Vision: Eyeball Anatomy (Nursing)

00:01 The eyeball itself has a lot of components that are verging between gross anatomy and microanatomy.

00:09 But a lot of this, we can actually see very carefully with the naked eye.

00:14 So we have a fibrous tunic, which is just what it sounds like sort of a stronger layer, rather than a sensory layer.

00:23 And part of that is the cornea, the part in the most anterior forward facing portion of the eyeball.

00:31 And it's going to give rise to the sclera more laterally, which is the thick white portion of the eyeball that you can see pretty easily.

00:39 There's also the vascular tunic.

00:42 And as the name implies, this is we're going to find vessels because we actually don't find vessels in the fibers tunic.

00:47 That's why the sclera is so white, and the cornea is going to have none whatsoever because you want light to pass directly through the cornea, so it can be sensed by the eye without any sort of obstruction.

01:01 The vascular tunic, will be composed of iris, something called the ciliary body and the choroid layer.

01:12 We also have right there in the middle, another a vascular structure because it's in the direct pathway of light, called the lens.

01:23 And this is where we're going to see some cavities be defined.

01:28 So we have an anterior cavity sitting anterior to the lens, and a posterior cavity sitting posterior to the lens.

01:40 Much if not all of the posterior cavity is occupied by a thick gelatinous structure called the vitreous body.

01:50 And beyond that, we're going to have a more sensory layer called the retina.

01:56 And it's the retina that's going to connect eventually to the optic nerve.

02:02 So let's look again, a little bit more closely at the fibrous tunic.

02:06 So again, most anteriorly we have the cornea, and it is transparent. No blood vessels there.

02:13 And it's so that light can pass through unobstructed.

02:17 The sclera is thick and tough and very fibrous.

02:21 And again, that's the white part of the eye.

02:24 And that's going to go more laterally even back into the aura beyond the area of the eyeball.

02:29 You can see when you're examining the patient, for example.

02:33 And the vascular tunic has the iris and its accompanying ciliary body, and the choroid layer.

02:42 And when we look at the iris from a more anterior point of view, this is the way we're used to seeing the iris.

02:46 We see that the center of it is the pupil.

02:50 And the iris is sort of like the shutter on an old camera, where it can increase or decrease the size of the pupil in accordance to how bright the light is.

03:02 So when lights are very bright, the pupil will constrict.

03:07 Less light needs to pass through if the lights very bright.

03:09 If it's dim, that shutter will open, making the pupil wider so that more light can get in and the ability to visually sense things can be enhanced in low light levels.

03:22 So again, here we have the relationship between the cornea anteriorly and then the iris.

03:28 Just posterior to that is the ciliary body.

03:32 And here's that thing called the lens the other avascular thing that's essentially trying to not obstruct light reaching the retina.

03:41 And we can see between the ciliary body and the lens, it's held in place by something called the suspensory ligaments.

03:48 So it's not just floating around. It actually is held in place.

03:51 So that's right there, just beyond the pupil.

03:55 Now, as we said everything posterior to the lens is called the posterior cavity.

04:00 And mostly this thick substance called the vitreous body.

04:05 And everything anterior is the anterior cavity.

04:08 And that's actually going to have more of an aqueous solution.

04:11 And that anterior cavity is going to be further divided into an anterior chamber, anterior to the iris.

04:20 And a posterior chamber, posterior to it.

04:25 And this aqueous solution is where gases and other things are going to dissolve and basically keep these avascular structures like the lens and the cornea alive.

04:36 Because otherwise, it's very tough to keep things alive that doesn't have a vascular supply.

04:43 So again, here we have the area posterior to the lens.

04:48 And this is the vitreous body.

04:52 And this vitreous humor is a very thick gelatinous substance.

04:58 And it's essentially protecting this layer on the back part of the eyeball, which is the retina.

05:05 And the retina is very complicated.

05:09 And if we go from the outside, inside, we start with the protective portion, which is the sclera, part of that fibrous tunic.

05:18 And then the vascular tunic, which is made up of the choroid.

05:21 This is where the blood vessels come into play.

05:24 Then we have the retina and its various components.

05:28 We have photoreceptors.

05:31 We have these bipolar cells that are sort of transmitting things.

05:35 Then we have the ganglion cells where basically they synapse.

05:39 That's what essentially happens at ganglia.

05:41 You have a synapse of the cells with something else.

05:44 Then eventually, those ganglion cells that have synapse from all of these receptor cells are going to form the optic nerve.

05:53 And that optic nerve will go back into the visual areas of the brain.

05:58 So in the retina, there are different types of receptors.

06:01 So there are the rods that are sensitive to levels of illumination around.

06:07 And they're very good for night vision.

06:10 Then, the cones are better for daylight vision.

06:13 And they're the ones that are really good for color vision.

06:15 And they have these three types, so called red, blue, and green.

06:20 They're concentrated in a particular part of the retina, called the fovea.

06:26 And so that's actually something you can see even though those cells are really small with the proper equipment on a physical exam.

06:34 You can actually examine the retina.

06:37 And it's one of the few places you can actually directly visualize things like essentially nerves.

06:43 And even blood vessels by directly looking through the pupil to the back of the eyeball to see the retina.

06:50 So when you were to look at a retina during a typical examination, you'd see a very bright area, that would be the optic cup.

07:00 And then this surrounding brighter area called the optic disc around it.

07:06 And that's the area where the optic nerve is going to be connecting.

07:11 But just more sort of centrally located, then that optic nerve is the fovea.

07:17 So when you look straight back into the retina, the somewhat dark area, a little bit aways from the optic disc is going to be the fovea.

07:26 And that's where again, those cones are going to be highly concentrated.

07:31 You can also see a lot of tiny little blood vessels here.

07:35 And so these tiny blood vessels, tiny branches of artery, we call those arterioles.