0:00 In this video we will look at the anatomy of the eye and overview. 0:10 So here we begin with the cross-section of the eye. 0:13 We have the conjunctiva, the cornea. 0:19 The cornea is on the same layer with the sclera, which is at the posterior end 0:23 of the eyeball. 0:26 The iris surrounds your pupil. 0:28 The iris makes the color of your eye and is responsible for changing the size 0:33 of the pupil 0:35 through its two muscles. 0:38 So here is the pupil, the black part of the eye, which captures the image you 0:42 are seeing. 0:43 Behind the pupil are the lens, which can change shape. 0:49 The primary refractive structures that bend the incoming light has to focus the 0:54 image on 0:54 the retina. 0:56 These primary structures are the lens and cornea. 1:00 So these are the main structures basically responsible for bending the incoming 1:04 light 1:04 to focus on the retina at the back. 1:08 So the layers of the eye on the posterior aspect from the outside, we have the 1:15 sclera, 1:16 then the choroid. 1:17 Within the same layer of the choroid are the ciliary bodies. 1:21 The choroid, ciliary bodies and iris make up what is known as the uvia. 1:28 The inner layer of the eyeball is the retina, which contain the photoreceptors. 1:33 The retina has a section called the fovea. 1:38 The fovea is a small central pit composed of closely packed cone cells, the 1:44 cones in 1:45 the eye, and cones are your photoreceptors. 1:50 The retina captures images through the photoreceptors. 1:53 These images then get sent along nerve fibers that travel through the optic 1:58 disc and form 1:58 the optic nerve, which is your cranial nerve number two. 2:03 Other structures that pass the optic disc are the retinal arteries and the 2:09 veins. 2:10 So what is inside the eyeball itself? 2:12 Well, there is a fluid inside the eyeball, this fluid is called the vitreous 2:18 humor. 2:19 We say the vitreous humor occupies the posterior cavity of the eye, and we will 2:24 learn about 2:24 the anterior cavity next. 2:28 But before going into the anterior cavity and the posterior cavity as well, let 2:33 us just 2:33 recap the basically layers of the eyeball. 2:37 So the wall of the eyeball is made up of three layers. 2:43 So the first layer is basically the fibrous sclera and the cornea, which is in 2:48 the same 2:49 layer. 2:50 The second layer is the choroid, the iris and the ciliary bodies, which make up 2:55 the oovia. 2:57 I think I pronounced that, right? 2:59 And then the third layer is the retina, which contains your photoreceptors, the 3:03 rods and 3:04 the cones. 3:08 So let us zoom into the anterior section of the eyeball here. 3:14 So here is the anterior section of the eyeball. 3:17 There is the posterior cavity and an anterior cavity. 3:22 The posterior cavity is separated from the anterior cavity by the lens. 3:29 So here is the lens. 3:31 So here the space anterior to the lens is known as the anterior cavity. 3:37 And the posterior cavity, as I mentioned, contains the vitreous humor. 3:43 Here are the ciliary bodies and coming off the ciliary bodies and connecting 3:48 the lens 3:48 are suspensory ligaments. 3:51 Thus, we can say that the ciliary bodies are responsible for the shape of the 3:58 lens. 3:59 And we will learn about this later on. 4:01 But keep note of that. 4:04 So here is the iris, which is the color bit of your eye and the iris contains 4:08 muscles 4:09 which contract or relax and is responsible for how big your pupil is and thus 4:15 how much 4:15 light is entering your eye or hitting your retina. 4:19 Okay, now let us talk about the anterior cavity, which, as I mentioned, is 4:25 separated 4:25 from the posterior cavity by the lens. 4:29 But the anterior cavity can be further divided by the iris into the anterior 4:35 chamber and 4:37 posterior chamber. 4:40 The anterior cavity, unlike the posterior cavity, contains a fluid called the a 4:45 queous humor. 4:47 The aqueous humor carries nutrients for the anterior structures of the eye. 4:54 The aqueous humor is produced by the scapillary network within the ciliary 4:58 bodies, then drain 5:00 into the canal of schlem before entering the blood. 5:04 Canal of schlem is also known as the scleral venous sinus. 5:11 So here we can see the aqueous humor produced by the ciliary bodies and it 5:14 drains into the 5:15 canal of schlem. 5:17 This canal is important because obstruction of the aqueous humor drainage can 5:23 lead to 5:24 a eye condition called glycoma. 5:27 And this is because pressure essentially builds up as fluid as the fluid cannot 5:32 drain out. 5:34 And so this will lead to glycoma, which can damage the eye's optic nerve and 5:40 can result 5:41 in vision loss and blindness. 5:48 Next let us learn a bit about the iris and pupil and its innervations. 5:53 So here is the eye from the front. 5:56 The sclera is the white part of your eye. 5:58 The pupil is the black part of the eye where light enters, surrounding the 6:05 pupil is the 6:06 iris. 6:07 And the iris is the, remember the color of the eye, and the iris controls the 6:12 size of 6:12 the pupil and thus adjusts the amount of light entering the eye. 6:17 Now let us look at two scenarios where the pupil constricts and relaxes. 6:25 So pupillary constriction and pupillary dilation. 6:31 Remember the iris has two muscles. 6:33 These are the sphincter muscles and the dilator muscles on the outside. 6:38 The sphincter muscles are responsible for pupillary constriction. 6:42 And these sphincter muscles are similar. 6:46 The sphincter muscles are responsible for pupillary constrictions. 6:50 And these sphincter muscles are stimulated by the parasympathetic nerve. 6:56 Thus sympathetic stimulation causes pupillary dilation through the dilator 7:02 muscles. 7:03 So when you fight or flight response you have dilated pupils so you can see 7:09 more. 7:10 Next topic in this video we will look at accommodation, the lens and silary 7:14 bodies. 7:15 So again just recapping, we have a cross-section of an eyeball. 7:19 The fovea here contains a lot of cones, the photoreceptors, a particular type 7:25 of photoreceptor. 7:27 And where most of the image from the pupil is basically captured, the fovea. 7:32 The fovea is within the layer called the retina. 7:34 And the retina as I mentioned contains the photoreceptors which set information 7:38 to the 7:38 nerve fibers that make up the optic nerve. 7:41 And the optic nerve is cranial nerve number two. 7:45 As light passes through the eye it is bent by the cornea and the lens and is 7:51 focused on 7:52 the retina. 7:54 So here is the cornea and here is the lens. 7:58 These are the primary structures responsible for focusing the light entering 8:02 the eye and 8:03 it focuses on the fovea at the back. 8:06 The lens is an elastic structure consisting of transient fibers. 8:14 Here is a lens but things can happen to the lens. 8:18 The fibers of the lens can become opaque. 8:21 This can result in no light entering the eye. 8:24 This condition of the lens becoming opaque is called cataract. 8:29 Okay, now the greater the lens curvature the more light bends. 8:40 The ability to adjust the strength of the lens is known as accommodation. 8:44 So basically the ability to constrict make the lens tight is known as 8:50 accommodation. 8:51 And let us look at that now by looking at two different scenarios. 9:00 So the strength of the lens depends on its shape which is regulated by the c 9:07 iliary muscles. 9:09 So if you remember your anatomy here is your ciliary system. 9:14 Sympathetic stimulation causes the ciliary muscles, the body is to relax and 9:19 this will 9:20 cause the lens to flatten and weak. 9:24 So it will basically make it relax. 9:31 Parasympathetic stimulation on the other hand will constrict the ciliary 9:36 muscles resulting 9:37 in a rounded strong lens. 9:40 So it's adjusting the strength of the lens for accommodation remember. 9:45 And these changes that the lens can perform by being you know as I mentioned 9:49 round and 9:50 stronger is known as is part of accommodation. 9:54 Okay so how does accommodation work? 9:57 Well if you see an object far away so a far source there is no accommodation 10:03 and your 10:04 lens do not need to change. 10:07 When there is no accommodation the ciliary muscles are relaxed and thus the 10:11 lens are relaxed. 10:13 Despite that enters the eye is refracted by the lens and hits the retina and 10:18 all is good. 10:20 However when your eye focuses on objects close to you so near source you need 10:27 to accommodate. 10:30 There has to be accommodation and this is where the parasympathetic nerve 10:34 causes the 10:35 ciliary muscles to contract and so the lens tightens and the light can then be 10:41 refracted 10:42 more and thus more focused on the retina. 10:47 So I hope that made sense. 10:50 Again normally light is adjusted so that light hits the retina. 10:56 There is a condition however where the lens change with age this is known as 11:00 press biopia 11:01 and this results in a reduced ability to accommodate thus light is refracted 11:08 everywhere 11:09 and doesn't really hit the retina and so vision becomes blurry. 11:14 So I hope you enjoyed this video on the anatomy of the eye. 11:17 Thanks for watching.
