That crust is a type of rheum, a thin mucus naturally discharged from our eyes, noses and mouths. Rheum is made up of mucus, skin cells, oils and dust. The rheum that comes from the eyes and forms eye boogers is called gound, which you may know as eye sand, eye gunk, sleep dust, sleep sand, sleep in your eyes, or eye shnooters. When you're awake, gound doesn't cause any problems. You don't even know it's there because it gets cleaned away whenever you blink. Your eyelids regularly corral it down to your tear ducts, where it's washed away. When you sleep, though, you're not blinking, and gound is allowed to build up in the corners of your eyes. It dries out and hardens, leaving you looking like you face planted in a sandcastle sometime during the night. Gound isn't a big deal for most people, but an unlucky few have a major problem with it. A number of conditions, from overactive oil glands to blocked tear ducts, can lead to obscene amounts of gound buildup, sometimes to the point where it prevents people from opening their eyes.
