Alright, folks. Our example tells us that the table below lists 3 parts of the vascular layer. Then I want to know how does each component help regulate or control the light coming into the eye? And the three structures we're talking about here are the iris, the choroid, and the ciliary body. Now before we answer that, let's look at our diagram here. This is our transverse section or our top-down view of this right eye, and you can see that we have the vascular layer color-coded here.
So let's start with our first structure, the iris. Do you remember what the iris is and how it controls or regulates light coming into the eye? Now the first thing I'm going to do is I'm going to find the iris on my diagram here, and that's that brown structure in the front. The iris is that circular colored part of the eye in the front. And what it's doing, right, the iris is this circular structure that has a hole in the middle, and that hole is the pupil. And the pupil is the only way that light can get into the eye. So what the iris does, I'm going to say, is it controls the size of the pupil, and thereby it controls the total amount of light entering the eye. If that iris opens up, the pupil is bigger, more light gets in, the iris closes down, the pupil is smaller, less light gets in.
Next up, we have the choroid. Do you remember the role of the choroid in terms of regulating or controlling light in the eye? Well in my diagram here the choroid is this part all the way around the back. It's between the sclera and the retina. It is the vascular layer. And so as light comes into the eye, right, light is going to come in through the pupil, it's going to go through the lens, and then what you want is it to be absorbed by the retina so that you can see it. But not all light will be absorbed by the retina, and what you don't want happening is light hitting the back of the eye and then bouncing off and hitting other parts of the retina. That's going to create problems with your vision. What you want to have happen is light enter the eye, get picked up by the retina, but if it isn't picked up by the retina, hit the choroid and stop. So we said that the choroid has pigmented cells in it, and those pigmented cells are going to absorb excess light.
Remember the choroid also has the role of having a lot of blood supply in it, right? So this is the vascular layer and that's really where most of that vascularization is, is in the choroid and it is providing blood to the back half of the retina. So that's another really important job for the choroid. But in terms of controlling light, it's there to absorb excess light in the eye, so light doesn't bounce around and reflect.
Finally, we have the ciliary body. Remember the job of the ciliary body? Well, in our diagram here, the ciliary body's here in this sort of orangish-red color, and importantly, we have the ciliary muscles here, and then we have the ciliary zonules or the suspensory ligaments, sometimes called, and those are suspending the lens. So together, those work to control the shape of the lens. Right? So light is going to come in and you want that light focused by the lens so it creates a really clear image on the retina. The job of changing the shape of the lens so that it can focus is the ciliary body, the ciliary muscles, and the ciliary zonules.
Now we'll talk about how the lens works in more detail coming up. Right now, you just want to understand that the ciliary body has that role. Okay. So the vascular layer, remember vascular means blood supply, so it does provide blood to the eye. But you want to also remember that it has its job of controlling and regulating the light. Alright. With that, there are practice problems to follow. See you there.