Rheum

[1][2][3] Rheum dries and gathers as a crust in the corners of the eyes or the mouth, on the eyelids, or under the nose.

Dried rheum near the eyes is commonly called 'sleep',[4] ‘sleet’, 'sleepy-seeds',[5] 'sleepy buds',[5] 'sleepy bugs', 'sleepy sand',[6] 'sleepy winks', 'eye boogers',[6] 'eye goop',[6] 'sleepy dust',[6] 'sleepies',[7] 'eye gunk',[7] 'eye crust', 'sleepy men', 'crusties', 'dozy dust', 'eye globs', or 'sleepy dirt'.

[8] When the individual is awake, blinking of the eyelid causes rheum to be washed away with tears via the nasolacrimal duct.

The absence of this action during sleep, however, results in a small amount of dry rheum accumulating in corners of the eye.

The presence of pus in an instance of heavy rheum buildup can indicate dry eye or conjunctivitis, among other infections.