Eye discharge, or “sleep” in your eyes, is a combination of mucus, oil, skin cells and other debris that accumulates in the corner of your eye while you sleep. It can be wet and sticky or dry and crusty, depending on how much of the liquid in the discharge has evaporated.
Other slang terms used to describe eye discharge include eye boogers, eye mattering, eye gunk, eye pus and goopy eyes.
Sometimes called rheum, eye discharge has a protective function, removing waste products and potentially harmful debris from the tear film and the front surface of your eyes.
Your eyes produce mucus throughout the day, but a continuous thin film of tears bathes your eyes when you blink, flushing out the rheum before it hardens in your eyes.
When you’re asleep — and not blinking — eye discharge collects and crusts in the corners of your eyes and sometimes along the lash line, hence the term “sleep in your eyes.”
Some sleep in your eyes upon waking is normal, but excessive eye discharge, especially if it’s green or yellow in color and accompanied by blurry vision, light sensitivity or eye pain, can indicate a serious eye infection or eye disease and should be promptly examined by your eye doctor. (Click here to find an eye doctor now if you don’t have one.)
About: Where Does Eye Mucus Come From?
Eye discharge is a function of your tear film and a necessary component of good eye health. Eye rheum primarily consists of thin, watery mucus produced by the conjunctiva (called mucin), and meibum — an oily substance secreted by the meibomian glands
which helps keep your eyes lubricated between blinks.
When not washed away by tears, the accumulated debris, or “mattering,” collects in the inner corner of the eye as well as along the lash line…..
Source: All About Vision