let's now take a look at the basic anatomy and a little bit of physiology on the eyeball so the first thing is that the reason why we have an eye so that we can produce a good picture on the surface of our retina and so our retina will take up predominantly the posterior portion of the eyeball itself and we'll get to the retina but first thing we need to be aware of is when we look at the eye and atomically there's three main layers that you need to be aware of so we're going to go through these three layers and we're going to start with the outermost layer so let's write this up number one outermost layer now let's call it the outermost coat or outer coat and what the outer coat first of all is there for so it's function is for protection so you can write out a coat protection now the outer coat is made up of two particular parts first part is something called the sclera and the second part is something called the cornea so the sclera is basically this portion of the eye that's the sclera now if you want to have a look into the mirror the white part of your eye that's what we return the sclera and that's what we're referring to here this makes up if you look at the surface of the eyeball the sclera makes up around about 93 percent of the surface of the eyeball the cornea is this part of the eyeball here and that makes up around about seven percent of the surface of the eye so just to put yourself into a frame of reference this is the anterior aspects of the front of the eye this is the posterior aspects of the back of the eye and what I just said was that this is the sclera and that this is the cornea and these are the two parts that make up the outermost portion of the eye sclera cornea what are they there for well I said first of all protection that's true the sclera you're gonna find is quite smooth this is important because the sclera sauceless also the side of attachment for extra ocular muscles and these extra ocular muscles when they contract they're going to shift the eye in various directions so the sclera needs to be smooth scorer also has a number of little holes in it for blood vessels as well it's made up of a type of epithelia the cornea where the couny is made up of about five layers and the outermost layer is also epithelia as well and the cornea if you have a look at it it's transparent this is different to the sclera which is not transparent it's opaque so let's write that down that the sclera is opaque which means it's whitish and the cornea is opaque sorry and the cornea is transparent now the question is why is this the case what reason is this because we want to produce an image and we want to produce a good image and this occurs when light comes into the eye and hits the retina or at least the photosensitive parts of the retina which are the cones Rod's for example and creates an image the way this light gets in must be just via the cornea it can't get in through the sclera because the fact that it's opaque so because of its color because it's white light cannot go through that's important but because the cornea is transparent light can get through and so it's very specific light coming from a very specific direction getting into the retina that's very important when we look at the sclera and the cornea you'll find that there is an apart where the cornea becomes the sclera what we call the cornea scleral Junction now you can call it the cornea scleral Junction and again it's this part right here the cornea scleral Junction I'll just make it a little bit I'll just highlight a little bit more there we go cornea scleral Junction right there it's also known as the limbus so the limbus is the cornea scleral junction and one important point about the limbus is this I told you that the outermost layer of the five layers of the cornea is epithelia this epithelia cannot regenerate itself it can't produce its own cells so there needs to be a stem cell population for epithelia somewhere and its location is here at the limbus which means that they produce new epithelia and they migrate across to cover the surface of the cornea I'll do an entire video on the cornea in those five layers okay so this is the outermost layer made up of the sclera and the cornea let's go to the inner most layer so number two so the inner coat so I said the outer coat was there for protection the inner coat is there for vascularity and nutritive purposes so it's there to deliver a blood supply which has oxygen and nutrients available so we can write since it's going to be blood vessels let's use red inner coat is vascular and nutritive and there's three particular parts to the inner layer the first part that we're going to talk about is called the choroid now the choroid covers the inside of the sclera like this so it covers the inside of the sclera and what you find is that the choroid as it moves more anteriorly it starts to thicken and one remember the choroid is a thin highly vascular layer again delivering nutrients delivering oxygen and so forth as it gets a bit more anterior to the eyeball it starts the thicken and as it thickens what you'll find it starts the thicken and it produces these to thicken portions here called ciliary bodies so this one here is a ciliary body now why do we have a ciliary body well the ciliary body has ligaments attached to it like little strings little anchor points and what these little strings or anchor points do is that they are attached to the lens of the eyeball so you're gonna find that you're gonna have all these little strings coming off called ciliary ligaments and they are attached to the lens okay now we aren't done here with the vascular portion which we've got here for the inner coat we've got the chloride we've got the ciliary body and the last part is called the iris now the iris has another name that other name is diaphragm but it is the iris so the three parts of the innermost layer you can say are the choroid you can say is the ciliary body or bodies and then the last part is the iris now the iris what you'll find well a couple of things firstly the ciliary body has muscles associated with it and what these muscles do is since they're attached to these ciliary ligaments here we'll these suspensory ligaments which are attached to the lens right here remember it's the lens that can focus that light so depending on the strength of a pull of these ciliary ligaments which are attached to the ciliary bodies it changes the shape of the lens which means if you need to focus light from a further distance or closer that lens may need to be more concave or that lens needs to be more flattened and this has to do with the muscles of the ciliary body but in addition to that the lens or the diaphragm here can also change its diameter and it's called the diaphragm and it can change its diameter and again let through only certain amount of light through this gap here this gap here is called the iris aperture but is also referred to as the pupil iris aperture also known as pupil okay so these are the three different aspects of the inner coat the third coat which is called the sorry does keep saying inner coat meant to say middle coat I'm so sorry that's the middle coat number three is the inner coat I do apologize obviously the inner coat is going to be the most inner portion this is basically the retina now what you gotta find is that the retina is made up of two particular layers okay it's actually made up of more layers but I'm going to refer to it as the inner layer and outer layer so the outermost layer is going to be that that's closest to the choroid and this is called the pigment layer so we can say outer is pigment layer and the inner is called the neural layer okay so the pigment layer has pigmentation such as melanin and what you'll find is that this pigmentation or this pigment layer of the retina goes is attached to that chloride silly everybody and lens so all of these areas of pigmented now that's important when it comes to when you look into the eye and you see the dark portion of the pupil that has to do with the pigment of the iris and of the ciliary body that's the dark that you are looking at when you're looking in okay so this is the pigment layer that I've got here I'll draw an arrow like this that's the pigment layer and then the next layer is the neural layer I'm gonna draw the neural layer now the neural layer does not go all the way to the anterior portion of the eye stops around about there so maybe around about four-fifths of the posterior portion of the eye is where the retina goes to them this is important because the outer layer which is the pigment layer does not contain the photosensitive cells of the eye the inner layer which is this neural layer does contain the photosensitive cells of the eye so what does that mean let's just highlight it so this neural layer contains the photo sensitive cells now these are the cells that have rods and cones for example I'll do a whole lecture talking about the specifics of rods and cones but they are what transduce light into electrical energy that we can send to the brain to make sense of what we saw so the neural layer is what contains the photosensitive cells not this pigment layer which means that you've got an area this anterior area of the eye here that cannot pick up light therefore it cannot pick up an image and send it to the brain now there's some other parts of the eye that I very quickly want to talk about first is the two types of humor now that's the fluid that's sitting in the eye you got the floor that sits in the main body of the eye and that actually contains the predominant mass for the eyeball and then there's the floor that sits in the anterior portion of the eye okay so at the back go throughout the main body of the eye this humor is called the vitreous humor the vitreous humor now the vitreous humor is well it's predominately water with a bit of electrolytes basically it's a gelatin gelatin jelly like substance but it's predominately water and some electrolytes if we look anteriorly you're going to have more humor sitting here and this is going to be called the aqueous humor now the aqueous humor is actually produced by the cells there per filial cells that sit at the anterior portion of the ciliary body okay and in actual fact what these cells do when they produce this aqueous humor they start to move through the posterior chamber and then they move their way to the anterior chamber and what happens is this humor this aqueous humor needs to be drained needs to be drained on a daily basis and where does it get drained into it gets drained into this lymphatic vessel that sits around about here now this lymphatic vessel should dry in this aqueous humor away if it doesn't it means that aqueous humor can start to accumulate in this pond Tyrael posterior chamber of the eye here and what that leads to is increased intraocular pressure and this can result in glaucoma okay so what have we gone through have gone through the three major layers of the eyeball first layer is the outer layer and that's made up of the sclera which is the white of the eye and the cornea which is the front transparent disk of the eye then you've got the middle coat which is made up of is the vascular section it's the nutritive area as well so it feeds the eyeball and it's made up of the choroid which is a thin vascular blood supply the ciliary bodies which are a thickened area that produced the aqueous humor and are attached to choroid sorry ciliary ligaments which connect to the lens which help the lens maintain its shape or even change its shape and we've got the iris as well which is a diaphragm that can change the aperture diameter which changes how much light can get into the eyeball itself the inner coat is the retina which is made up of many layers but I've said that there's two major layers you need to be aware of the innermost layer which is the pigment layer this contains melanin melanin and when we look at the pigment layer as we go to the ciliary bodies and iris that's what you see with the darkness of your eyes and the color of your eyes and when we look at the neural layer the neural layer only takes up the majority posterior portion of the eye and this is the layer that contains the rods and cones that we can pick up light and turn into some form of neural energy so information that can get to the brain and tell us what we've seen so that is a quick run-through of the basic eyeball anatomy