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OK. Um Hello everyone, my name's Darren and we're having the visual and auditory and vestibular systems talk here. So essentially, it's going to be three parts. We're going to have the visual system, the auditory system and then the vestibular system. So to kick off with, we are going to start with the visual system. So here we have the eye anatomy. We have the ciliary body, the iris pupil cornea lens, suspensory ligaments, the optic nerve blood vessels and the phobe. Now there's three layers to the eye. We have the sclera choroid and the retina. So the initial outer layer of the eye is called the conjunctiva, which is a thin transparent tissue co covering the outer surface. This covers the visible part of the eye and lines the inner eyelids. And it is also nourished by the tiny blood vessels. We then have the sclera, which is over here. As we can see, this is a white part of the eye. It's a hard opaque protective coat and that has a very high water content. Now, within the eye, we then also have the cornea which is a transparent dome shaped window at the front of the eye, we have the uvea which has three parts, it is made up of the iris, the ciliary body of the hair as well as the choroid. Now, the uvea is a vascular coat of the eye and the three different parts have different roles. So for instance, the iris, it controls the light levels which are entering the eye through the pupil. The choroid is the blood vessels and contains the blood vessels which supplies the back of the eye. And we also have the ciliary body over here. Now, essentially all of this, all of these areas are very intimately connected, which means that disease would affect all of these parts, not just one. Now, after that, we have the lens, as we can see over here, the lens accounts for a third of the eye's refractive power and is also needed for accommodation, which is something that will cover afterwards. Now, the structure of the lens is that it's an outer acellular capsule and inner layer is elongated cell fibers which are transparent and over as time goes on, we can have cataracts building up which causes the lens to become less transparent. Now, after the three coats, we have the sclera and then we've talked about the choroid. Now we're moving on to the retina. The retina is a thin layer of tissue which forms the innermost lining of the eye. It captures the light rays and sends them to the brain via the optic nerve, the optic nerve is then the what's responsible for transmitting that electrical impulse from the retina to the brain. It connects to the back of the eye near the macular. Now, the macular is the blind spot and it has no light sensitive cells at that point, the optic disc, as you may have heard is the visible portion of the optic nerve. Now, we have the macular over here. So the macular is the center of the retina and is temporal to the optic nerve. So we can see the optic disc and the optic nerve going off of it. And next to that is over here, we see the macula macular is highly sensitive and is responsible for central vision. Now, the fovea is the center of this macular and this is where there's the highest concentration of cones and the lowest concentration of rods. Now, just as a question, you can try this in your own time. Where does the effect of power of the eye come from? And it comes from two third comes from the cornea and a third from the lens. And as part two, we have which of the following is not part of the uvea. The sclera isn't part of the uvea. Now going on to vision, we have two different types of vision. We have central vision which is mediated by the cones and we have peripheral vision which is mediated by the rods. Now, the detailed vision is necessary during the day is also what we know as color vision or phototopical vision. Now, this is needed for reading and facial recognition. Now, we assess central vision as a medic as a clinician through the visual acuity assessment. This is also known as the um where you do an eye test, for instance, where you stand 6 m away and you read off the numbers of the letters. And so the loss of fibular vision means that you have poor visual acuity. Now, peripheral vision is mediated by the rods. And so this is needed to detect any shape, movement is needed for navigation as well as night vision or scotopic vision. And so we assessed the how good our peripheral vision is through the visual field assessment, which is something that you cover during your cranial nerve session and your cast sessions. Now the loss of peripheral vision is leads to the inability to navigate your surroundings. So you won't be able to see in any depth perception, then you and you may need a stick even though you have 2020 vision. Now let's look at the retina itself. The retina has three different layers, the outer layer over here, as we can see is made up of photoreceptors. These are the primary neurons, the middle layer is made up of bipolar cells. So they have endings on either side. And so these are the secondary neurons and what they do is they modulate the sensitivity. So the photoreceptors detect the stimulus, the bipolar cells, they modulate how sensitive it is. And they have the inner layer also known as the retinal ganglion cells or the tertiary neurons. And so what happens is all of these tertiary neurons or these ganglion cells, they come together. And that's what forms the optic nerve. The optic nerve is essentially made up of these ganglion cells. And this is what then transmits the signals from the photoreceptors and the bipolar cells to the brain. So now the photoreceptors, there are two different types of photoreceptors. We have rods and we have cones. The rods are the longer outer segment and they are 100 times more sensitive to light, which is what allows them to have night vision, but they have a very slow response time. So essentially, it takes us a long time to detect a change. Whereas with cones and there's 6 million of them, there's a lot less cones than rods and they are less sensitive to light. But however, this doesn't really matter because during day, there's a lot of light. So that's why this allows us to see in color. And we, and this allows for a foster response and the different cones are present for different colors. So, s cones are for blue M cones are green and L cones allow you to see red light. Now, the way you test for color blindness is through the Ishihara test, so essentially you might have seen these color pallet before, but you get people to try and see what number is inside. So you can see over here 7, 1316, 8, 12, 9. And if someone can't see these colors, then they have color blinders. Now, there are two different types. There's due to anomaly AK A or Daltonism, which is the most common type and this is when they can't see the color red. Whereas so essentially they won't be able to see the uh some of these colors of the hip. However, with achromatopsia, it's full color blindness. So they can't see any of these numbers, which is essentially known as full color blindness. Now, we have the different types of optics. So we have ametropia, which is essentially when the axial length matches the refractive power. So this is our normal vision. So, and if you have normal vision, 2020 vision, you have a metro, then we have ametropia, which is a mismatch between the axial length and the refractive power. So this is if you need to wear glasses, if your vision isn't quite exactly accurate, then you have ametropia. Now, within ametropia, we have many different kinds. The first kind is myopia or nearsightedness, which is what affects most of us. So we can see close by, but we can't see further away things. So within myopia, we have parallel light rays which converge anterior to the retina. So if you have a retina, we have the light rays coming in front of the retina instead of actually on the retina. And so there's two different reasons for this. The first reason can be because of axial myopia, which is when the eye essentially is just longer than it should be, or there's refractor myopia, which is when there's excessive refractor power. So the le so the light is being refracted more than it should. And so the symptoms of this is you have blurry distant vision, you tend to squint and when you squint that leads to headaches. And the way you treat this is by having diverging lenses or you can have, you can remove the physiological lenses to actually reduce your refractive power. So there are two different ways that you can fix this. Now, the next way is hyperopia, which is when there's farsightedness. So what happens is if we have our retina over here, the light rays would converge behind the retina. So it doesn't actually converge on the retina again. So the reason for this is axial hyperopia, which is when essentially the eye itself isn't as shorter than it should be. And we have refractive hyperopia, which is when the light isn't being refracted as