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How Do Our Eyes Create Tears?

Teardrop falling from eye.
The lacrimal glands will produce more tears to counter irritants like cigarette smoke.
Anatomy of the human eye.
A blocked tear duct may cause excessive eye tearing.
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  • Written By: Michael Pollick
  • Edited By: Bronwyn Harris
  • Last Modified Date: 25 July 2014
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It would be more accurate to say that our bodies create tears for our eyes. The human eye itself is protected from outside irritants by a tear film, which is actually three layers thick. The outermost lipid layer is oily, which helps the liquid to remain in the eye. The middle aqueous layer is watery, but also contains chemicals that wash away germs and other irritants. The innermost layer of the film is called the mucous layer, and provides a smooth protective coating over the surface of the eye.

The human body produces tears by stimulating two glands situated above each eye, behind the upper eyelids. These lacrimal glands are responsible for excreting lacrimal fluid, the medical term for tears. Lacrimal fluid is very salty, although there is some evidence that the salinity level changes depending on the cause of the fluid's release. When the brain senses a need for tears, the glands excrete the lacrimal fluid into the upper eyelid area. Gravity or capillary action draws this fluid onto the eye's surface, where it either lubricates the eyeball, washes away the irritant, or simply pools at the base of the lower eyelid.

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Ideally, the excess tears collect in an area known as the lacrimal lake, where they will eventually be drawn into a small opening called the lacrimal duct. If the duct becomes overwhelmed or blocked, however, the excess may spill out of the lower eye and down the person's cheek. The lacrimal duct drains into the nasalacrimal duct, where the tears may either drain into the throat or nasal passages.

The production of tears is essentially semi-automatic. The lacrimal glands routinely produce a small amount of liquid in order to keep the eyes lubricated and free of irritants. If a specific irritation, such as the gas from a raw onion or cigarette smoke, reaches the eyes, then the brain can send out a signal for the lacrimal glands to produce more.

A person can also generate tears through the use of strong emotions. Trained actors often have the ability to generate them in a dramatic scene by using sense memory to trigger a genuine emotional response. So-called "crocodile tears" can also be generated voluntarily by channeling a false emotional response for the benefit of others. Hard squinting can also force lacrimal fluid to pool up, creating the illusion of real tears.

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candyquilt
Post 10

@anon86626-- I think that excessive crying can damage the production of tears or the function of the tear duct.

My great-grandmother had one blind eye. My mom always says that it was a result of excessive crying. She had witnessed the death of her sister and apparently cried for months afterward.

There is a condition called chronic dry eye where the body cannot create enough tears for the lubrication of the eye. And this can lead to eyesight damage and I think that's what happened to my great-grandmother.

fBoyle
Post 9

@SarahGen-- One theory is that crying is a survival system. Our eyes can water up for various reasons like a physical irritant or when our eyes need more lubrication. But when we create tears in response to emotion, it's a survival mechanism for protection.

Emotional tears apparently show that there is a problem. This can be a signal to ourselves that there is an issue we need to deal with or it can be a sign to others that we are vulnerable and should be left alone or helped.

If you think about it, it makes a lot of sense.

SarahGen
Post 8

@anon76807-- I would like to know the same. I know we cry when we're sad, upset, angry and even when we're happy. Buy how do we do it?

Why don't animals cry? I'm sure they experience the same emotions we do but we don't see them crying like humans. There has to be more to this than we know.

StarJo
Post 7

I didn't know our eyes had three layers. With oil, water, and mucus covering them, it's no wonder they are well lubricated.

I've never really noticed that tears come from the top part of the eye. Since they leak out of the bottom corner, I always assumed that this was where they originated.

kylee07drg
Post 6

@cloudel – Some people say to hold a burning match in your mouth while chopping the onion, but that's a terrible idea! I know I would burn myself if I did this.

I've read that if you use a sharp knife and chop quickly, you won't release as many irritants. However, there is one method that my grandmother taught me that works even better than this.

You hold a piece of bread in your mouth while dicing the onion. A big portion of it needs to be hanging out, and I think that it absorbs the gases that the onion releases.

I always do this while chopping onions. I haven't had any problems with tearing up since I began using bread.

cloudel
Post 5

My husband caught me crying tears of irritation in the kitchen the other day. I was chopping a red onion, and the fumes were so intense that my eyes were burning, and tears were streaming out of them.

Is there any way to prevent tears from forming while I'm chopping an onion? I really hate to go through all that burning and crying, and I use onions in a lot of things I cook.

I read once that you could do something with a matchstick that would help. I forgot what it was, though.

seag47
Post 4

I wasn't aware of the nasalacrimal duct. This explains why my nose gets so uncontrollably runny when I cry.

The fluid is so watery that it pours right out of my nose like tears pour from my eyes. If I don't have a tissue handy, I'm in trouble.

I hate to cry in public, but it has happened before. I have even been forced to wipe my nose on my sleeve, because I had no tissue with me.

anon248225
Post 3

Why does the brain send the signal to the tear duct? Why not somewhere else?

anon86625
Post 2

Why don't they stop if you cry for hours? Is it possible to cry all the water out of your body?

anon76807
Post 1

but why does a sad thought produce a tear?

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