[MUSIC] Okay, so let's look at how optical information comes into the eye and is altered as it goes through the various parts of the eye. And optical information is coming from the outside, it has to go through the cornea. It has to go through a fluid-filled chamber here, it has to go through the lens, and then another fluid filled chamber here called, where there's something called vitreous humor. And finally, we have to get to this retina. What's, what's the problem? Well, the problem is that if we didn't do anything. The world would look like that. This is a, a view of a bicycle that's under a couple of feet of water. And the refractive index of the water and the refractive index of air are very, very different and it makes everything very like that [LAUGH] so, what we, in, in air the refractive index is one. It's, it's it's theori, or, it's very close to one. Not different from theoretical vacuum. But the cornea has a refractive index that's like water and the lens has a refractive index that is like glass, similar to that of glass. And what these refractive index does, does, is it determines the, the bending of the, of the light rays. This one, what we found out, was this one has a, the cornea has a refractive index that's like water. This fluid is very watery. This has a refractive index that is like glass. And this fluid, it has a refractive index that's like glass. And what this does is it takes this and it bends it, and it's every, all the light rays are being bent in exactly the same way. So if there's an arc that looks like that, it's going to look like that on the retina. Instead of, as we saw with the bicycle, where some something like that, look like that, okay? We're going to match the refractive index of the materials so that we can actually see things on more accurately. So the way, most of the refractive index matching happens when light actually hits the cornea. The cornea is doing the big, big job. It's, it's akin to the focus on a microscope. The, the coarse focus, or the coarse focus on a pair of binoculars. Whereas, the lens is akin to the fine focus, just making it just perfect. But most of what happens is done by the cornea, if the cornea doesn't do it's job things are going to, not going to look crisp, and then the lens is fine tuning that, okay. So, what we're going to do in, in what this whole scenario is built for looking at far objects. Objects that are say, 20 to 25 feet or 7 to 8 meters away. We use a different system to look at near objects. If we looked at near objects we, the way that we look at far objects, they would not appear crisp and and detailed. So in the next segment, we're going to look at what happens when we look at near objects during near vision. [MUSIC]