Why Do My Eyes Water?


– Have you ever had your
eyes water sometime? You’re not feeling
emotional, you’re not crying, yet there’s just tears running down. What is that all about? That’s what we’re gonna talk about today. (old rock music) You’ve probably heard that
the eye is like a camera and that is accurate. The one difference, well
there’s lots of differences, but one of the differences between the eye and a camera is that a camera
has to have a perfectly clean, totally untouched surface to the lens. There can’t be any dust on there and there certainly can’t
be any water on there. That’s the complete
opposite of how the lens on the front of your eye works. That lens is called the cornea and that corneal dome is this clear window that we look through. It’s also a lens ’cause
it’s got a curve to it. But if there’s any area of the cornea that doesn’t have water
just coating the surface. If it’s not perfectly varnished with this nice, clear film of tears, then we start to have blurry vision. So our eye has a mechanism
built in to help with that. It’s called, it’s called baseline tearing and baseline tearing is just the tears that you produce all the time. You’re not thinking about it. You don’t have to because your body’s autonomic nervous system takes care of it. There’s a natural secretion
of tears all the time. Now, if we drew out an eyeball with the lids and everything, it would look a little bit like that. Now when we’re talking
about baseline tearing, what we’re talking about is just underneath the lid there’s all these tiny little, tiny little openings. There are these little glands called the glands of Wolfring, named after a guy named Wolfring, and the glands of Krouse, and those guys had discovered
all these tiny little openings where you just secrete this
constant little flow of tears. You have them in your lower lid as well. They’re all along here down here. And there’s millions
and millions of these, and so all together they can secrete just this
normal amount of tears. And it just always coats
the surface of your eye. So if you were to look
at an eye from the side, it would look like this, and the cornea is this dome on the top, and the only way that that dome can stay wetted all the time is by having lids that are
always blinking that across. Now to illustrate the
point of what happens when we have eyes watering, I’m going to end up making this flat because it makes it easier to draw. But the miracle isn’t that
sometimes our eyes do water. It’s that they’re not
watering all the time because if you think about it, you have this constant
production of tears, but what’s to keep that from overflowing? Well, there’s two things. And those two things are
good old evaporation. If you spill a cup of water on the ground, you come back the next day, all the water’s gone. It’s just evaporation that took it away. And the other one is
the nasolacrimal duct. You have these little openings. And there’s these little canals. They’re called a canalicula’s
here and a canalicula’s here and they just carry tears away, and they go down into your nose. That’s actually why you get the sniffles if you cry a whole lot because your canals are overloaded and dumping all those
tears into your nose. You’re actually sniffling tears. But between those two things the drainage through
this nasolacrimal system and also from evaporation, you have this normal amount
of tears in your eye, and it’s not too much. But what if it’s too little? And that’s what happens when
we have the second problem. Which is watering eyes, and that is because of reflex tearing. So, I said earlier I was
going to make this flat. So if we pretend the cornea
is this flat surface. What we want to have is this nice little lake
of tears all the time. Just for clarification, there’s
not actually waves there. That’s just so it looks more like water. But what happens if we
get these dry spots? It looks more like this. There might be a little bit of water here. A little puddle here, but
there’s a dry spot right here and then there’s another
little bit of water here and then there’s a puddle here, and so when we have these dry
spots on the font of the eye, our eye can sense that. We don’t know it’s there, but our eye knows it’s there because you have this nervous system it’s full time job when
it comes to your eyes is to make sure there’s
always gotta be enough tears. And so when that happens and
you form these little dry spots you get reflex tearing, and it doesn’t come from
these tiny little glands. It comes from this big, big gland up here. And it’s called the lacrimal gland because lacrima is tear in Latin or the Lacrimosa like Mozart
wrote, and that’s crying. That’s tears, the lacrimal gland. And it’s job and it’s big too. I mean, even if you’re
talking about eye stuff we always talk about things
in really small terms, but the lacrimal gland
it’s the size of a grape. It’s big. And so it dumps a ton of
tears and it floods over what it’s supposed to do big flood over all this stuff. And then all of those
islands are underwater again and you’re okay as far as the surface of
your eye is concerned. But there’s too many of them. Evaporation and the nasolacrimal system, they’re not enough to keep up with that, and so all of a sudden your
eyes start running water. It’s the reason that if you have ever had that car air vent
just blow on your eye for a little while, all it
takes is a little bit of time and tears start pouring down your face. It’s because you’ve created
these little dry spots, and in an effort to rescue
the front of your eye, your lacrimal gland has come in and said, I’ve got this and sends
a reflex rush of tears down the front of your eye. And some of them go over your lid and down your face and make
you look like you cried. And that’s why our eyes water sometimes.

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