Video: Lacrimal apparatus
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We all have moments like this, where we're crying and crying a bit more and a bit more and then before we know it, we're a complete mess, with our nose running like a faucet. What's going on here? ... Read more
We all have moments like this, where we're crying and crying a bit more and a bit more and then before we know it, we're a complete mess, with our nose running like a faucet. What's going on here? Why, when I already have a river of tears streaming out of my eyes do I need to turn my nose into a waterfall? The answer lies in the lacrimal apparatus, and lucky for you, that's what we're going to talk about in this video.
Before we jump into the anatomy of it all, let's talk about what the lacrimal apparatus actually is. The lacrimal apparatus is a group of structures responsible for generating tears and collecting and draining the tear fluid. The tear fluid is made up of water and contains many electrolytes, proteins, and more. It functions as a lubricant for the eye and protects it from infection.
Now let's get into the anatomy. Here's a quick overview of what we'll be looking at today, and we're going to start with the relevant bones around the lacrimal apparatus to really orientate ourselves with where the components will lay, then we'll get to the lacrimal apparatus itself starting from where the tear fluid is produced. and ending with its drainage point. Let's get to it.
First up are the bones that are involved with our lacrimal apparatus. This is the image that we're going to be looking at most often in this tutorial where we can see the superolateral section of the right eye and the right nose cut in section. We're looking at the lacrimal apparatus on this person's right side. Many superficial structures have been removed, so we can see the deeper components of the lacrimal apparatus. I'll point these out as we go along.
Looking in the superolateral aspect, we can now see a bone highlighted in green. This is part of the frontal bone. The frontal bone has been resected slightly to see the underlying structures. Let's peel off the skin and muscles for a moment and have a look at the bones underneath. The image now on the right shows more of the frontal bone, which is orange in color. The section highlighted in green is the zygomatic process of the frontal bone and corresponds to the resected section on the image on the left. It's tucked behind here that we’ll find the lacrimal gland which we’ll identify shortly.
Moving to the nasal cavity, we can see right into it. The skin and cartilage have been removed as has the nasal bone. What we can see highlighted in green now and in our pop-out is the middle nasal concha. This is a projection of the ethmoid bone into the nasal cavity. This image on the right is of an isolated ethmoid bone. Quite the funky bone, hey?
The middle nasal conchae are highlighted in green, one on either side. The bony projection in the middle is the perpendicular plate of the ethmoid bone, which makes a part of the nasal septum. Therefore, it is in the midline of the skull. The middle nasal conchae are on either side of the nasal cavity, projecting inwards from the lateral walls.
In this new image, we're looking at a midsagittal section of the skull with the nasal septum removed. The nasal cavity is here, and within it, we can see the middle nasal concha highlighted in green.
Inferior to the middle nasal concha is the inferior nasal concha. This is an independent bone, rather than a projection of another. Similar to the middle nasal concha, however, it projects medially into the nasal cavity leaving a space beneath it. Again, switching it up to this midsagittal section, we can see the inferior nasal concha in the nasal cavity inferior to the middle nasal concha that we identified earlier.
The space beneath the inferior nasal concha is called the inferior nasal meatus. This is an important space in the lacrimal apparatus, serving as the end/or drainage point of the system.
Okay, so now that we've identified our bony landmarks, let's get to the lacrimal apparatus itself.
So, as we mentioned, the lacrimal apparatus is a group of structures that aid in the production, movement, and drainage of fluid from the eyeball, usually to make a tear. There are several structures that are involved – the lacrimal gland, the lacrimal caruncle, the lacrimal papilla, the lacrimal canaliculus, the lacrimal sac, and the nasolacrimal duct.
Let's begin by looking at the lacrimal gland. We'll head back up to the superolateral aspect of the image now where we identified the frontal bone. As you can see, the lacrimal gland is an oblong gland, about the size of an almond, that sits deep to the zygomatic process of the frontal bone. The lacrimal gland is what produces tears – the watery fluid full of proteins and other goods. It consists of two parts – the orbital part which is superior close to the bony orbit and the palpebral part which is inferior close to the palpebra or eyelid – and the lacrimal gland is the beginning of the lacrimal system.
In order for the tear fluid to get from the gland to the eye, it travels through passageways called the excretory ducts of the lacrimal gland, which we can now see highlighted in green. There are usually up to twelve ducts, all transporting fluid from the lacrimal gland into the conjunctival sac in the superolateral aspect of the eye. The conjunctival sac is the space between the layers of the conjunctiva that line the eye and the eyelid.
In this sagittal section of the eye and the orbit, we can see the bulbar conjunctiva lining the eye itself and the palpebral conjunctiva lining the inner aspect of the eyelids. The space between is the conjunctival sac. It is the superolateral aspect of this sac that lacrimal fluid drains into from the excretory ducts.
On the medial aspect of the eye, we can see the lacrimal caruncle highlighted in green. This is the pink fleshy part at the medial aspect of your eye and it contains some sebaceous and sweat glands that secrete a whitish liquid. So, you know in the mornings when you have gunk in the corner of your eye, that's your lacrimal caruncle at work.
The lacrimal caruncle sits within the lacrimal lake. This is where tears accumulate when fluid is moved laterally to medially from the lacrimal gland to the medial corner of the eye. Once tears have accumulated in the lake, we have to empty that lake. And how do you think we do that? Well, that process involves structures called the lacrimal papillae, which as you can see, are situated superior and inferior to the lacrimal caruncle.
The lacrimal papilla is the medial part of each palpable margin, or in other words, the eyelid. In the center of each papilla, is an opening called the lacrimal punctum. It is through the lacrimal puncta that tear fluid drains to continue through the lacrimal apparatus to enter into our next structure – the lacrimal canaliculi.
A single lacrimal canaliculus is a small short, tube-like structure that collects lacrimal fluid for drainage. Medial to the right eye in this image, we see the superior and inferior canaliculi highlighted in green. Medially, we can see the two canaliculi join before opening into the next structure, and this structure that the canaliculi open into is called the lacrimal sac. It is the superior portion of this vertically-running tube, and this vertically-running tube is called the nasolacrimal duct.
After lacrimal fluid passes into the lacrimal sac, it travels inferiorly into the nasolacrimal duct until it exits through the opening of the nasolacrimal duct. The opening of the nasolacrimal duct is in a specific anatomical space that we identified earlier. And do you remember what it's called? Yep – the inferior nasal meatus.
Now remember when we were talking about crying and how if you cry loads your nose may start to run? Well, this is precisely why. When we cry, our lacrimal gland produces more tear fluid than normal. Some of this excess fluid will overflow and roll down our cheeks and the rest will still try to drain through the nasolacrimal duct. But because there are so many more than normal, the tears continue running right out of our nostrils. And you can see how all of this comes together by looking at our diagram here.
Fluid begins in the lacrimal gland, enters the conjunctival sac by traveling through the excretory ducts of the lacrimal gland, then passes over the surface of the eyeball when we blink together in the lacrimal lake. It then travels through the lacrimal puncta which is situated in the lacrimal papillae and then passes into the lacrimal canaliculi to enter into the lacrimal sac. This then passes the fluid into the nasolacrimal duct, which opens into the nasal cavity at the inferior nasal meatus.
So, what would happen if this lacrimal drainage system was then blocked? Well, if you ended up with a blocked tear duct, lacrimal fluid won't be able to drain properly. This would result in symptoms including excessive tearing, swelling at the medial portion of the eye where the canaliculi are blocked, irritation, and possible infection. And there are many different causes of a blocked tear duct including congenital blockage, injury, tumor, or even simply age. As we age, the puncta or openings of the canaliculi get narrower. Treatments generally depend on a specific cause and can include antibiotics or dilating the puncta.
And there you have it! You're now an expert on the lacrimal apparatus. Before I let you go, let's have a quick review of what we looked at today.
So, we started by looking at the bones in the area, first identifying the frontal bone which the lacrimal gland sits behind. We then moved on to the nasal cavity and found the middle nasal concha – a bony process of the ethmoid bone. Inferior to that was the inferior nasal concha – a bone all of its own. And the space behind the inferior nasal concha is called the inferior nasal meatus and is where the opening of the nasolacrimal duct is.
We then moved on to the lacrimal apparatus itself starting in the superolateral aspect where lacrimal fluid is created and secreted, and this is the lacrimal gland made of two parts – the orbital and the palpebral parts. To get from the gland to the eye, the fluid must travel through these excretory ducts of the lacrimal gland of which there up to twelve into the superolateral aspect of the conjunctival sac.
Medially, we identified the pink fleshy part of the eye called the lacrimal caruncle in the lacrimal lake. At the medial aspect of each eyelid are the lacrimal papilla. On each lacrimal papilla is an opening into the drainage system called a lacrimal punctum. The lacrimal puncta open up into the lacrimal canaliculi – one superior and one inferior. The canaliculi then join together and drain into the lacrimal sac, which is the superior portion of this vertical tube called the nasolacrimal duct. The opening of the nasolacrimal duct was the last thing that we identified in the inferior nasal meatus. And, finally, we spoke about the blocked tear ducts and the various causes and treatments of it.
And that brings us to the end of this tutorial. I hope you enjoyed it. Thanks for watching and happy studying.