 Now we use prisms to bend lights. Now I'm gonna take you back to that time in middle school when you learned about prisms. When light hits a prism, there are two things that happen. One, it bends light, and two, it moves an image. Right now we're gonna focus on a light bending part. Every prism has two components, an apex and a base. The base is kind of that thicker part. So what happens is that light will travel to the prism and light always bends towards the base. This is a law. The light will always bend towards the base. So remember that as we're going through this. Now if we take these two prisms and we place them base to base and apex to apex, and now I have two prisms that we're going to work with, if we do that, what's gonna happen here? So we've got on the image on the left, we've got the bases together. And on the image on the right, we've got the bases on the outside. And the light always bends in which direction? The light will always bend towards the base. And so you'll see that in the first image the light will actually come together. And in the second image, the light will spread apart. We call this converging and diverging. What do these two things kind of resemble? If you remember from the illustration I gave you a little earlier, they look like this. A plus lens and a minus lens. So you'll notice that the plus lens has a thicker center and then the minus lens has a thicker edge. Same thing here with these two prisms. So this is the basic concept of the plus prescription and the minus prescription. We're bending the light and we're converging or diverging the light. The light will come in and hit the lens and it'll actually converge together. And then on the minus lens, it's going to hit the lens and it'll actually go apart and it'll spread. So it spreads light and brings light together. Where the two prisms meet, apex to apex, or base to base, that's what we call optical center. And so in the optical center, there's actually no deviation of light. It actually goes right through the lens. It doesn't spread or come together. It's just constant. So you'll learn a little bit later on in our measurements about why it's so important to take the optical center. Let's take this patient and remember with the plus lens, we're gonna converge light together. So we're gonna allow the light to come together. So what happens with this hyperrope is that when we put this lens in front of their eye, rather than the light focusing behind the retina, this will allow the light to come in through the lens and actually focus right on the retina where it's supposed to. Ta-da! That's the magic of optometry.