Rheum is a medical term for the natural mucus discharge from the eyes, commonly known as matter, sleepydust, sleepers, sleepies, sleepy men, sleepy seeds, eye boogers, eye gunk, eye goopy, gound, or legaña. The discharge forms a crust on the eyelids, or gathers in the corner of the eye during sleep (contrast to mucopurulent discharge). It is formed by a combination of mucus consisting of mucin discharged from the cornea or conjunctiva, tears, blood cells, skin cells from the eyelids, and dust.
https://en.wikipedia.org/wiki/Rheum
People have given that “stuff” we get out of our eyes in the morning many different names. Some call it “matter”; others call it “sleep,” “sleepy,” “crusties,” or “eye boogers.” But whatever it is called, there is no denying that we all have it and would like to know what it is.
One of those organs was the plica (PLY-ka) semilunaris (sem-ee-LOO-ner-is), which is located around the eye. For many years, this organ was thought to have no function. But lo and behold, eventually it was discovered that this “useless” organ has an important function after all.
In fact, it is the “crusty” factory. It secretes a sticky mass that collects any foreign materials such as dust or pollen. All this trash is surrounded by the sticky gook so that it does not scratch the sensitive cornea in your eye. Once the garbage is collected, the plica semilunaris “escorts” it out of the eye just like a security guard would escort noisy troublemakers out of a theater.
https://healthmagazine.ca/health/what-is-the-reason-for-the-pink-part-in-the-corner-of-the-eye-plica-semilunaris/
https://en.wikipedia.org/wiki/Plica_semilunaris_of_the_conjunctiva
