Inner Layer of the Eyeball: Study with Video Lessons, Practice Problems & Examples

The retina, crucial for vision, contains photoreceptors: rods and cones. Rods, sensitive to low light, enable grayscale vision, while cones, concentrated in the macula lutea and fovea centralis, provide color vision and high acuity. The optic disc creates a blind spot as it lacks photoreceptors. Light passes through retinal wiring before reaching photoreceptors, illustrating an evolutionary design. Understanding these structures and their functions is essential for grasping how the eye processes visual information.

Inner Layer

As we continue to follow the pathway of light through the eye, we've now reached the inner layer, and this is where we have the photoreceptors. So this is where light gets absorbed, and we start to send an image to the brain. Alright. So remember, the inner layer is also known as the retina, and you're going to see it called the retina far more than you'll ever see it called the inner layer. And the retina functions for what we're going to call phototransduction, and phototransduction just means the conversion of light energy into an electrochemical response. And by electrochemical response, I mean a nervous signal. So light comes in the eye, what goes out to the brain, an electrochemical response or a nervous signal. Alright. We're going to say that there are 2 major layers of the retina that we're going to talk about. And when we do this, we want to first just look at our diagrams here. Over here, we have this cross section, this transverse section of the right eye. And you can see here in yellow, we have the retina, and the retina is really covering the majority of the back of that eyeball there. And then those neurons from the retina actually go out and they become the optic nerve. Now zoomed in here, we've taken a section sort of about right here and we'll pull that out. That would be what we're looking at here. So this is a section of the retina, and you can see color coded we have all the different cells that we're going to talk about. And when you're looking at this, the back of the eye is back here and light is coming in in this direction. Alright. So our 2 layers. Our first layer that we're going to talk about is the pigmented layer. And this is a single cell layer at the back of the retina, and it is going to support and protect those photoreceptors, And it's also going to absorb excess light. So as we look at our diagram here, that's these cells all back here. A single cell layer sort of dividing the end of the retina from what's behind it, which, remember, that is the choroid. So I'll just write that in here, the choroid. And it's also supporting those photoreceptors. Right? Remember, all the blood supply for the back half of the retina is in this vascular layer in the choroid, So that blood supply or the nutrients from that blood supply actually has to come up through this pigmented layer. It's also going to do other things like, absorbing excess light. That's another job of the choroid as well. Alright. That pigmented layer, extremely important to make sure that those photoreceptors work and for functioning of the eye. In terms of understanding how the eye perceives light though, not that important. We're not really going to talk about the pigmented layer really much at all anymore. We're now moving on to the neural layer, and we're going to spend a lot of time going forward talking about what's going on in this neural layer. In the neural layer you have the photoreceptors and the neurons. Alright. Photoreceptors absorbing the light, the neurons passing that information on so that you can perceive it into the brain. Alright. So first up, we'll look at the photoreceptors. And the photoreceptors, we have 2 types. We have the rods and the cones, and we'll go into how these are different from each other coming up later on. And these rods and cones are going to be excited by different wavelengths of light. Right? So remember, light is coming in this way, and then all the way in the back of the retina, we have here in orange. Those are those rods. And then we also have in red a few cones drawn in as well. So those absorb the light and that's where that phototransduction happens. It's going to convert it into this electrochemical signal, this nervous signal, and then it's going to pass that signal back up through the retina in this direction. The first place that signal goes is into this layer of pink cells that we see here. Those pink cells are what we're going to call the bipolar cells. The job of the bipolar cells is to connect those photoreceptors and pass the signal from the photoreceptors to the ganglion cells. And the ganglion cells are these cells in blue here in the front of the retina. So bipolar cells get that message from the photoreceptors, pass it on to the ganglion cells. The ganglion cells then generate the action potential. So in the photoreceptors back here and in the bipolar cells here, so far we've just had graded potentials. Once it reaches the ganglion cells, we start an action potential because the ganglion cells have these really long axons that travel along the retina and then travel out through the optic nerve to the brain carrying that signal to the brain. So we're going to say they generate an action potential and from there run along the retina and form the optic nerve. Alright. So again, light comes in this way. The(signal is sent back out this way from the photoreceptors to the bipolar cells, to the ganglion cells, along the retina, and then it can come out the eye through the optic nerve. Now you'll notice we have 2 other cell types here. In green, we have amacrine cells, and in blue, we have horizontal cells. You can see these amacrine cells here, and we have one horizontal cell down here. It's very unlikely that you need to know the details of what these cells are doing, but you should probably know that they are in there. These cells aren't really in the direct pathway of this electrochemical signal of this nervous response. They're sort of going horizontally or sort of across the retina and doing sort of crosstalk between the different cells. And what they're really doing is sort of that first, first pass of visual processing, kind of turning up and turning down and modulating some of the signal based on what's happening in the retina. So some of the initial visual processing actually happens in the eye before it leaves, and that's what those cells are doing. But, again, it's really unlikely that you need to know the details of that. Just know that they're in there and they're sort of doing crosstalk between the cells. Alright. So those are the structures that we need to know about, but before we go on, I just want to note that we have light coming into the eye. I've said this a few times. The light comes in the eye this way, the receptors are all the way in the back, and then it sends a signal back out this way. So the light has to actually sort of pass through what I often refer to as kind of the wiring of the retina, those bipolar cells and the ganglion cells. That kind of feels like the backwards way to do it. Right? If I were to design an eye, I would probably put the photoreceptors as the first thing the light hits. And so a lot of people wonder why that is, and no one really knows, but a lot of the consensus is that it's just kind of an accident of evolution. In our ancient ancestors, this was the developmental process that got set up and now this is just how the eye is built. And if you were to really design an eye, maybe you would build it the other way. Some eyes are built that way. The octopus eye, which evolved completely separately from the human eye, but works very similarly, It has actually those photoreceptors in the front and the wiring behind. The way I kind of think of our eye is if you imagine like a flat screen TV, and you think of, like, where the picture is on the TV, I'd liken that to the photoreceptors. Well, in the back of a TV, you'd have to have all this wiring connecting all those things. Now I don't actually know how a flat screen TV works, but just go along with me for this example. The way the Retina is built, you kind of put all the wiring in the front of the TV and you have to look through it to see the picture, so you just kind of try and make it clear and minimize it as much as possible. Again, it kind of feels like the backwards way to do it. Remember, our eye is a marvel of biological engineering. It doesn't mean though that it's perfect. It works really, really, really well. That's good enough. Alright. Again, we're going to talk about a lot of what's going on in this neural layer a lot more going forward. We'll see you there.

Inner Layer of the Eyeball Example 1

Alright. Our example tells us that the following list contains many of the structures that light must pass through to reach the rods and the cones. Remember, rods and the cones are our receptor cells in the retina. And we need to place the structures in the order that light would pass through them. Alright. So here we have light coming at your face. It has to go through all these things until it reaches the rods and the cones in the retina, where we can actually start a nerve impulse and tell our brain that we saw something. So as light is traveling towards you, what's the first part of the eye that it's going to hit? Well, I see right here, the cornea. The cornea is that clear part of the fibrous layer, that outer layer of your eye right in front that light first passes through. So I'm going to start by putting down a C for the cornea. What's it going to go through after it goes through the cornea? Well, what's right behind the cornea? Right behind the cornea is a little bit of space, and that space is filled with the aqueous humor. The light goes through the cornea into the aqueous humor, that clear liquid, so I'm going to put down A. It passes through the aqueous humor. What's right behind there? Behind there, the next major structure is going to be the lens. Right? The light is going to pass through the lens. There, it's going to get focused. But first, I'll just put down an L here for the lens. It passes through the lens and now it has to travel through, well, the majority of the eyeball to make it back to that retina. So what is it going through as it travels from the lens to the retina? It's traveling through the vitreous humor. The vitreous humor, remember, is that gel-like substance that's really filling up the majority of the eyeball. So I'm going to put down V for the vitreous humor there. And then it's going to hit the retina. Alright? We have this neural layer of the retina, but we have a couple of layers of cells that it needs to go through before it reaches the rods and cones. So, do you remember which layer of cells is sort of in the front of the retina there that light's going to hit first? No. First, it's going to hit the ganglion cells. So I'm going to put down G. Remember, ganglion cells are the cells that have really long axons that run down the retina and then down the optic nerve, sending that impulse to the brain. Alright. It passes through the ganglion cells. The next layer it has to go through, well, we only have one more option here, but it's got to go through the bipolar cells before it reaches the rods and cones. So, I'm going to put down B for bipolar cells there. Remember, the bipolar cells connect the impulse from the rods and cones and pass it on to the ganglion cells. Now this light finally hits the rods and cones. We can start our nerve impulse. We can tell the brain we saw something. It's going to send that nerve impulse to the bipolar cells. The bipolar cells are going to pass it on to the ganglion cells. It's going to send a message down those axons, down your optic nerve, to your brain, and you will see something beautiful. Or maybe ugly, depending on what you're looking at.

True or False: if false, choose the answer that corrects the statement.

Waves of light must pass through both the ganglion and pigmented cells before reaching the photoreceptors.

• A. True.
• B. False, light reaches the photoreceptors first.
• C. False, light must pass through the ganglion cells, but not the pigmented cells.
• D. False, light must pass through the pigmented cells, but not the ganglion cells.

Once light is absorbed, what is the path of the nervous signal?

• A. Rod or Cone → Bipolar Cell → Ganglion Cells.
• B. Rod → Cone → Horizontal Cell → Ganglion Cell → Bipolar Cell.
• C. Rods → Cones → Horizontal Cell → Amacrine Cells → Bipolar Cell → Ganglion Cells.
• D. Pigmented Layer → Rod or Cone → Bipolar Cell → Ganglion Cells.

Which part of the neural layer continues into and becomes the optic nerve?

• A. Rods.
• B. Cones.
• C. Bipolar Cells.
• D. Ganglion Cells.

Comparing Rods and Cones

As we talked about the structure of the retina, as we said that there were 2 types of photoreceptor cells, our rods and our cones. Here we want to figure out what the difference between those two things are. Now we're going to talk about rods and cones a fair amount going forward and really sort of dive into how they work. Here, we just sort of want to look in sort of grand schemes, what's the difference between these two things. So we're just going to start out saying that there are 2 types of photoreceptors in the retina, and they are going to be named for their shape. And so we can look over here at our image, and this is sort of just pulled out from that image that we had before of the retina. We can see here we have the axons and then the ganglion cells. We have the bipolar cells, and then this is what we're really talking about here, the rods and the cones. And just remember, light is coming in this way to the eye. So you can see in orange here, these are the rods, and you can see that they are sort of long and skinny, but sort of the same thickness the entire way through. Where in contrast, our cone, here in red, has a sort of pointed cone-shaped end on it. So that's where those names come from. Alright. What's actually different between them and how they function, though?

Well, rods and cones, the first difference and probably the key difference that people are aware of is their ability to see color. Rods can only see in grayscale. Rods are going to be really good at sensing the brightness of things, but they cannot distinguish different colors. So if you're using only rod vision, your vision is in black and white. Now, in contrast, cones. Cones provide color vision. Now, we normally think of seeing the world in color, so when you think of color vision, you're really thinking of your cone vision. Alright. Well, I like to see in color, so why do I have rods? Well, a key difference here that makes rods very useful is that rods have really high sensitivity. And by that, they mean that they work in very low light. Now in contrast, cones have low sensitivity. They require relatively bright light to sense anything. Now in today's world, we don't experience our raw vision nearly as much as probably our ancestors did because, well, it's bright everywhere. If it's dark in a room, I just turn on a light and make it bright, and heck, everything's in color. But if you've ever spent some time in a dark place or walking around at night, you'll know that you can actually see things pretty well even in very dim light, but you can't see color very well in that dim light. If you're walking around at night again, you can see well, but you can't see color that's because you're really experiencing your rod vision. The light is low enough that those rods are being stimulated, but the cones are not. And in fact, in bright light, your rods largely shut down. So your rods during the daytime in bright light really aren't doing much at all. Really, you're pretty much only using your cones when it's bright up. Alright. Our next difference is going to be acuity. And by acuity, we just mean how fine or how detailed is that image that they can see? Well, this comes down to the fact that rods have this many to 1 ganglion relationship. So by that we mean, as we look over here, we have 3 different rods, and they're all sort of funneling up and connected to the same ganglion cell up here. In reality, there's going to be dozens of rod cells that connect to every ganglion cell. So that means that when this ganglion cell is stimulated and it sends an action potential down its axon, down the optic nerve to the brain, the brain will know where in the retina it came from, but it can't map it back down to the individual cell. It just knows that this ganglion cell was stimulated. It doesn't know which rod that it connects to actually did the stimulation. So this means that rods see with low acuity. They sort of see in low definition. You can sort of think of it as kind of like a big pixel size, because all of these rods are funneling in. It's sort of covering a decently large area of the retina, at least relatively large area of the retina connected to a single ganglion cell. So that's sort of like a big pixel you're seeing with. Now one of the reasons it does that is that helps with that sensitivity. Now a single rod might not be stimulated enough to set off this action potential in a ganglion cell, but if many rods are stimulated just a little bit, that might be enough to get this ganglion cell over that threshold and send a signal 1 to 1 ganglion relationship, and that allows us to see with our cones in very high acuity. So we look over here, we have this cone right here, and we can see this, like every cone, connects to a single bipolar cell, which connects to a single ganglion cell, which then sends the signal to the brain, and the brain can map that back to the single cell that was stimulated, the exact place in the retina. That means that with your cone vision, you can see in really high definition. Alright. Location. These are not distributed equally in the retina. In fact, the rods are going to be concentrated in the periphery. So your peripheral vision, the sides of your vision, is largely rod vision. You do have cones out there, but that's where most of the rods are. That means that in your peripheral vision, well, you have low acuity. Right? It's tough to see detail in your peripheral vision, but you do have high sensitivity, and this kind of makes sense. You want to see things that are moving or flying at you or, I don't know, a tiger jumping out of the bushes out of your peripheral vision. Your rods will be able to see that, but th

Inner Layer of the Eyeball Example 2

Alright. Our example says that while walking through the woods at night, you realize that you can see things better if you don't look directly at them. In a single sentence, why might that be? And the table is provided as a reference. Alright. So this table cues us into what our answer is going to be about, our rods and our cones. As we go through this table, well, we have many rods and we have few cones. That's not going to be related to this. The rods are in the periphery. Our cones are in our center of vision. Alright. That seems like it's going to be part of our answer. Right? So in our peripheral vision, you have more rods, and, in fact, you have no rods in the center of your vision. Most of your cones are in the center of your vision. But, here, we're saying you're going to see things better at night if you actually look just to the side of them, if you use that peripheral vision. Alright. So that's going to be part of my answer, I'm almost certain, as I go down. I see here that rods function best in low light, and cones, remember, require very bright light. So if I put these two things together, I get my answer. If I'm walking through the woods at night, it's low light, I need to use my rod vision, but I have no rods in the absolute center of my vision. So if I want to see something really clearly, I actually can't look directly at it. I have to look just to the side of it, so that that light is hitting just to my peripheral vision where my rods are. In bright light, right, you have enough light, it can stimulate the cones, you want to look right at something. Okay. So with that, I'm going to write my answer. I'm going to say that rods see in low light but are located in the periphery. They're located in your peripheral vision, And this is true. You're walking at night. It's easier to see things if you're using your rod vision, that grayscale vision, if you don't look directly at something. So now you know if you're ever going on a night hike and you trip on a stick and you say, what the heck? I was looking right there. Why didn't I see it? Maybe you shouldn't have been looking right there. You want to look just to the side.

Which of the following statements is true for cones.

• A. There are more cones than rods in the retina.
• B. They are specialized for low light vision.
• C. They are concentrated in the center of the retina (fovea centralis).
• D. They are named for their long cylindrical shape.

Different animal species differ in the relative number of rods and cones that are present in their eyes. Which of the following statements would you expect to be true about these differences?

• A. Species that require greater visual acuity will have relatively more rods in their eyes; species that require greater peripheral vision will have more cones.
• B. Nocturnal (active at night) species will have relatively more rods in their eyes; diurnal (active in the day) species will have relatively more cones.
• C. Species that require better depth perception will have relatively more cones in their eyes; species that require greater field of vision will have more rods.
• D. Nocturnal (active at night) species will have relatively more cones in their eyes; diurnal (active in the day) species will have relatively more rods.

Structures of the Retina

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.

Inner Layer of the Eyeball Example 3

Alright. We said if you've never found your blind spot before, we're going to do it together, so let's give it a try. It says here to close or cover your left eye, and then you want to look at this x with your right eye. And keeping that black spot sort of perfectly horizontal to the outside of your vision, you want to move your face or move the screen closer or farther away from it until that black dot just disappears. Now if I'm to do this on my phone I got my phone right here. I'm looking. So I move it forward and back. It's right about there that it disappears for me. That black spot has just sort of blinked out, and that's about oh, what is that? That's like a foot from my face, something like that. If you're doing it on a computer screen, right, it's going to be bigger, so it's going to be farther away from you, maybe up to a few feet, depending on the size of the screen. Now when I've done this with students before, there's always someone who says that it doesn't work for them. Yes. It does. Everybody has a blind spot. If it doesn't work for you, just make sure you're covering that left eye. You're looking at the x. Make sure that black spot is on the outside of your vision because your blind spot is on the inside side or the sort of the nose side of your retina, and just move it back and forth slowly. Eventually, that blind spot should just sort of blink out, and you won't even know it's there anymore. Alright. Now we have here, just to remind ourselves, why do you have a blind spot? Well, what's the structure that's there? Well, remember, we said the structure is the optic disc, and the optic disc is where the optic nerve enters or leaves the retina, depending on your perspective. And because it has to come in, and remember all that wiring sort of on the inside of the retina and has to get out of the eye, it ends up that you have no photoreceptors, no rods or cones at that optic disc. Alright. Pretty amazing. Again, you often don't know it's there because your other eye just sort of fills in the picture for it. Or if you're just looking with one eye, your brain just kind of imagines what should be there. So I always think this is fascinating too, though. In just sort of the amazing structure, this amazing product of evolution, this engineering design of the eye, this feels like something it got wrong. Our bodies are pretty good. They're not perfect.

Inner Layer of the Eyeball Example 4

Alright, folks. Let's look at this example together. It says that the graph below shows the density of rods and cones in the retina relative to their distance from the center of vision in angular degrees. One type of receptor, either rods or cones, is represented by the red line. One type, either rods or cones, is represented by the black line. And then, based upon what we know about rods and cones in the retina, we need to, a, label a line for cones, b, label a line for rods, c, identify and label the structure between 15 and 20 degrees, marked by the dotted lines, and then, d, circle the area that represents the foveas and trellis. Alright. So before we do all that, let's look at our graph here. We have on the x-axis angle from the center of the retina in degrees, and we have the center of the retina here. That's the zero point, and then we go out in both directions for our peripheral vision. So remember, the retina is on the eye, which is basically a sphere, so we can measure it in angular degrees as sort of like how far along it is in that circle of the eye. And then on our y-axis here, we have receptors per millimeter squared, so how densely packed are the receptors from 40,000 up to 160,000? Alright. That's a lot of receptors per millimeter squared, by the way, but let's keep going. Okay. So first thing we want to do is label the lines. So let's look at the lines. First, we have this black line, which way out in the peripheral vision. Right? This is our peripheral vision here. It's present there. Right? It's less common than it's going to be, but it keeps on getting more and more common until the close peripheral vision. It's very common. And then in the center of vision, something crazy happens. It dives down. There's nothing there. And the same thing on the other side. Right? Way out in the peripheral vision, not much, more and more common until the close peripheral vision. Something happens kinda weird right here that we'll deal within a second, then it dies down. Nothing at the center of vision. The red line, kind of the opposite. It's rare, but it's there in all the peripheral vision. And then at the center of vision, wham. There's tons of them. And then it dies right back down again. And in that peripheral vision again, rare but there. Alright. So which line do you think represents the cones? Well, that's going to be the red line. Cones, remember, are most prevalent in the center of your vision. And in the absolute center of vision, you actually have only cones. So that's that one, and that means that the black line must be rods. And that makes sense. Rods are most common in your peripheral vision and actually in that very center of your vision. There aren't any. Okay. Next, we need to identify and label the structure between 15 and 20 degrees marked by the dotted line. So here's this marked by the dotted lines right there, And as we look here, what we see happening is these lines just stop, and then they start up again. It's like there's just no rods or cones there. So what's the structure just a little bit off into your peripheral vision that has no rods or cones? That I'm going to label as the optic disc or your blind spot. So remember, the optic nerve needs to get into the eye or out of the eye, depending on your perspective, because all the neurons are on the inside of the retina. Where they pass through the retina, there are no photoreceptors, and we can see that in this graph here. Alright. Finally, we want to circle the area that represents the fovea centralis. Alright. Well, remember, the fovea centralis, well, that word centralis, it's right there in the absolute center of the vision where you have only cones and no rods. So that's right here at 0 degrees. Alright. So that's the fovea centralis right there, or I guess you probably could circle the tip of the line too. I'm not sure. Same thing. Alright. At 0 degrees, the center of your vision, only cones, no rods, your foveas and trellis. Alright. This is a fairly common graph that you may see, but just being able to break it down and understanding where all these things will give you a really good idea as to how these rods and cones are distributed in the eye and how that affects your vision. For that, see you in the next video.

On the image of the retina below, identify the structures located in each circle.

• A. Structure 1 is the optic disc, structure 2 is the macula lutea.
• B. Structure 1 is the fovea centralis, structure 2 is the macula lutea.
• C. Structure 1 is the optic disc, structure 2 is the fovea centralis.
• D. Structure 1 is the macula lutea, structue 2 is the optic disc.

Here’s what students ask on this topic:

What is the function of the retina in the eye?

The retina, also known as the inner layer of the eye, is crucial for vision. It contains photoreceptors—rods and cones—that absorb light and convert it into electrochemical signals. This process, called phototransduction, allows the retina to send visual information to the brain via the optic nerve. Rods are sensitive to low light and enable grayscale vision, while cones provide color vision and high visual acuity. The retina's structure and function are essential for processing visual information and enabling sight.

What are the differences between rods and cones in the retina?

Rods and cones are the two types of photoreceptors in the retina. Rods are highly sensitive to low light and enable grayscale vision, making them essential for night vision. They have low visual acuity and are concentrated in the peripheral retina. Cones, on the other hand, provide color vision and high visual acuity. They require bright light to function and are concentrated in the macula lutea and fovea centralis, the center of the retina. This distribution allows for detailed and color-rich central vision.

What is the macula lutea and its significance in vision?

The macula lutea is a small, yellowish area in the center of the retina, responsible for central vision. It contains a high concentration of cones, which provide color vision and high visual acuity. At the center of the macula lutea is the fovea centralis, which contains only cones and offers the highest visual acuity. This area is crucial for tasks requiring detailed vision, such as reading and recognizing faces. The macula lutea's specialized structure allows for sharp and detailed central vision.

Why does the optic disc create a blind spot in vision?

The optic disc is the point on the retina where the optic nerve and blood vessels exit the eye. This area lacks photoreceptors, creating a blind spot in the visual field. Despite this, most people are unaware of their blind spot because the brain fills in the missing information using data from the other eye and surrounding visual cues. The blind spot is located in an area of lower visual acuity, making it less noticeable in everyday vision.

How does light travel through the retina to create a visual signal?

Light enters the eye and passes through the retinal layers, including the ganglion and bipolar cells, before reaching the photoreceptors (rods and cones) at the back of the retina. The photoreceptors absorb the light and convert it into electrochemical signals through phototransduction. These signals are then transmitted to the bipolar cells, which pass them to the ganglion cells. The ganglion cells generate action potentials that travel along their axons, forming the optic nerve, which carries the visual information to the brain for processing.