Comprehensive Overview of Eye Anatomy

Hi, I'm Agent Nerds. In this video, we're going to talk about the structure of the eyeball. Alright, so let's go ahead and get started with this because it's important before we start going into all the phototransduction and going into the retina and looking at all the cells layers of the retina and how these optic pathways are even occurring going to the central nervous system. We really need to just get a good idea about the anatomy of the eye, right? So if you guys have watched some of our anatomy videos, we have a model that we actually go through the eye. But this is just going to go to a little bit more detail in a moment. apply some physiology to it, okay? So let's go ahead and get started. So what are we going to try to cover in this video? Let's come over here and let's get our little outline set up. First thing we're going to talk about is the tunics of the eye, okay? Then I want to talk about these things called segments, like anterior segments and posterior segments and what separates them and what's in them. And then after that, we're going to talk about the flow of this substance called aqueous humor. And you know, we might even throw in another thing called the lacrimal flow, okay? We might even talk about the lacrimal flow. And then we'll throw in a tiny little tidbit in there about clinical correlations. Nothing really insane. Alright, so let's go ahead and start about tunics. So there's actually going to be three main tunics of the eye. Three main tunics. What are those three main tunics? Okay. One tunic that we're going to talk about is actually called the fibrous tunic. That's the first one we'll start with. The fibrous tunic. And this is made up of two things. Okay, so the fibrous tunic is made up of two things. One of them. is going to be the sclera. And we'll talk about the sclera. And the other big component is actually going to be the cornea. Okay, and the other one's going to be the cornea. So the fibrous tunic we're going to talk about is actually going to be made up of two things. One is the sclera, and the other one is the cornea. Then after that, we'll talk about what's called the vascular tunic, or the uvea, okay? The vascular tunic. Sometimes they even call it the uvula. All right, we'll talk about that. And this is made up of three different components, right? So this is made up of what's called the choroid, which is a nice dark pigmented membrane that is important for basically preventing the scattering of light by absorbing that because it contains a lot of melanin in that area. Also, it has a lot of blood vessels, so it gives a nice good vascular supply to some of the layers of the retina. Okay? Then there's going to be what's called the iris, and the iris is important for being under control. specifically the pupil hole size, right? And what's called the ciliary body, which is made up of two things. The ciliary body, if you guys know, is made up of two components. One of the components is called the ciliary muscles. So we're just going to call it the ciliaris, right? And the other one is called the ciliary processes, which are the structures that actually make the aqueous humor. And then we'll talk about one more tunic and we're actually going to have another video specifically digging into that into more detail. But then the last one we're going to talk about is actually going to be the sensory tunic. The sensory tunic. And this is basically the retina. Okay, so we'll talk about that one. And they even include into the sensory tunic, we actually throw into this not only the retina, we also throw into this a little bit of the vitreous humor because it's kind of in that area. But it's more of what's called in a segment. We're going to kind of throw it in there a little bit with the sensory tunic. Okay? Alright, so what do we have here? We have the fibrous tunic, which is made up of the sclera and the cornea. Let's start with that first. Where would you find the sclera in here? And what is the sclera made of? Alright, so if you look here, we're going to have this outer part of the eye. And the outer part of the eye is actually made up of this nice... You know there's actually three layers of the sclera? So we actually kind of... I'm not going to go through every single... component of each one but I'm going to say that there is three layers to the sclera. So if we actually have the sclera here, there's actually three layers of the sclera. One is called the episclera, so that's the outermost part of the sclera. It's made of a really nice dense, fibrous connective tissue. Alright? Very rich and dense fibrous irregular connective tissue. Then underneath that you're actually going to have another one. It's called the sclera proper. And the sclera proper is also important because the sclera proper is actually going to be made of a lot of collagen. So a lot of collagen fiber, so it makes it very tough, right? Very, very resilient. And the last one is actually going to be what's called the lamina fusca. And this is basically very pigmented. So it's pigmented, so it actually is going to have a nice color to it. So we have the lamina fusca and then you're going to have the episclerar, the scleropropa, and the lamina fusca, right? So there's three layers to the sclerot, and it's a really, really important layer. And again, it's made of like an opaque connective tissue. clinical correlation is this because sometimes in certain situations like jaundice certain bilirubin types of molecules can accumulate within the sclera and it can actually cause off like a nice little jaundice like color they say right so you can actually see that in sclera and also very very prevalent in people who have what's called Gilbert's disease which is basically they produce too much bilirubin and accumulates there all right anyway that's the sclera then what's the other part we said it was the cornea this big old orange sucker here right So the cornea is also important. So let's write over here the cornea. So the other super super important component here is going to be the cornea. Now the cornea is important because it's actually made up of, you'd never never believe it, it's actually made with five layers. It's five layers. Just to make it really simple there's one, two, three, four, five. There's an epithelial layer and this is actually probably the most important one. So it's a very very thin epithelial layer. So there's an epithelial layer and this is the outermost. So we're actually going from the outer all the way to the inner layer. So this is going from outer to the inner part of the cornea. This is the epithelial layer. And the epithelial layer is actually rich in a lot of what's called nociceptors or pain receptors. So it's also rich in a lot of what's called nociceptors or pain receptors. Why is this important? Because you know whenever you have... Something irritating the cornea. What are you gonna want to do? If there's irritation of the cornea, there's gonna be sending signals to cause you to want to blink, right? So we have pain receptors there to help us to let us know if there's any type of irritation to the cornea. Also, you're gonna have other layers underneath. They're not super super important, but there's what's called the Bowman's membrane. There's three layers of connective tissue. The Bowman's membrane, then after that there's actually what's called the stromal layer. This is a very thick layer. This is made up of some connective tissue here. And there's also going to be another one called the Desmond's membrane. And this is another connective tissue layer here. So you have what's called the epithelial layer, the Bowman's membrane, the stromal layer, the Desmond's membrane. And there's also one more layer called the endothelial layer. Okay? All right. Now, what's interesting about the cornea is that it doesn't really have a lot of blood supply. Okay? It doesn't really have a lot of blood supply, specifically the epithelial layer too. So because of that, that's kind of interesting. That's why whenever you can do corneal transplants, you can actually do a corneal transplant from one person to another without having any of the projection because there is no immune molecules in that vicinity really. Okay. So again, the cornea is made up of five layers, epithelial layer, Bowman's membrane, stromal layer, Desmond's membrane, and the endothelial layer. And this is where a lot of the blood flow is actually coming in through to give supply to some of the other structures. Okay. So I did a little bit of blood supply coming here near the endothelial layer. Okay, to give a little bit of nutrition to the actual layers around this area. Okay? Alright, so that's the cornea. What is important about the cornea? You know the cornea is important for doing what's called, it's helping to actually allow for the light to pass through here. So it allows for the movement of light. So let's say here is actually going to be light. It allows for light to pass through the cornea. So it's very, very good at allowing for light rays to pass through. Okay, so that's one function of the cornea. It allows for light rays to pass through. All right, sweet. So we've gotten a part of the fibrous tunic, which is made up of the sclera and the cornea. Let's move on to the next part. The next part we said is the vascular tunic. And the vascular tunic is made up of what three components? The choroid, the iris, and the ciliary body, which is made up of the ciliary and the ciliary process. Let's talk about that. Okay, so let's start here first with this big old maroon structure right there. Okay, what is that big old maroon structure right here called? This one coming down this way, this one coming down this way. That's called the iris. Okay, so it's called the iris. So if you guys have seen it like looking at it from an anterior view, you can kind of imagine it like this. Let's say here's the pupil, which is the hole between the iris. Like this right here, this is actually the pupil right here. It's a little hole between the iris, right? Around it, you're going to have all of these actual muscles. So this right here that I'm drawing with these lines is supposed to represent the... Iris and that's made up of a lot of muscles, you know, there's two muscles that make up this right here so again, what is this structure here called this structure here is called the Iris and the iris is actually made up of two different muscles. Okay, so one of the muscles is actually gonna be what's called the dilator Pupillae, okay. So one of them is called I think that's actually I put the pupillae. Let's put the pupillae. So the dilator pupillae Another one is going to be what's called the sphincter pupillae. The reason why I'm mentioning this is because the dilator pupillae is underneath. what's called sympathetic nervous system innervation. Whereas the sphincter pupillae is underneath parasympathetic nervous system innervation. So what do I mean here? If the dilator pupillae is activated, it'll cause the actual iris muscle to relax, which will cause what, what will do to the pupil hole. So if you imagine here, let's say that I have the pupil here is expanding. Okay. It's getting bigger. If it's expanding, that means that it's dilating. The muscles are going to be causing that dilation of the pupil. That's the job of the dilator pupillae, okay? But let's say for whatever reason, the parasympathetic nervous system fibers are innervating the sphincter pupillae, and it's causing the actual iris to contract and constrict that pupil hole, and it's acting like a sphincter. That's called the sphincter pupillae, okay? So again, dilator pupillae dilates the pupil. Sphincter pupillae constricts the pupil. Simple as that. And again, it's made up of a nice muscular layer. So it's made up of muscle there, right? The dilator and the sphincter. But you know what else is important? It's also pigmented. So it's also having some pigmentation to it. So it also has pigmentation. It's what basically determines the color of a person's eye. So for example, you might have brown eyes, you might have some hazel eyes, you might have green eyes, or you might have blue, right? And all that's determining these darker colors is just the accumulation of more of this actual pigments. You know when actually we were born, most of us, almost all of us are born with kind of like a slate gray or bluish pigment. Right? And then over time, the actual real pigment of our actual iris comes out. Okay? Alright, sweet. So we got the iris. Then we're going to go into the next one. This big, big structure right here. You see all this part right here? This whole thing right here. All of this big chunk of muscle right there is called the ciliaris. So what is this big chunk of muscle right here? This big chunk of muscle here is called the ciliaris. All this right here. This is called the ciliaris. Okay, so the ciliaris muscle, what is it doing? What happens is, it's actually, I'm going to show you here in a second, it's connected to the lens, all right? So when it contracts, it changes the shape. of the lens. Okay, here's another interesting point here. The ciliaris muscle is under two different types of innervation. It's under parasympathetic nervous system innervation and sympathetic nervous system innervation. We'll talk about this in more detail when we do what's called the pupillary light reflex, which involves the accommodation reflexes too. But the ciliaris muscle is involved in what's called the accommodation. So we can even put that, which is basically this changing in the shape of the lens. So accommodation, right? These accommodation reflexes, which is important for distance vision and close vision. Alright, just to give you a tiny little tidbit, whenever the ciliaris muscle contracts, so here I'll put it like this, parasympathetic nervous system, it actually will cause the ciliaris muscle to contract. When it contracts, you see these little things right here, these little black lines, they look kind of like strings from a guitar. These things right here are called, you can call them two things. You can call them ciliary zonules, so you can call them ciliary zonules, or you can just call them like suspensory ligaments. Suspensory ligaments. Why these are important is because when the ciliary muscle contracts, these, weirdly, these ciliary zonules become very loose. And when they become very loose, what happens is... This lens starts bulging. So it actually starts bulging. And when it bulges, that's for a very, very close vision. So short distance vision. But if the ciliary muscle relaxes, so because of what system? This would be the sympathetic nervous system. The sympathetic nervous system actually relaxes the ciliary muscle. So it relaxes it. If it relaxes it, weirdly, the ciliary zone will become really tight. And when they become really, really tight, It actually causes this lens to flatten and when the lens flattens that's for very far distance vision. So we'll talk about that when we get into the specifically the pupillary light reflex. Okay, just introducing a piece of it now. Alright, cool. Now, what's the other part? So we've got the iris, we got the ciliaris, there's these little cells here. Okay, see these tiny little cells here that's kind of lining right over the ciliaris muscle. So there's some cells right here and there's some cells right here. These little bad boys right there, these are called your ciliary processes. So what are these little structures they're called? They're called your ciliary. processes and they're a tiny little layer of epithelial cells so they're a tiny little layer of epithelial cells epithelial cells some sort of cuboidal epithelial cells right and what they do is they secrete that humor that aqueous humor so they secrete what's called that aqueous humor okay so look what happens here They secrete this humor. So they're going to be making this aqueous humor because there's going to be nearby blood vessels. So they're going to be having blood vessels serving this area. So if you imagine it for just a second, let's say I remove out this part here, and I put a little blood vessel in here. Because there's going to be blood vessels running all in this area. It gives off little connections. It gives off little connections. And what happens is these ciliary processes can take some of the substances from the blood and make this aqueous humor. Now what happens is this aqueous humor. And these cells could be over here too, right? So they could even have some lining this side too. I'm just showing it here. What happens is, let's actually kind of bring this stuff up here. It moves upwards and as this aqueous humor starts moving, it actually comes up through the back of the iris, right? Comes up the back of the iris. And then it moves through this little hole here. What is this hole here called? The pupil. And it moves into this little chamber right here, which we're going to talk about later. And then from here, it can provide some certain types of lubrication to different structures. structures in that area and can pick up metabolic waste and it can drain into this little hole right here. That hole is called the canal of sclim or slim or you can I like to call it the scleral venous sinus because it just sounds weird. Sounds like I'm saying something like I shouldn't be saying right. So again this structure here is called the scleral venous sinus or the canal of sclim. Okay, and so again what happens the ciliary processes are making this aqueous humor moves up through the you know There's actually a chamber here. I'll mention it now. I might as well because I'm already talking about what is this chamber here? There's two chambers here. There's a chamber here and a chamber here this whole thing though If I were to make this whole distance here, let's do this in pink So it's nice and bright here this whole distance here from the cornea all the way to the lens So from the cornea all the way to the lens There is a specific, this whole thing is a segment. What is this segment here called? This segment is called the post, I'm sorry, posterior. This should be anterior segment. Anterior segment. Now, there's two chambers of the anterior segment separated by the iris. This chamber back here is called the posterior chamber. And then this one right here is actually called the anterior chamber. Now truthfully, it's hard to show it in this diagram here, but what happens is this lens is actually much, much closer here. And the ciliary processes, whenever they're secreting this aqueous humor, what happens is the ciliary muscle has to contract to kind of move the shape of the lens a little bit, so that this aqueous humor can move underneath the lens. And then from the posterior chamber it moves into the anterior chamber through the pupil. Then from that it goes into the anterior chamber and moves from the anterior chamber and drains into this area here. This little hole here called the scleral venous sinus or the canal of Schlemm. Okay, just so that we got that. So the flow of vacuous humor is still the processes are secreting this humor. It moves kind of underneath the lens. because the ciliary muscles have to actually control the accommodation reflex to allow for it to move underneath the lens. Then it moves through the pupil hole. It moves from the posterior chamber into the anterior chamber through that pupil hole. And then it drains into the scleral venous sinus. All righty. Sweet deal. Okay. So let's just recap this real quick because we basically covered these parts here. We got one more layer. But again, sclera. It has episclera, sclera proper, and lamina fusca. And if I'm being very specific to kind of go along with this, how I said that the cornea had an outer layer to inner layer, this would be the same thing. So from outer to inner layer, we're moving downward. So the outer layer is the episcalera, then the middle layer is the scleropropa, and then the innermost layer is going to be the lamina fusca. Alright, sweet. Now let's go on to the next part of the uvea or the vascular tunic. One more part here. Alright, so this posterior extension that's coming from the ciliary body, see this posterior extension here? That's moving all here, this maroonish like structure here. This is all called the choroid. It's called the choroid. So what is this structure here called? This structure here is called the choroid. Now the choroid is important because the choroid is actually going to be a very pigmented membrane. So it's a pigmented membrane. Now I'm mentioning that because that has an important physiological function. When light rays, because you know light rays are coming from many, many different directions through here. When the light rays are coming out here and they could be hitting different parts of the retina, this light rays could actually be scattered throughout the ion, which can cause different problems with vision, right? We don't want that. We don't want this actual light to be scattered through all different areas because it could affect the visual field processing. So what happens is the choroid absorbs some of those light rays that are being reflected, okay? So what is this guy doing here? What is this choroid doing? He's basically absorbing of light because that could affect the actual visual pathway and what we see within our visual fields we don't want that also really important I'm gonna do it in red it has a nice sub vascular supply a lot of blood that are running in this area. Okay so it has a nice little vascular supply. Okay so very rich in vascular supply which is going to nourish a lot of different structures including the retina. So it's actually gonna have a nice vascular supply that can give blood supply to the retina. it's going to be a pigmented membrane which can absorb a lot of different light rays to prevent the reflection of that light and the scattering of those light rays. So that we have very, very precise and very, very good visual pathway without any different types of illusions or anything that could come from it. Okay. All right. Sweet. So we covered that now. All right. Now let's move on. Let's get rid of these light rays here. Let's move on to the next part. What's the next part? So we've covered what? We've covered the fibrous tunic. This part's done here. We covered the vascular tunic. That part's done there. Now we're going to cover the sensory tunic. So the sensory tunic, which is actually going to be consisting of the retina, and we said that we wanted to talk about something else here. All right, if you look here, we were going to talk about this vitreous humor. From here, if you look here from the back of the lens, go from the back of the lens, the posterior part of the lens, all the way back to the retina. Okay. So all the way back to the retina. This whole thing makes up another segment. So the anterior segment was from the anterior part of the lens to the cornea. This segment, the posterior segment, is going to be from the posterior part of the lens all the way back to the retina. Now, I talked about, shame on me, I talked about the ciliary zones and suspensory ligaments, but I didn't really talk about the lens. I said that it's important for basically helping to refract light rays and helping to control our distance vision and our short, close vision. But I didn't really talk about it enough. So let me actually just real quickly talk about this. This is actually the lens, right? Now, what's important about the lens? We said it's responsible for refracting light rays. So whenever light is coming in here, it helps to be able to bend the light, right? It helps to be able to allow for the focus those light rays specifically onto the retina. So it's helping to refract these light rays, okay? So that's one of its functions. But the lens is actually made up of different things. If I were to say here we have the lens, there's actually two components of the lens. The lens is actually consisting of what's called crystalline, like protein molecules. They call them crystallines, which are just proteins. And that makes up what's called the lens fibers. So the lens fibers is actually going to be made up of crystalline proteins. And then you have another component, which is called the lens epithelium. Epithelium. And this is actually going to be consisting of some like cuboidal epithelial tissue cells. So it's actually going to have a little bit of cuboidal cells. Okay. So it's called cuboidal cells. So this is important to understand that the lens is actually made up of two things. What is the lens made up of? It's made up of lens fibers and lens epithelium. Okay, two components here. The reason I'm mentioning this with this whole lens fibers and the crystalline proteins is because in certain situations there is a, you've probably heard of it, called cataracts. They're called cataracts. And cataracts are basically just accumulation or clumps of these crystalline proteins. You know, cataracts can be due to many things. One of the common causes is diabetes. So, in people who have diabetes, this could actually be a cause. Smoking actually accelerates this process. And what else? It could even be congenital. So sometimes just congenital. You know another weird one? It doesn't make any sense, but it could be due to if you consume too much vitamin C. So if you take too much vitamin C, like through supplementation, I actually take vitamin C, that's why it's weird. If you actually take too much vitamin C, this could actually accelerate the... Process of cataracts too. So it's an unfortunate thing here, right? So that's why I'm mentioning the lens because there is certain clinical correlations that whenever there's accumulation of these crystalline proteins, it can cause cataracts, which can definitely make a huge difference in your vision because what is it responsible for? helping to refract some of those light rays onto the retina, to focus those light rays onto the retina, to help with our distance vision and our close-up vision. Okay? And you can actually do surges to replace the actual lens nowadays. So that's pretty cool. Alright, so we covered the lens. Now let's get back to the posterior segment. Sorry for being off track there. Okay, now in the posterior segment it's gonna be made up of all of this pink stuff. Now what's interesting about this pink stuff here is that you make it during embryonic development and you never make any more of it for the rest of your life. Whatever you have, that's what you got forever. So what is this jelly-like material here called? Which it has some types of proteins also within it. as well as other different types of molecule like hyaluronic acid and stuff like that. What is this substance here called? This whole substance pretty much occupying the entire posterior segment is called the vitreous humor. So pretty much this whole posterior segment is occupied by the structure called the vitreous humor. There's actually a remnant like structure that can actually run through here called the hyaloid canal. We're not going to mention it, but it can actually run right within the vitreous humor. We're not going to talk too much about it. Just saying that there is another structure that can run in it, the posterior segment, which is called the hyaloid canal. But primarily, it's going to be made up of this vitreous humor. Now. What's the function of this vitreous humor? What does it do? Well, the vitreous humor is really good at being able to transmit the light rays. So it's good at transmitting the light rays. So any light rays that are coming in here, this vitreous humor is very, very, very good at being able to allow for the light rays to move through that jelly-like material and onto the retina. Also... It's very kind of like a strong jelly-like material. So it actually, you see how right here we have this like black lining here? This black lining here with all this like baby blue underneath it, all this part here, the black line, all the way back to that brown line there, this is going to be made up of the neural layer of the retina. So we'll talk about these two things. There's two parts of the retina, the inner neural layer of the retina and the outer pigmented layer of the retina. What this actual vitreous humor does is it holds the retina. together so it holds the retina the neural layer and the pigmented layer close to one another okay so it holds the neural layer and the pigmented layer close to one another that's another function so it holds retina in place and notice another thing that we didn't really talk too much about what we talked about in other videos you know what's actually connecting over here on the eye like for example let's say that I have a muscle right here the inferior rectus. Let's say that I have a muscle back here, up here I mean, superior rectus. And then you have other ones, medial rectus, lateral rectus, all those different muscles, right? What are they doing? They're called extraocular eye muscles and they're changing, you know, they're moving the eyes. Whenever these extraocular muscles are contracting and pulling on the eyes, they can change the intraocular pressure. But you know what the vitreous humor is very, very good at doing? It's helping to maintain, it's contributing to the intraocular pressure to prevent any excessive. Changes in the intraocular pressure that is occurring whenever these extraocular muscles are contracting. So again, one more time. When the extraocular muscles are contracting, the vitreous humor helps to be able to maintain the actual intraocular pressure. That's its function. When the extrinsic ocular muscles are contracting, it helps to maintain the intraocular pressure. So we can say it contributes to, I'm going to put intraocular. pressure, IOP. Okay, so it contributes to intraocular pressure. Sweet. Now we get on to the freaking good stuff, the meat and potatoes. All right, so let's talk about this one right here. We're going to actually zoom in on it later when we go through the layers of the retina, but I'm just going to take a tiny little piece out for just a second here. So let me pretend that I'm doing this for a second. I'm taking a slice of this, a little chunk of this right here, and I'm going to zoom in on it. Okay, I'm going to take a little chunk of that and I'm going to zoom in on it. Let's come over here for just a second. Alright, so let's say right here, let's say that this is that actual part there, and that was kind of separating, what would this structure be right here? This would be where the vitreous humor is. So let's say this is where the vitreous humor is. Okay, that's all vitreous humor. Then there was the part of the retina that we had here in blue. All this part here. What is this made up of? What is the retina made up of? We'll go over its cell layers in more detail, but I'm going to give you a brief little discussion in it. Very, very brief. This is the outer pigmented layer of the retina. There's two parts of the retina. Okay. What is this blue layer here called? This blue layer is the inner neural layer of the retina. The neural. layer of retina. This is made up of three different types of cells. Well, there's actually more. We'll discuss these in more detail like I said, but there's gonna be what's called photoreceptors. Photoreceptors and these are like your rods and your cones. There's gonna be what's called bipolar cells or bipolar neurons. There's gonna be what's called ganglion cells and then there's gonna be what's called amacrine. and horizontal cells which are basically helping to modify the visual pathway. So a lot of different cells within this area that are making up this neural layer of the retina. Photoreceptors which are consisting of rods and cones, bipolar neurons, ganglion cells, and amacrine and horizontal cells. This is important because we talk about photo transduction we'll see this flow. Okay, so that's make up in the neural layer of the retina. The next one that we said this brown layer is the outer pigmented layer of the retina. So this is the outer pigmented layer of retina. And this is actually made up of these actual epithelial cells. These epithelial cells, so it's actually made up of epithelial cells, kind of like a single layer of epithelial cells, rich in melanin. Very rich in melanin. And that is important for basically being able to help to contribute to preventing the scattering of light rays. So it absorbs some of that light to prevent the scattering and the actual reflection of these different types of light rays. Another thing, what do we say it runs right around this area? The choroid. So the choroid runs in very, very close proximity to this actual... Outer pigmented layer. Why is that important? Because you see these epithelial cells that are actually rich in melanin. We call them pigmented epithelial cells. These pigmented epithelial cells, they basically act like kind of like the part of the blood brain barrier in a similar way. These cells here, they filter whatever is actually coming out of this choroid vessels and determine what actually goes into the retinal area. Okay, so these cells here that are making up this outer pigmented epithelium, they're very special and the reason why is they're controlling what's leaving the blood from the choroid vessels and coming out here into the neural layer of the retina. The reason I'm mentioning this is because in certain types of severe trauma or shifting of movement, you can actually kind of dissect this layer here, kind of dissect this layer right here. And when you dissect this layer right here, what can happen is... Some of this vitreous humor can actually leak in between these spaces. So some of this vitreous humor can leak in between these spaces. When some of this vitreous humor leaks in between the actual neural layer of the retina and the outer pigmented layer of the retina, that's called a retinal detachment. And if not treated very quickly, it can lead to blindness. Okay? So in certain situations in which there is the separation of the inner neural layer of the retina and the outer pigmented layer of the retina, Vitreous humor can come into that little space and cause retinal detachment. And if not treated quickly, it can lead to blindness. Alright, that's that part. One other thing I want to mention here. Let me actually get rid of this part here. Because I want to mention something else with relation to the eye. I'm going to draw another mini eyeball here real quick. Another mini eyeball. Because I want to talk about these things called your eyelids, your palpebra. So let's see here, I draw another mini eyeball. Here's the actual cornea. Here's the pupil and then here's your optic nerve, right? We're not going to draw everything in there. It's not super important. Affricate, we'll do it real quick. Do this here and then that there. Okay? Now, coming right around this area, you're going to have the lower eyelid. So you're going to have a little area right here called the lower eyelid. Then coming over here, you'll have another one which is going to be the upper eyelids. actually make this one look like that one actually do it like this okay so look you'd have some beautiful eyelashes coming off there and some beautiful eyelashes coming off like that right why am I mentioning this two things one there's a little layer here let's do this one in orange orange There's a little layer here lining right underneath this thing. What do we call this? We call this the palpebra. So this is the inferior palpebra, the lower eyelid. This is the superior palpebra, the upper eyelid. There's a little tissue here that's lining not only the eyelid, but it's giving off a little double-layered membrane here that kind of covers a little bit of the cornea. Okay? So there's a little layer here that's actually covering underneath the palpebra. And then there's a layer that's actually covering onto the bulb of the eye here. A little bit on the bulb of the eye. So again, same thing over here. There would be a little layer here covering the inner surface of the palpabra and then giving off a little layer here that kind of covers a little piece of the cornea, like the bulb of the cornea, right? What is this called? This is called the conjunctiva, right? So this part here, that part there that's actually lining the inner part of the palpabra, that's called the palpabral conjunctiva. Palpabral. Palpa. Broll, conjunctiva, and then this inner one here that's actually lining the little parts of the cornea there, that's called the bulbar conjunctiva. Okay, the bulbar conjunctiva. The reason why I mention that is that certain bacteria or viruses can accumulate in this area. People always joke around and say like, oh dude, I'm going to fart on your pillow and you're going to get pink eye. It's partially kind of true if certain types of bacterial molecules or viral molecules get into that little space there and cause inflammation and infection of that area that can lead to what's called conjunctivitis, pink eye. Right? And that's why it's important to know a little bit about that is that if there's the inflammation of the palpebral conjunctiva and then the bulbar conjunctiva this could lead to what's called pink eye or conjunctivitis. Alright? So don't go farting on people's pillows and stuff, all right? Now, next thing. There's another two more important structures in here. Right in here, if I kind of draw it in black here, there's a little plate. A little plate right here. It's called the tarsal plate. So what is that little thing I'm making like a U? That's called the tarsal plate. This has two functions. One function is there's two muscles that connect to it. One muscle is called the actual. the palpebra muscles right so for example you could have the palpebra muscles if there's one up here that'd be a connection of the levator palpebra superioris also it's also a nice connection for the orbicularis oculi so two different muscles can attach to the tarsal plate right so if i kind of draw it like this over here too say i draw it like this i bring it like this right here right there's a tarsal plate right there and again there you have the levator palpebra superioris attaching and then the orbicularis oculi attaching. Okay, that's one function of the tarsal plate. All right, so there's two muscles that are attaching to the tarsal plate. One could be the orbicularis oculi. And if we were to be really specific, there would be another one that's actually attaching up here called the levator palpebra superioris. Okay, so this one up here would be the Levator palpebrae. I'm not going to write all at levator. Palpebrae superioris. Alright, that's one function of the tarsal plates. Another function, there's these actual glands in here called the tarsal glands. So there's glands kind of like inside of that tarsal plate there called the tarsal glands. What happens is these are basically like sebaceous glands and they produce kind of like oily secretions on the eyelid to keep the eyelid and some of the structures on the eye nice and moist and prevent basically the eyelids from sticking together or sticking to the eye okay or the cornea in this case so there's little tarsal glands inside of the tarsal plate that producing sebum and oily secretion to basically keep the palpebra nice and lubricated prevent them from sticking together and prevent it from sticking to like the corneal area okay all right guys i just wanted to take in a little bit of time and pre-draw this structure here because i want to talk really briefly about the lacrimal flow okay because that's kind of important so Lacrimal flow are basically the production of tears which is what Conor McGregor is going to be doing when he fights Floyd Mayweather on August 26. Alright, anyway what happens here if we look at an anterior view of the eye here's your upper palpebra the superior palpebra here's the inferior palpebra you see this kind of like V like part here that V like part there is actually called the Lateral commissure and this part over here is actually called the medial commissure. But don't get that confused with the space between the superior palpebra and the inferior palpebra. That's actually called the palpebral fissure. Okay so this little V part over here is actually called the lateral commissure. V part over here is the medial commissure and the space between the palpebra is called the palpebral fissure. Now this right here is the eye. I'm just showing an anterior view of the nose like this is the nasal septum. And this is the lateral wall of that nose, and this is the lateral wall of that nose. Okay, that side of that nose. All right? Sweet. So let's go here in a step-by-step process. First thing is the lacrimal glands. If you remember the facial nerve, the facial nerve, cranial nerve 7. Cranial nerve 7 was actually one of the big guys there that was going to innervate this guy. All right? And cause this actual lacrimal gland to start producing lacrimal fluid. And that lacrimal fluid, if you remember, it comes out. and moves across the eyeball. So it moves across the eyeball, nourishing the cornea and basically picking up any types of metabolic waste products. And it starts moving medially towards that medial commissure. There's actually a little fleshy part here. A little fleshy part here actually called the lacrimal caruncle. A little area right there called the lacrimal caruncle, little fleshy part there. What happens is, there's these tiny little holes here. Tiny little holes right there around that medial commissure called the lacrimal puncta. So the first step is that lacrimal glands secrete it. They move medially. Then the third step is they move into this hole here called the lacrimal puncta. Then from there, they move through these tiny little canaliculi called the lacrimal canaliculi. Then from that, they move into this big old sack here called the lacrimal sack. Then the lacrimal sack empties. This stuff through this duct here called the nasolacrimal duct and it goes underneath you see how this is the superior concha, superior nasal concha, middle nasal concha, inferior nasal concha and in between it this is the superior meatus, middle meatus and inferior meatus. The nasolacrimal duct empties in just around the inferior meatus into the nasal cavity. Okay so to recap that what's it all doing here first one lacrimal gland secretes. Okay, fluid. Second step, moves across cornea medially. Then third step what? Goes into the lacrimal punta. Moves into lacrimal punta. Then fourth step, goes through these tiny little canaliculi. Then it goes into the lacrimal canaliculi. Then from there it goes into the lacrimal sac. Then from there it goes into the nasal lacrimal duct. And then from there goes into the nasal cavity through the inferior meatus. So I'm going to put inferior meatus of nasal cavity. Holy sweet goodness we did it. Alright. Now, one more thing I want to talk about and then we're gonna go ahead and stop. Alright. There's another little thing that I forgot to mention here, probably one of the more important things here, is that if you're looking here you see this whole big sucker right there? What do you think this is? This right here is called the optic nerve. Okay. This is called the optic nerve. So what is this structure here called? It's called the optic nerve or cranial nerve. This is also called cranial nerve 2. The reason why I'm telling you that is because if we look at the eye, if you do what's called an ophthalmoscope, so you look at the eye from actually doing an ophthalmoscope, you look into their eye, you're going to see in the back of the eye, you're going to see this structure here called the optic disc, that little part there. The optic disc is where the actual optic nerve is piercing through the back of the sclera. Then you'll see kind of a little bit near it, you'll see another structure called the eye. Maculae, right where the fovea centralis is, where the highest concentration of cones are. Okay? But right here is the optic disc. So if I do what's called a fundoscope, you are looking at the back of the eye, there's the optic disc and there's what's called the macula lutea, kind of a little bit more lateral to that. The optic disc is where the actual optic nerve pierces through the back of the sclera. Now when I say it pierces through the black of the sclera, we said, oh wait, I thought the sclera was the episclera, the sclera proper, the lamina fusca. Yeah, it gives a little extension downwards here. And whenever the optic nerve is piercing through the back, it moves these little holes. So the optic nerve, which are the axons of the ganglion cells, they're moving through these holes. What are these holes here in the sclera called? These holes in the sclera are called the lamina cribrosa. Cribrosa, okay? And it's running, it's these little holes within the sclera where the optic nerves are piercing through the back. All right. All right, Ninjas, we covered a lot of information in this video. I really hope you guys enjoyed it. I hope it made sense. If you guys did like it, please hit the like button, comment down in the comment section, and please subscribe. In the next video, we're actually going to take a look more specifically at the retina, zoom in on the retina, all the cells of the retina, and then talk about the phototransduction process. I hope to see you guys there. All right, Ninja Nerds, until next time.

But this is just going to go to a little bit more detail in a moment. apply some physiology to it, okay? So let's go ahead and get started. So what are we going to try to cover in this video? Let's come over here and let's get our little outline set up.

First thing we're going to talk about is the tunics of the eye, okay? Then I want to talk about these things called segments, like anterior segments and posterior segments and what separates them and what's in them. And then after that, we're going to talk about the flow of this substance called aqueous humor.

And you know, we might even throw in another thing called the lacrimal flow, okay? We might even talk about the lacrimal flow. And then we'll throw in a tiny little tidbit in there about clinical correlations.

Nothing really insane. Alright, so let's go ahead and start about tunics. So there's actually going to be three main tunics of the eye. Three main tunics.

What are those three main tunics? Okay. One tunic that we're going to talk about is actually called the fibrous tunic.

That's the first one we'll start with. The fibrous tunic. And this is made up of two things.

Okay, so the fibrous tunic is made up of two things. One of them. is going to be the sclera.

And we'll talk about the sclera. And the other big component is actually going to be the cornea. Okay, and the other one's going to be the cornea.

So the fibrous tunic we're going to talk about is actually going to be made up of two things. One is the sclera, and the other one is the cornea. Then after that, we'll talk about what's called the vascular tunic, or the uvea, okay? The vascular tunic.

Sometimes they even call it the uvula. All right, we'll talk about that. And this is made up of three different components, right? So this is made up of what's called the choroid, which is a nice dark pigmented membrane that is important for basically preventing the scattering of light by absorbing that because it contains a lot of melanin in that area.

Also, it has a lot of blood vessels, so it gives a nice good vascular supply to some of the layers of the retina. Okay? Then there's going to be what's called the iris, and the iris is important for being under control.

specifically the pupil hole size, right? And what's called the ciliary body, which is made up of two things. The ciliary body, if you guys know, is made up of two components. One of the components is called the ciliary muscles. So we're just going to call it the ciliaris, right?

And the other one is called the ciliary processes, which are the structures that actually make the aqueous humor. And then we'll talk about one more tunic and we're actually going to have another video specifically digging into that into more detail. But then the last one we're going to talk about is actually going to be the sensory tunic. The sensory tunic.

And this is basically the retina. Okay, so we'll talk about that one. And they even include into the sensory tunic, we actually throw into this not only the retina, we also throw into this a little bit of the vitreous humor because it's kind of in that area. But it's more of what's called in a segment.

We're going to kind of throw it in there a little bit with the sensory tunic. Okay? Alright, so what do we have here?

We have the fibrous tunic, which is made up of the sclera and the cornea. Let's start with that first. Where would you find the sclera in here? And what is the sclera made of?

Alright, so if you look here, we're going to have this outer part of the eye. And the outer part of the eye is actually made up of this nice... You know there's actually three layers of the sclera?

So we actually kind of... I'm not going to go through every single... component of each one but I'm going to say that there is three layers to the sclera. So if we actually have the sclera here, there's actually three layers of the sclera.

One is called the episclera, so that's the outermost part of the sclera. It's made of a really nice dense, fibrous connective tissue. Alright? Very rich and dense fibrous irregular connective tissue. Then underneath that you're actually going to have another one.

It's called the sclera proper. And the sclera proper is also important because the sclera proper is actually going to be made of a lot of collagen. So a lot of collagen fiber, so it makes it very tough, right?

Very, very resilient. And the last one is actually going to be what's called the lamina fusca. And this is basically very pigmented. So it's pigmented, so it actually is going to have a nice color to it. So we have the lamina fusca and then you're going to have the episclerar, the scleropropa, and the lamina fusca, right?

So there's three layers to the sclerot, and it's a really, really important layer. And again, it's made of like an opaque connective tissue. clinical correlation is this because sometimes in certain situations like jaundice certain bilirubin types of molecules can accumulate within the sclera and it can actually cause off like a nice little jaundice like color they say right so you can actually see that in sclera and also very very prevalent in people who have what's called Gilbert's disease which is basically they produce too much bilirubin and accumulates there all right anyway that's the sclera then what's the other part we said it was the cornea this big old orange sucker here right So the cornea is also important. So let's write over here the cornea. So the other super super important component here is going to be the cornea.

Now the cornea is important because it's actually made up of, you'd never never believe it, it's actually made with five layers. It's five layers. Just to make it really simple there's one, two, three, four, five.

There's an epithelial layer and this is actually probably the most important one. So it's a very very thin epithelial layer. So there's an epithelial layer and this is the outermost.

So we're actually going from the outer all the way to the inner layer. So this is going from outer to the inner part of the cornea. This is the epithelial layer.

And the epithelial layer is actually rich in a lot of what's called nociceptors or pain receptors. So it's also rich in a lot of what's called nociceptors or pain receptors. Why is this important? Because you know whenever you have... Something irritating the cornea.

What are you gonna want to do? If there's irritation of the cornea, there's gonna be sending signals to cause you to want to blink, right? So we have pain receptors there to help us to let us know if there's any type of irritation to the cornea.

Also, you're gonna have other layers underneath. They're not super super important, but there's what's called the Bowman's membrane. There's three layers of connective tissue. The Bowman's membrane, then after that there's actually what's called the stromal layer.

This is a very thick layer. This is made up of some connective tissue here. And there's also going to be another one called the Desmond's membrane.

And this is another connective tissue layer here. So you have what's called the epithelial layer, the Bowman's membrane, the stromal layer, the Desmond's membrane. And there's also one more layer called the endothelial layer.

Okay? All right. Now, what's interesting about the cornea is that it doesn't really have a lot of blood supply.

Okay? It doesn't really have a lot of blood supply, specifically the epithelial layer too. So because of that, that's kind of interesting. That's why whenever you can do corneal transplants, you can actually do a corneal transplant from one person to another without having any of the projection because there is no immune molecules in that vicinity really. Okay.

So again, the cornea is made up of five layers, epithelial layer, Bowman's membrane, stromal layer, Desmond's membrane, and the endothelial layer. And this is where a lot of the blood flow is actually coming in through to give supply to some of the other structures. Okay.

So I did a little bit of blood supply coming here near the endothelial layer. Okay, to give a little bit of nutrition to the actual layers around this area. Okay?

Alright, so that's the cornea. What is important about the cornea? You know the cornea is important for doing what's called, it's helping to actually allow for the light to pass through here. So it allows for the movement of light. So let's say here is actually going to be light.

It allows for light to pass through the cornea. So it's very, very good at allowing for light rays to pass through. Okay, so that's one function of the cornea. It allows for light rays to pass through. All right, sweet.

So we've gotten a part of the fibrous tunic, which is made up of the sclera and the cornea. Let's move on to the next part. The next part we said is the vascular tunic. And the vascular tunic is made up of what three components?

The choroid, the iris, and the ciliary body, which is made up of the ciliary and the ciliary process. Let's talk about that. Okay, so let's start here first with this big old maroon structure right there. Okay, what is that big old maroon structure right here called?

This one coming down this way, this one coming down this way. That's called the iris. Okay, so it's called the iris. So if you guys have seen it like looking at it from an anterior view, you can kind of imagine it like this. Let's say here's the pupil, which is the hole between the iris.

Like this right here, this is actually the pupil right here. It's a little hole between the iris, right? Around it, you're going to have all of these actual muscles. So this right here that I'm drawing with these lines is supposed to represent the...

Iris and that's made up of a lot of muscles, you know, there's two muscles that make up this right here so again, what is this structure here called this structure here is called the Iris and the iris is actually made up of two different muscles. Okay, so one of the muscles is actually gonna be what's called the dilator Pupillae, okay. So one of them is called I think that's actually I put the pupillae.

Let's put the pupillae. So the dilator pupillae Another one is going to be what's called the sphincter pupillae. The reason why I'm mentioning this is because the dilator pupillae is underneath.

what's called sympathetic nervous system innervation. Whereas the sphincter pupillae is underneath parasympathetic nervous system innervation. So what do I mean here? If the dilator pupillae is activated, it'll cause the actual iris muscle to relax, which will cause what, what will do to the pupil hole. So if you imagine here, let's say that I have the pupil here is expanding.

Okay. It's getting bigger. If it's expanding, that means that it's dilating.

The muscles are going to be causing that dilation of the pupil. That's the job of the dilator pupillae, okay? But let's say for whatever reason, the parasympathetic nervous system fibers are innervating the sphincter pupillae, and it's causing the actual iris to contract and constrict that pupil hole, and it's acting like a sphincter. That's called the sphincter pupillae, okay?

So again, dilator pupillae dilates the pupil. Sphincter pupillae constricts the pupil. Simple as that.

And again, it's made up of a nice muscular layer. So it's made up of muscle there, right? The dilator and the sphincter.

But you know what else is important? It's also pigmented. So it's also having some pigmentation to it.

So it also has pigmentation. It's what basically determines the color of a person's eye. So for example, you might have brown eyes, you might have some hazel eyes, you might have green eyes, or you might have blue, right? And all that's determining these darker colors is just the accumulation of more of this actual pigments.

You know when actually we were born, most of us, almost all of us are born with kind of like a slate gray or bluish pigment. Right? And then over time, the actual real pigment of our actual iris comes out.

Okay? Alright, sweet. So we got the iris.

Then we're going to go into the next one. This big, big structure right here. You see all this part right here?

This whole thing right here. All of this big chunk of muscle right there is called the ciliaris. So what is this big chunk of muscle right here? This big chunk of muscle here is called the ciliaris.

All this right here. This is called the ciliaris. Okay, so the ciliaris muscle, what is it doing?

What happens is, it's actually, I'm going to show you here in a second, it's connected to the lens, all right? So when it contracts, it changes the shape. of the lens.

Okay, here's another interesting point here. The ciliaris muscle is under two different types of innervation. It's under parasympathetic nervous system innervation and sympathetic nervous system innervation. We'll talk about this in more detail when we do what's called the pupillary light reflex, which involves the accommodation reflexes too. But the ciliaris muscle is involved in what's called the accommodation.

So we can even put that, which is basically this changing in the shape of the lens. So accommodation, right? These accommodation reflexes, which is important for distance vision and close vision.

Alright, just to give you a tiny little tidbit, whenever the ciliaris muscle contracts, so here I'll put it like this, parasympathetic nervous system, it actually will cause the ciliaris muscle to contract. When it contracts, you see these little things right here, these little black lines, they look kind of like strings from a guitar. These things right here are called, you can call them two things.

You can call them ciliary zonules, so you can call them ciliary zonules, or you can just call them like suspensory ligaments. Suspensory ligaments. Why these are important is because when the ciliary muscle contracts, these, weirdly, these ciliary zonules become very loose. And when they become very loose, what happens is...

This lens starts bulging. So it actually starts bulging. And when it bulges, that's for a very, very close vision.

So short distance vision. But if the ciliary muscle relaxes, so because of what system? This would be the sympathetic nervous system. The sympathetic nervous system actually relaxes the ciliary muscle.

So it relaxes it. If it relaxes it, weirdly, the ciliary zone will become really tight. And when they become really, really tight, It actually causes this lens to flatten and when the lens flattens that's for very far distance vision.

So we'll talk about that when we get into the specifically the pupillary light reflex. Okay, just introducing a piece of it now. Alright, cool. Now, what's the other part? So we've got the iris, we got the ciliaris, there's these little cells here.

Okay, see these tiny little cells here that's kind of lining right over the ciliaris muscle. So there's some cells right here and there's some cells right here. These little bad boys right there, these are called your ciliary processes. So what are these little structures they're called?

They're called your ciliary. processes and they're a tiny little layer of epithelial cells so they're a tiny little layer of epithelial cells epithelial cells some sort of cuboidal epithelial cells right and what they do is they secrete that humor that aqueous humor so they secrete what's called that aqueous humor okay so look what happens here They secrete this humor. So they're going to be making this aqueous humor because there's going to be nearby blood vessels. So they're going to be having blood vessels serving this area. So if you imagine it for just a second, let's say I remove out this part here, and I put a little blood vessel in here.

Because there's going to be blood vessels running all in this area. It gives off little connections. It gives off little connections.

And what happens is these ciliary processes can take some of the substances from the blood and make this aqueous humor. Now what happens is this aqueous humor. And these cells could be over here too, right?

So they could even have some lining this side too. I'm just showing it here. What happens is, let's actually kind of bring this stuff up here.

It moves upwards and as this aqueous humor starts moving, it actually comes up through the back of the iris, right? Comes up the back of the iris. And then it moves through this little hole here. What is this hole here called? The pupil.

And it moves into this little chamber right here, which we're going to talk about later. And then from here, it can provide some certain types of lubrication to different structures. structures in that area and can pick up metabolic waste and it can drain into this little hole right here.

That hole is called the canal of sclim or slim or you can I like to call it the scleral venous sinus because it just sounds weird. Sounds like I'm saying something like I shouldn't be saying right. So again this structure here is called the scleral venous sinus or the canal of sclim. Okay, and so again what happens the ciliary processes are making this aqueous humor moves up through the you know There's actually a chamber here. I'll mention it now.

I might as well because I'm already talking about what is this chamber here? There's two chambers here. There's a chamber here and a chamber here this whole thing though If I were to make this whole distance here, let's do this in pink So it's nice and bright here this whole distance here from the cornea all the way to the lens So from the cornea all the way to the lens There is a specific, this whole thing is a segment.

What is this segment here called? This segment is called the post, I'm sorry, posterior. This should be anterior segment.

Anterior segment. Now, there's two chambers of the anterior segment separated by the iris. This chamber back here is called the posterior chamber. And then this one right here is actually called the anterior chamber. Now truthfully, it's hard to show it in this diagram here, but what happens is this lens is actually much, much closer here.

And the ciliary processes, whenever they're secreting this aqueous humor, what happens is the ciliary muscle has to contract to kind of move the shape of the lens a little bit, so that this aqueous humor can move underneath the lens. And then from the posterior chamber it moves into the anterior chamber through the pupil. Then from that it goes into the anterior chamber and moves from the anterior chamber and drains into this area here.

This little hole here called the scleral venous sinus or the canal of Schlemm. Okay, just so that we got that. So the flow of vacuous humor is still the processes are secreting this humor. It moves kind of underneath the lens. because the ciliary muscles have to actually control the accommodation reflex to allow for it to move underneath the lens.

Then it moves through the pupil hole. It moves from the posterior chamber into the anterior chamber through that pupil hole. And then it drains into the scleral venous sinus. All righty. Sweet deal.

Okay. So let's just recap this real quick because we basically covered these parts here. We got one more layer. But again, sclera.

It has episclera, sclera proper, and lamina fusca. And if I'm being very specific to kind of go along with this, how I said that the cornea had an outer layer to inner layer, this would be the same thing. So from outer to inner layer, we're moving downward.

So the outer layer is the episcalera, then the middle layer is the scleropropa, and then the innermost layer is going to be the lamina fusca. Alright, sweet. Now let's go on to the next part of the uvea or the vascular tunic. One more part here.

Alright, so this posterior extension that's coming from the ciliary body, see this posterior extension here? That's moving all here, this maroonish like structure here. This is all called the choroid. It's called the choroid.

So what is this structure here called? This structure here is called the choroid. Now the choroid is important because the choroid is actually going to be a very pigmented membrane. So it's a pigmented membrane.

Now I'm mentioning that because that has an important physiological function. When light rays, because you know light rays are coming from many, many different directions through here. When the light rays are coming out here and they could be hitting different parts of the retina, this light rays could actually be scattered throughout the ion, which can cause different problems with vision, right? We don't want that. We don't want this actual light to be scattered through all different areas because it could affect the visual field processing.

So what happens is the choroid absorbs some of those light rays that are being reflected, okay? So what is this guy doing here? What is this choroid doing?

He's basically absorbing of light because that could affect the actual visual pathway and what we see within our visual fields we don't want that also really important I'm gonna do it in red it has a nice sub vascular supply a lot of blood that are running in this area. Okay so it has a nice little vascular supply. Okay so very rich in vascular supply which is going to nourish a lot of different structures including the retina. So it's actually gonna have a nice vascular supply that can give blood supply to the retina.

it's going to be a pigmented membrane which can absorb a lot of different light rays to prevent the reflection of that light and the scattering of those light rays. So that we have very, very precise and very, very good visual pathway without any different types of illusions or anything that could come from it. Okay. All right.

Sweet. So we covered that now. All right.

Now let's move on. Let's get rid of these light rays here. Let's move on to the next part. What's the next part? So we've covered what?

We've covered the fibrous tunic. This part's done here. We covered the vascular tunic. That part's done there.

Now we're going to cover the sensory tunic. So the sensory tunic, which is actually going to be consisting of the retina, and we said that we wanted to talk about something else here. All right, if you look here, we were going to talk about this vitreous humor.

From here, if you look here from the back of the lens, go from the back of the lens, the posterior part of the lens, all the way back to the retina. Okay. So all the way back to the retina.

This whole thing makes up another segment. So the anterior segment was from the anterior part of the lens to the cornea. This segment, the posterior segment, is going to be from the posterior part of the lens all the way back to the retina.

Now, I talked about, shame on me, I talked about the ciliary zones and suspensory ligaments, but I didn't really talk about the lens. I said that it's important for basically helping to refract light rays and helping to control our distance vision and our short, close vision. But I didn't really talk about it enough.

So let me actually just real quickly talk about this. This is actually the lens, right? Now, what's important about the lens?

We said it's responsible for refracting light rays. So whenever light is coming in here, it helps to be able to bend the light, right? It helps to be able to allow for the focus those light rays specifically onto the retina. So it's helping to refract these light rays, okay? So that's one of its functions.

But the lens is actually made up of different things. If I were to say here we have the lens, there's actually two components of the lens. The lens is actually consisting of what's called crystalline, like protein molecules. They call them crystallines, which are just proteins.

And that makes up what's called the lens fibers. So the lens fibers is actually going to be made up of crystalline proteins. And then you have another component, which is called the lens epithelium.

Epithelium. And this is actually going to be consisting of some like cuboidal epithelial tissue cells. So it's actually going to have a little bit of cuboidal cells.

Okay. So it's called cuboidal cells. So this is important to understand that the lens is actually made up of two things.

What is the lens made up of? It's made up of lens fibers and lens epithelium. Okay, two components here. The reason I'm mentioning this with this whole lens fibers and the crystalline proteins is because in certain situations there is a, you've probably heard of it, called cataracts. They're called cataracts.

And cataracts are basically just accumulation or clumps of these crystalline proteins. You know, cataracts can be due to many things. One of the common causes is diabetes. So, in people who have diabetes, this could actually be a cause. Smoking actually accelerates this process.

And what else? It could even be congenital. So sometimes just congenital.

You know another weird one? It doesn't make any sense, but it could be due to if you consume too much vitamin C. So if you take too much vitamin C, like through supplementation, I actually take vitamin C, that's why it's weird. If you actually take too much vitamin C, this could actually accelerate the... Process of cataracts too.

So it's an unfortunate thing here, right? So that's why I'm mentioning the lens because there is certain clinical correlations that whenever there's accumulation of these crystalline proteins, it can cause cataracts, which can definitely make a huge difference in your vision because what is it responsible for? helping to refract some of those light rays onto the retina, to focus those light rays onto the retina, to help with our distance vision and our close-up vision.

Okay? And you can actually do surges to replace the actual lens nowadays. So that's pretty cool.

Alright, so we covered the lens. Now let's get back to the posterior segment. Sorry for being off track there. Okay, now in the posterior segment it's gonna be made up of all of this pink stuff. Now what's interesting about this pink stuff here is that you make it during embryonic development and you never make any more of it for the rest of your life.

Whatever you have, that's what you got forever. So what is this jelly-like material here called? Which it has some types of proteins also within it.

as well as other different types of molecule like hyaluronic acid and stuff like that. What is this substance here called? This whole substance pretty much occupying the entire posterior segment is called the vitreous humor. So pretty much this whole posterior segment is occupied by the structure called the vitreous humor. There's actually a remnant like structure that can actually run through here called the hyaloid canal.

We're not going to mention it, but it can actually run right within the vitreous humor. We're not going to talk too much about it. Just saying that there is another structure that can run in it, the posterior segment, which is called the hyaloid canal. But primarily, it's going to be made up of this vitreous humor. Now.

What's the function of this vitreous humor? What does it do? Well, the vitreous humor is really good at being able to transmit the light rays. So it's good at transmitting the light rays.

So any light rays that are coming in here, this vitreous humor is very, very, very good at being able to allow for the light rays to move through that jelly-like material and onto the retina. Also... It's very kind of like a strong jelly-like material. So it actually, you see how right here we have this like black lining here?

This black lining here with all this like baby blue underneath it, all this part here, the black line, all the way back to that brown line there, this is going to be made up of the neural layer of the retina. So we'll talk about these two things. There's two parts of the retina, the inner neural layer of the retina and the outer pigmented layer of the retina.

What this actual vitreous humor does is it holds the retina. together so it holds the retina the neural layer and the pigmented layer close to one another okay so it holds the neural layer and the pigmented layer close to one another that's another function so it holds retina in place and notice another thing that we didn't really talk too much about what we talked about in other videos you know what's actually connecting over here on the eye like for example let's say that I have a muscle right here the inferior rectus. Let's say that I have a muscle back here, up here I mean, superior rectus. And then you have other ones, medial rectus, lateral rectus, all those different muscles, right?

What are they doing? They're called extraocular eye muscles and they're changing, you know, they're moving the eyes. Whenever these extraocular muscles are contracting and pulling on the eyes, they can change the intraocular pressure.

But you know what the vitreous humor is very, very good at doing? It's helping to maintain, it's contributing to the intraocular pressure to prevent any excessive. Changes in the intraocular pressure that is occurring whenever these extraocular muscles are contracting. So again, one more time.

When the extraocular muscles are contracting, the vitreous humor helps to be able to maintain the actual intraocular pressure. That's its function. When the extrinsic ocular muscles are contracting, it helps to maintain the intraocular pressure.

So we can say it contributes to, I'm going to put intraocular. pressure, IOP. Okay, so it contributes to intraocular pressure. Sweet.

Now we get on to the freaking good stuff, the meat and potatoes. All right, so let's talk about this one right here. We're going to actually zoom in on it later when we go through the layers of the retina, but I'm just going to take a tiny little piece out for just a second here.

So let me pretend that I'm doing this for a second. I'm taking a slice of this, a little chunk of this right here, and I'm going to zoom in on it. Okay, I'm going to take a little chunk of that and I'm going to zoom in on it. Let's come over here for just a second.

Alright, so let's say right here, let's say that this is that actual part there, and that was kind of separating, what would this structure be right here? This would be where the vitreous humor is. So let's say this is where the vitreous humor is. Okay, that's all vitreous humor. Then there was the part of the retina that we had here in blue.

All this part here. What is this made up of? What is the retina made up of? We'll go over its cell layers in more detail, but I'm going to give you a brief little discussion in it. Very, very brief.

This is the outer pigmented layer of the retina. There's two parts of the retina. Okay.

What is this blue layer here called? This blue layer is the inner neural layer of the retina. The neural. layer of retina.

This is made up of three different types of cells. Well, there's actually more. We'll discuss these in more detail like I said, but there's gonna be what's called photoreceptors.

Photoreceptors and these are like your rods and your cones. There's gonna be what's called bipolar cells or bipolar neurons. There's gonna be what's called ganglion cells and then there's gonna be what's called amacrine. and horizontal cells which are basically helping to modify the visual pathway. So a lot of different cells within this area that are making up this neural layer of the retina.

Photoreceptors which are consisting of rods and cones, bipolar neurons, ganglion cells, and amacrine and horizontal cells. This is important because we talk about photo transduction we'll see this flow. Okay, so that's make up in the neural layer of the retina. The next one that we said this brown layer is the outer pigmented layer of the retina.

So this is the outer pigmented layer of retina. And this is actually made up of these actual epithelial cells. These epithelial cells, so it's actually made up of epithelial cells, kind of like a single layer of epithelial cells, rich in melanin. Very rich in melanin. And that is important for basically being able to help to contribute to preventing the scattering of light rays.

So it absorbs some of that light to prevent the scattering and the actual reflection of these different types of light rays. Another thing, what do we say it runs right around this area? The choroid.

So the choroid runs in very, very close proximity to this actual... Outer pigmented layer. Why is that important?

Because you see these epithelial cells that are actually rich in melanin. We call them pigmented epithelial cells. These pigmented epithelial cells, they basically act like kind of like the part of the blood brain barrier in a similar way. These cells here, they filter whatever is actually coming out of this choroid vessels and determine what actually goes into the retinal area. Okay, so these cells here that are making up this outer pigmented epithelium, they're very special and the reason why is they're controlling what's leaving the blood from the choroid vessels and coming out here into the neural layer of the retina.

The reason I'm mentioning this is because in certain types of severe trauma or shifting of movement, you can actually kind of dissect this layer here, kind of dissect this layer right here. And when you dissect this layer right here, what can happen is... Some of this vitreous humor can actually leak in between these spaces. So some of this vitreous humor can leak in between these spaces. When some of this vitreous humor leaks in between the actual neural layer of the retina and the outer pigmented layer of the retina, that's called a retinal detachment.

And if not treated very quickly, it can lead to blindness. Okay? So in certain situations in which there is the separation of the inner neural layer of the retina and the outer pigmented layer of the retina, Vitreous humor can come into that little space and cause retinal detachment. And if not treated quickly, it can lead to blindness.

Alright, that's that part. One other thing I want to mention here. Let me actually get rid of this part here.

Because I want to mention something else with relation to the eye. I'm going to draw another mini eyeball here real quick. Another mini eyeball.

Because I want to talk about these things called your eyelids, your palpebra. So let's see here, I draw another mini eyeball. Here's the actual cornea. Here's the pupil and then here's your optic nerve, right? We're not going to draw everything in there.

It's not super important. Affricate, we'll do it real quick. Do this here and then that there. Okay? Now, coming right around this area, you're going to have the lower eyelid.

So you're going to have a little area right here called the lower eyelid. Then coming over here, you'll have another one which is going to be the upper eyelids. actually make this one look like that one actually do it like this okay so look you'd have some beautiful eyelashes coming off there and some beautiful eyelashes coming off like that right why am I mentioning this two things one there's a little layer here let's do this one in orange orange There's a little layer here lining right underneath this thing. What do we call this? We call this the palpebra.

So this is the inferior palpebra, the lower eyelid. This is the superior palpebra, the upper eyelid. There's a little tissue here that's lining not only the eyelid, but it's giving off a little double-layered membrane here that kind of covers a little bit of the cornea. Okay?

So there's a little layer here that's actually covering underneath the palpebra. And then there's a layer that's actually covering onto the bulb of the eye here. A little bit on the bulb of the eye. So again, same thing over here. There would be a little layer here covering the inner surface of the palpabra and then giving off a little layer here that kind of covers a little piece of the cornea, like the bulb of the cornea, right?

What is this called? This is called the conjunctiva, right? So this part here, that part there that's actually lining the inner part of the palpabra, that's called the palpabral conjunctiva.

Palpabral. Palpa. Broll, conjunctiva, and then this inner one here that's actually lining the little parts of the cornea there, that's called the bulbar conjunctiva.

Okay, the bulbar conjunctiva. The reason why I mention that is that certain bacteria or viruses can accumulate in this area. People always joke around and say like, oh dude, I'm going to fart on your pillow and you're going to get pink eye. It's partially kind of true if certain types of bacterial molecules or viral molecules get into that little space there and cause inflammation and infection of that area that can lead to what's called conjunctivitis, pink eye. Right?

And that's why it's important to know a little bit about that is that if there's the inflammation of the palpebral conjunctiva and then the bulbar conjunctiva this could lead to what's called pink eye or conjunctivitis. Alright? So don't go farting on people's pillows and stuff, all right? Now, next thing. There's another two more important structures in here.

Right in here, if I kind of draw it in black here, there's a little plate. A little plate right here. It's called the tarsal plate. So what is that little thing I'm making like a U?

That's called the tarsal plate. This has two functions. One function is there's two muscles that connect to it.

One muscle is called the actual. the palpebra muscles right so for example you could have the palpebra muscles if there's one up here that'd be a connection of the levator palpebra superioris also it's also a nice connection for the orbicularis oculi so two different muscles can attach to the tarsal plate right so if i kind of draw it like this over here too say i draw it like this i bring it like this right here right there's a tarsal plate right there and again there you have the levator palpebra superioris attaching and then the orbicularis oculi attaching. Okay, that's one function of the tarsal plate. All right, so there's two muscles that are attaching to the tarsal plate. One could be the orbicularis oculi.

And if we were to be really specific, there would be another one that's actually attaching up here called the levator palpebra superioris. Okay, so this one up here would be the Levator palpebrae. I'm not going to write all at levator.

Palpebrae superioris. Alright, that's one function of the tarsal plates. Another function, there's these actual glands in here called the tarsal glands. So there's glands kind of like inside of that tarsal plate there called the tarsal glands. What happens is these are basically like sebaceous glands and they produce kind of like oily secretions on the eyelid to keep the eyelid and some of the structures on the eye nice and moist and prevent basically the eyelids from sticking together or sticking to the eye okay or the cornea in this case so there's little tarsal glands inside of the tarsal plate that producing sebum and oily secretion to basically keep the palpebra nice and lubricated prevent them from sticking together and prevent it from sticking to like the corneal area okay all right guys i just wanted to take in a little bit of time and pre-draw this structure here because i want to talk really briefly about the lacrimal flow okay because that's kind of important so Lacrimal flow are basically the production of tears which is what Conor McGregor is going to be doing when he fights Floyd Mayweather on August 26. Alright, anyway what happens here if we look at an anterior view of the eye here's your upper palpebra the superior palpebra here's the inferior palpebra you see this kind of like V like part here that V like part there is actually called the Lateral commissure and this part over here is actually called the medial commissure.

But don't get that confused with the space between the superior palpebra and the inferior palpebra. That's actually called the palpebral fissure. Okay so this little V part over here is actually called the lateral commissure.

V part over here is the medial commissure and the space between the palpebra is called the palpebral fissure. Now this right here is the eye. I'm just showing an anterior view of the nose like this is the nasal septum.

And this is the lateral wall of that nose, and this is the lateral wall of that nose. Okay, that side of that nose. All right?

Sweet. So let's go here in a step-by-step process. First thing is the lacrimal glands.

If you remember the facial nerve, the facial nerve, cranial nerve 7. Cranial nerve 7 was actually one of the big guys there that was going to innervate this guy. All right? And cause this actual lacrimal gland to start producing lacrimal fluid.

And that lacrimal fluid, if you remember, it comes out. and moves across the eyeball. So it moves across the eyeball, nourishing the cornea and basically picking up any types of metabolic waste products.

And it starts moving medially towards that medial commissure. There's actually a little fleshy part here. A little fleshy part here actually called the lacrimal caruncle. A little area right there called the lacrimal caruncle, little fleshy part there. What happens is, there's these tiny little holes here.

Tiny little holes right there around that medial commissure called the lacrimal puncta. So the first step is that lacrimal glands secrete it. They move medially. Then the third step is they move into this hole here called the lacrimal puncta. Then from there, they move through these tiny little canaliculi called the lacrimal canaliculi.

Then from that, they move into this big old sack here called the lacrimal sack. Then the lacrimal sack empties. This stuff through this duct here called the nasolacrimal duct and it goes underneath you see how this is the superior concha, superior nasal concha, middle nasal concha, inferior nasal concha and in between it this is the superior meatus, middle meatus and inferior meatus.

The nasolacrimal duct empties in just around the inferior meatus into the nasal cavity. Okay so to recap that what's it all doing here first one lacrimal gland secretes. Okay, fluid. Second step, moves across cornea medially.

Then third step what? Goes into the lacrimal punta. Moves into lacrimal punta. Then fourth step, goes through these tiny little canaliculi. Then it goes into the lacrimal canaliculi.

Then from there it goes into the lacrimal sac. Then from there it goes into the nasal lacrimal duct. And then from there goes into the nasal cavity through the inferior meatus.

So I'm going to put inferior meatus of nasal cavity. Holy sweet goodness we did it. Alright. Now, one more thing I want to talk about and then we're gonna go ahead and stop. Alright.

There's another little thing that I forgot to mention here, probably one of the more important things here, is that if you're looking here you see this whole big sucker right there? What do you think this is? This right here is called the optic nerve. Okay. This is called the optic nerve.

So what is this structure here called? It's called the optic nerve or cranial nerve. This is also called cranial nerve 2. The reason why I'm telling you that is because if we look at the eye, if you do what's called an ophthalmoscope, so you look at the eye from actually doing an ophthalmoscope, you look into their eye, you're going to see in the back of the eye, you're going to see this structure here called the optic disc, that little part there. The optic disc is where the actual optic nerve is piercing through the back of the sclera. Then you'll see kind of a little bit near it, you'll see another structure called the eye.

Maculae, right where the fovea centralis is, where the highest concentration of cones are. Okay? But right here is the optic disc.

So if I do what's called a fundoscope, you are looking at the back of the eye, there's the optic disc and there's what's called the macula lutea, kind of a little bit more lateral to that. The optic disc is where the actual optic nerve pierces through the back of the sclera. Now when I say it pierces through the black of the sclera, we said, oh wait, I thought the sclera was the episclera, the sclera proper, the lamina fusca. Yeah, it gives a little extension downwards here. And whenever the optic nerve is piercing through the back, it moves these little holes.

So the optic nerve, which are the axons of the ganglion cells, they're moving through these holes. What are these holes here in the sclera called? These holes in the sclera are called the lamina cribrosa. Cribrosa, okay? And it's running, it's these little holes within the sclera where the optic nerves are piercing through the back.

All right. All right, Ninjas, we covered a lot of information in this video. I really hope you guys enjoyed it. I hope it made sense. If you guys did like it, please hit the like button, comment down in the comment section, and please subscribe.

In the next video, we're actually going to take a look more specifically at the retina, zoom in on the retina, all the cells of the retina, and then talk about the phototransduction process. I hope to see you guys there. All right, Ninja Nerds, until next time.

Transcript for:Comprehensive Overview of Eye Anatomy

Transcript for:
Comprehensive Overview of Eye Anatomy