacture this stuff....