Why Do We Wake Up With "Crusties" or "Sleep" in our Eyes?

From Issue: Discovery 1/1/2001

Dear Craig,

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.

Many years ago, some scientists said that evolution was a fact because the human body supposedly contained parts that didn’t do any­ thing. For a long time it was thought that organs such as the tonsils and the appendix were use­ less ”leftovers” of evolution. These parts were called vestigial (ve-STIJ-ee-al) organs. The word “vestigial” means a trace or a mark left by some­ thing, much like a footprint. It was thought that these “useless” organs were marks or “footprints” of evolution.

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.

Let’s all give the plica semilunaris a big hand for doing such a great job of “taking out the trash” in our eyes. And remember, there are no “footprints” of evolution in your body because your body did not evolve—God designed it!


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