Why do we get sleep in our eyes?

It is known that our eyes fill up with gunk as we sleep, but do we know why?

Firstky, gunk ist that what accumulates in the corner of the eyes over the night, also known as sand or eye boogers.

The structure of eyes is really complicated. Closest to the eye is a layer made of mucus. It coats the cornea and attracts water, which allows the dristribution of the second layer. This layer is really important, it keeps our eyes lubricated and washes away potential infections. Finally, there is also an outer layer composed of an oily substance called meibum. 
This meibum is an oily fluid at a normal human body tempature but at just one degree cooler, it becomes a white and waxy solid, the eye gunk.

Large flakes of this solid can form during sleep for a couple of reasons. First, the body cools down a little bit at night, so the meibum turns solid. Second, sleep relaxes the muscular action of the gland ducts and due to this our eyes are coated with more meibum than usual at night.

Now that we know what the gunk is and from where it comes, why our body makes it? In first place it prevents our tears from spilling out of our eyes and dribbling down our cheeks, our daily-life would be really complicated if our eyes were constantly streaming. But meibum is not the only factor that helps prevent our eyes from drying out. Blinking is important too. The act of blinking hydrate our meibomian glands, cause a little bit of extra meibum and helps the oily meibum and water tears mix together to form and emulsion called tear film. If you spend a lot of time without blinking, the emulsion feels apart an the cornea is exposed to air, and that could be really damaging.

In addition, millions of people have "dry eyes", the disorder leads to eye fatigue, red eye, irritation and the sensation that the eyes are heavier than normal. This disorder apperead due to the excessive use of reading, driving, typing or working, which reduce the frequency of our blinks during those activities.

In conclusion, I thing that writing this post I blinked a lot more than usual because of the fear to get dry eyes, and I will also consider how important gunk is before waking up tomorrow and wipe it away.

DICIONARY:

-Flakes: escates

-Coated: recobert

http://www.bbc.com/future/story/20150428-why-do-we-get-sleep-in-our-eyes