Fibrous Layer of the Eyeball - Video Tutorials & Practice Problems

Fibrous Layer

As we look at the layers of the eye in a little bit more detail, we're gonna talk about the fibrous layer first and the fibrous layer is going to be the outer most layer of the eye. And we said that is there really to protect the eye. We said to give it shape and also to be an attachment site for muscles, right? So as you look around, it's because you have muscles attached to this fibrous layer, pulling that eyeball back and forth. Now, it's called the fibrous layer because it's made of fibrous connective tissue and the fiber we're talking about here, Collagen. So remember collagen is strong, like a rope really hard to break, but it's also very flexible. So that's what makes up this fibrous layer. So the outer layer of your eye is really tough, but it's flexible, your eye can squish a little bit. All right. Next, we're gonna look at our image here and I just wanna orient you to this image because we're gonna be using this image over and over again. For our different layers, we're just gonna highlight it differently for each one here we are looking at a transverse section of the eye. So this is a top down view of the eye. And specifically, we are looking at the right eye. So we can see here in blue all the way around the outside, we have this fibrous layer, but you'll see that we have color coded a light blue and a dark blue in light blue. Here, we have the cornea and all around the back in the darker blue, we have the sclera. All right. So let's start with the cornea. The cornea you can see there is the front section and it is transparent and it's transparent because you gotta look through it, right? And so we said we're gonna talk about these layers in the order that light hits them. So as your in light interacts with the eye, the first thing it needs to do is it needs to pass through this cornea to enter the eyeball. So we're gonna say that the cornea allows light to enter and it also is going to protect the eye. The cornea is going to be highly innervated and it's gonna be innervated mostly with pain receptors. So while it is really tough, it's a really tough material, it doesn't feel really tough. And we've all had the experience right, getting a grain of sand or even just an eyelash in your eye, you know how darn uncomfortable that is. And that makes sense because you want a really nice clear thing to look through, you don't want it to get all scratched up. So when anything gets on that cornea, even something as simple, an eyelash that you wouldn't feel anywhere else on your body, it's deeply uncomfortable because you're gonna spend a lot of time very gently trying to remove it. All right, the cornea we are going to say is going to be continuous with the sclera and by continuous, we just mean that those fibers just run into from one to the other. Now, interestingly though, and you probably don't need to know this, but I find it very interesting that the cornea actually develops from a different em embryological tissue than the sclera does. They develop from different tissues in the embryo, they grow together early on in the eye and then become this continuous fibrous outer layer. All right. The last thing you need to know about the cornea here is that it is a vascular, there's no blood vessels in your cornea because you gotta look through it. You don't wanna be looking through blood when you're seeing things. Ok, we'll now move to the rest of this fibrous layer and that is going to be the sclera. The sclera is most of the outside of your eye, roughly 80% of the surface of your eye. We're gonna say that it's really just the white of your eye is what you probably refer to it as and it is there to protect the eye. And also it gives the eye its shape, right. So the eye is this collagen, this fibrous material. So you really want to think of it almost like a soccer ball. It's really tough. It has shape to it, but to keep that shape, it needs to be inflated and it's gonna be inflated with that aqueous humor and the vitreous humor. And we'll talk about that in more detail coming up later. All right, here though, we're gonna say that the sclera protects and shapes the eye and it also anchors the eye muscles. So we've been saying that the eye muscles attached to the fibrous layer, specifically, they attach to the SCLE, ok, like the cornea, the sclera is innervated, but it is less sensitive, right? And that makes sense. It's not quite as big a deal if you get a scratch on your sclera. So things on your sclera are uncomfortable but not quite as uncomfortable as if you get it right on the cornea. Now, the sclera, we said the cornea is continuous with the sclera, the sclera is gonna be continuous with the dura mater of the CNS. And if you remember from the central nervous system, the dura mater, that is that our outer layer of the meninges, this really tough membrane that surrounds the brain and the spinal cord. In fact, dura mater literally means the tough mother. So this uh the sclera actually surrounds the eye and then it just comes back and it surrounds the optic nerve and goes back and is continuous with that membrane that surrounds the brain. Now, interestingly again, you probably don't need to know this. But the eyeball develop mentally, actually develops, most of it develops as an outgrowth of that central nervous system. So it's almost like the eye is like a pimple of the brain. Someone once described it to me as which I kind of like. And you can think of that, that, that makes sense because it has this continuous layer with that dura moderate that's surrounding the rest of the central nervous system. All right, the last thing that we need to know here is that the sclera contains blood vessels and if you've ever gotten bloodshot eyes, you know that's true. OK. So that's the fibrous layer, the outer layer. Next, we'll talk about the middle layer or the vascular layer. But before we get there, we got example and practice problems. Give them a try.

Fibrous Layer of the Eyeball Example 1

All right. Here, we have a few questions about the fibrous layer of the eye. It says what material is the fibrous layer of the eye mostly comprised of? We want to name at least one other body structure that is mostly comprised of the same material. And then we, it says based on what you know about the material and other structures made of that material, what properties would you expect of the fiber slayer? All right. So remember the fibrous layer that's shown here in blue on this cross section of the eye, we have the sclera making up the white of the eye, most of the back of the eye and then the cornea in the front there. So what material did we say that the fibrous layer is made of? Well, like its name, we said the fibrous layer is made up of fibrous connective tissue and we said fibrous connective tissue, that's mostly collagen. I'll just put that in parentheses here. All right. So, fibrous connective tissues, mostly collagen. Well, where else in this course so far have we talked about fibrous connective tissue or places with a lot of collagen? Well, when I think about that. I think about tendons and ligaments, tendons being the link between muscles and bones and ligaments. The connection between two bones, those are made of fibrous, connective tissue and a lot of collagen. But we've seen connective tissue with collagen in other places as well. You can remember that the matrix of bone, the osa the organic part is mostly collagen. It gives the bone that strength. But when I think of those tendons and ligaments, specifically, what properties do they have that? I think that I will also share well, collagen, what properties have we talked about? Collagen, having collagen, we said is really strong, like a rope, you can pull on it, yank on it, it's really hard to break, but also like a rope, it's flexible, it's really easy to bend. So I would expect this outer layer of this eye to have those properties. So I'm gonna write strong and flexible and I sort of described and I think it really helps to think of the eye kind of like an inflated soccer ball, right? That soccer ball is really tough. It doesn't pop easily, but it's not hard, right? You can squish it. And the same is gonna be true for the eye. Now, I don't suggest you try to squish your eye. But if you had an eye and you squeezed on it, it will squish a little bit, but also like a soccer ball. If it gets stabbed, that sucker is gonna pop and you really don't want that to happen. So take care of your eyes.

Which of the following statements is true of both the cornea and the sclera?

• A. Both the cornea and the sclera are innervated.
• B. Both the cornea and the sclera are avascular.
• C. Both the cornea and the sclera anchor muscles that move the eye.
• D. Both the cornea and the sclera are transparent to allow light to enter the eye.