The sandman strikes again
Why does sleep build up in our eyes overnight?
Upon awakening from a night’s sleep, many people groggily wipe away the grit, remnants of the mythical sandman that have accumulated overnight in the inner corners of their eyes.
The sand is often most pronounced in children, so it’s no surprise the term “eye boogers” emerged. Fresh eye goop is yellowish and squishy, but once dried, it hardens and can resist removal by even the most determined finger.
Before it balls into eye grit, the fluid enables and enhances vision. German physician Heinrich Meibom discovered the meibomian glands in the eyelids in the seventeenth century. The glands create meibum, oil that coats the eye.
Just like the mouth and inner nose, the outer layer of the eye works best when wet. A thin layer of tear film, a fluid made of oil, water and mucus, keeps the eye moist. The oily meibum prevents tear film from evaporating between blinks. It also dams tears, preventing a lachrymal waterfall from streaming downward.
Aside from retaining moisture, the meibum shields the eye and helps to focus incoming light onto the lens. If the outside of the eye were dry, it would not be smooth; an eye as gritty as sandpaper would scatter light and make it unfocused on the lens. Dry eye degrades vision, and in extreme cases dry-eyed patients cannot see the big E on the eye chart.
Too little meibum is painful. So is meibum infected with bacteria. Just as meibum helps hold back tears, so do fatty acids. If harmful bacteria break down the fatty acids, they release free fatty acids — basically broken fatty acids that sting the eye. Often, an onslaught of blinking can encourage tears to rinse away the damage. Other remedies include a warm compress draped across the eyelids, which warms the oil and helps it spread across the eye, and a gentle baby shampoo scrub, which washes out the stinging free fatty acids. In some cases, doctors will prescribe an antibiotic to treat the bacterial infection. People who wake with itchy eyelashes stuck together can use a damp, warm washcloth to wipe the gunk from their eyes.
People still get grit in their eyes after sleeping, even if their meibum isn’t infected. During sleep, the eyes close, the eyelids kiss and the meibum gums together; it collects in a pouch usually reserved for tears and flows toward the nose, snowballing into a pill of oily dead skin and dust. When morning comes, the sandman is nowhere to be seen, but the meibomian glands continue to produce their oily elixir, enabling sight for another day.