Optic Components of the Eyeball - Video Tutorials & Practice Problems

Optic Components

As light enters the eye and travels back to the retina. We said that the vascular layer or the iris is controlling how much light gets into the eye. But of course, needs to pass through the middle of the eye to make it back to the retina. And what it's passing through, we are gonna call the optic components. So remember we're saying the optic components of the eye are there to transmit and importantly, in the case of the lens to focus the light as it travels through the eye. Now, before we go through the different parts we're gonna talk about here, let's orient ourselves to our image. We have this transverse section of an eyeball here, this top down view of the eye and it's the right eye. And you can see here, we have three different structures color coded in these different shades of pink or purple in the front. Here, filling up the front of the eye. We have the aqueous humor in that sort of purplish color. We have this light pink disk shape here that's going to be the lens and then in the back filling up the back of the eye we have this brighter pink, that's gonna be the vitreous humor or sometimes called the vitreous body. All right. So let's start with the aqueous humor. The aqueous humor fills up the anterior, the star fancy word for front. So the anterior or front portion of the eye and you can see that here, this aqueous humor is here in between this purple color, between the iris and the cornea and also sort of surrounding the lens there as well. This aqueous humor is gonna be a liquid and it's gonna be made by the ciliary body. So remember when we talked about the ciliary bodies, we had these ciliary processes on the back here and that produced this aqueous humor and this aqueous humor very slowly sort of flows out, comes out through the pupil there and then it leaves the eye down here, sort of at the edges of the cornea there. And so when I say that it flows, it moves very slowly. It's not like actually flowing, but you can think it's always sort of being replenished. It's always sort of making a little bit more and it's draining out from the sides. Now, the job of this other than just letting light to pass through and to fill up the eye is to nourish the lens and the cornea. So the lens and the cornea both have living cells in them, but they're both avascular, there's no blood vessels there because you need to see through them. So those cells that are living there need to get their oxygen and nutrients from somewhere they get it from this aqueous humor. Now, aqueous humor doesn't have a lot of oxygen or nutrients in it. It's not, you know, nowhere near what blood does but those cells aren't that metabolically active. So it has enough to keep them alive and enough to help, let them do the jobs they need to do. All right. So as the light moves through the aqueous humor, it's then going to hit the lens, the lens is this transparent flexible disk. So this round disc shape here and its real job is to focus the light as it comes in. So light needs to be focused. So it makes a really clear picture as it moves back and hits the retina. Now, we're gonna talk a lot about how the lens focuses light in a future video coming up right now. We just wanna figure out what its structure is. We are gonna say that it is a vascular and so it doesn't have any blood vessels again because you need to see through it. You want it to be really clear and it's gonna be made up of two layers. First, we have the lens epithelium, this is made of a layer of cuboidal cells. So you have a layer of cuboidal cells on the outside and the inside is gonna be these lens fibers made of crystalline and you can just remember that term crystalline protein because crystalline, well, it makes sort of this crystal like structure that light can pass through and be focused. All right, as light passes through that lens, it then has to travel back to the retina and to do that, it's gonna travel through this vitreous humor or sometimes called the vitreous body. This is gonna fill the posterior, the star sort of fancy word for back there. So the whole back portion of the eye is gonna be filled with this vitreous humor. And unlike the aqueous humor, this vitreous humor is a gel. And so remember the vitreous humor is a liquid. So it's always being replaced, some is always draining out of the eye and new liquid is being produced. Well, this aqueous humor, I'm sorry, this vitreous humor is a gel. So this is actually made once during fetal development and then you get the same vitreous humor for your entire life. Now there's a lot of liquid in it. So there's liquid that diffuses in and out. But the gel substance, the stuff that makes it a gel is just made in field development and you get it once, all right, its job other than just, you know, letting light pass through is to really fill up that eye and maintain eye shape. And I sort of describe the eye kind of like an inflated soccer ball. It's this vitreous humor and also that aqueous humor that's inflating the ball. Ok. So that's all we're gonna talk about. The aqueous and the vitreous humor. We are gonna talk about the lens in more detail in terms of how it focuses light. We'll do that coming up. But of course, first we have example of practice problems. We'll see you there.

Optic Components of the Eyeball Example 1

All right, everybody. Let's take a look at this example here together, it says that glaucoma is a condition where the optic nerve is damaged due to increased internal pressure in the eye, increased pressure inside the eye pushes on the retina, causing the tissue to die and vision to become patchy. One cause of glaucoma is a build up of excess fluid in the eye based on their properties, which fluid of the optic components is more likely to build up. All right. So remember the retina is running all the way around the back of the eye here and we have the optic nerve here. And so to answer this question, the first thing I wanna do is label my optic components. So first off, we have the vitreous humor and remember the vitreous humor shown here in pink is this clear gel like substance that's really filling up the majority of the eyeball. Remember the eye I described sort of as this inflated soccer ball and this vitreous humor is doing a lot of that inflation filling it up. Now, as I look at this, I see the vitreous humor is right up against the retina and the optic nerve there. So I'm kind of tempted to say that's gonna be my answer because if something's pushing on the retina, the thing that is pushing on it has to be the vitreous humor. But before I say that's my answer. Let's see, what else we got. We also have here the lens. Now, the lens is this, you know, hard but flexible structure. It's not a fluid, it's not gonna be that. And then we have the aqueous humor and the aqueous humor was this liquid that's produced in the, and it fills up the front of the eye. And we said that it was produced, uh, you know, sort of back here in the ciliary processes and then it flows forward very slowly and actually drains out of these sinuses here in the eye. So as I look at this all together, well, yes, that vitreous humor has to be a thing that's actually exerting the pressure. If you remember, we said the vitreous humor is a gel and it's produced during fetal development and it just stays there your entire life. So it doesn't seem likely that you're gonna be getting more vitreous humor. We said that doesn't really happen. What could you get more of or too much of? Well, you could get too much aqueous humor because this aqueous humor is always being produced and sort of very slowly flowing forward and draining out of the sinuses there. And in fact, in a practice problem. Previously, we talked about what might happen if these sinuses get blocked and that could increase pressure in the eye. Yes. The thing exerting the pressure actually pushing on the retina back here will be the vitreous humor. But the reason it's gonna do that is that you're getting too much aqueous humor up here in the front. All right. So, therefore, I feel very good saying that my answer is the aqueous. Yeah. All right. Practice problems. All we'll see you there.

Cataracts are caused by changes to the crystallin proteins in the eye. Based on this information, what structure would you expect to be directly affected by cataracts?

• A. Aqueous humor.
• B. Lens.
• C. Vitreous humor.
• D. Both A and C are correct.