We now want to talk about some structures of the retina, but the structures we're going to talk about here are macroscopic. We're talking about sort of larger scale structures, and they exist because the distribution of photoreceptors and neurons in the retina, well, it's not all equally distributed, and that gives rise to these distinct structures. Alright. So before we talk about these structures, let's orient ourselves to our image here. We have this same transverse section of the right eye that we're looking at, this top-down view of a cross-section of the eye. But here, we've really zoomed in on just the back part of that eye, and you can see here in yellow, that's the retina, and here coming out, heading towards the brain, that's going to be the optic nerve. Alright. So the first structure we want to talk about is called the macula lutea, and you can see that we have brackets around this area right here, and that macula lutea is going to be this area that is at the center of the vision, and it is going to contain mostly cones. Right? Remember, we said cones are mostly at the center of your vision and rods are mostly on the periphery. So your macula, center of your vision, that's where you're going to find most of your cones. Now you can actually see the macula if you look at a retina. It looks sort of like a yellowish oval. Now, at the center of the macula, we are going to have the fovea centralis. This is the center of the macula, and it contains only cones. And we can see that here. We have this arrow pointing to this little dip that you see in the retina. That dip is the fovea centralis. So because it contains only cones, remember, cones have really high visual acuity, that means that at this point, you have your absolute highest visual acuity. Right? You can see things with the absolute most detail, and that makes sense. If you want to see things in a lot of detail, you look straight at it and that light hits the center of your retina. It hits the fovea centralis.
I noted though that you can see this little dip, and that little dip is the fovea centralis. So the reason there is a dip there is because you have all these internal retinal structures, like the axons from the ganglion cells, and all the different connections, so that the signals from those photoreceptors can make it to the brain. Well, we said light is coming in this way, and it's going to hit all that sort of wiring of the retina first before it makes it to the photoreceptors, which are actually on the back of the retina. Well, in this fovea centralis, the center of your vision, all those retinal structures, as much as possible, those axons and all those other cells, go around the fovea, and that creates that little pit. There isn't as much sort of wiring there because at the center of vision where you want the absolute clearest vision, you don't want all those axons and extra cells getting in the way of the light. So at the fovea, it's really just about the thickness of just the photoreceptors and as few other cells as possible. Okay. So that's the macula and the fovea centralis.
We're also going to talk about the optic disc. And the optic disc is going to be a sort of circular structure right here on the retina, and it is the location where the optic nerve and blood vessels leave the eye, or enter the eye depending on your perspective. Right? So remember, all this wiring's on the inside of the eye. So to get out of the eye, all of these axons running through, they need to get through the retina into the other side of the eye as part of the optic nerve somewhere, and so that happens at the optic disc. They come through the retina and head out to the brain. So that means that you have this area right here where there are no rods and cones. There's only those axons and also the blood vessels that are supplying the blood to the inside of the retina. Well, if you have no rods and cones in that optic disc, it means you can't see anything there. You have a blind spot. This creates a blind spot in your vision.
Now, if you've never looked for your blind spot before, you probably don't realize that you have it, and that's for two reasons. First off, one eye can see where the other eye's blind spot is, so your brain is able to fill in that picture with the data from the other eye. But even if you cover up one eye, you don't see, like, a black circle in your vision anywhere. That's because your brain kind of just imagines what it thinks should be in that blind spot. The blind spot's in an area of a little bit lower visual acuity, and so, you know, you're not seeing a ton of detail there anyways. Your brain just kind of fills in the colors around it, and you don't realize that you're missing anything. Alright. If you've never looked for your blind spot before, we're going to find it in an example coming up. I encourage you to do that with me. Otherwise, we have other examples and practice problems. I'll be there. I hope you will too.