[Music] all right so we're going to be looking at the eye the struct the different structures and function all right so let's start with our outer layer so there's a tough white outer layer called the cero and this has a protective function moving inwards we have what is called the choid and this is the layer that supplies nutrients to the blood vessels and it also prevents in it contains melanin and it prevents internal reflection in the eye our third layer this is the layer of interest because this is where we find our photo receptors the rods and cones there's also an area in the retina called the phobia mainly cones are seen here the most sensitive part of the retina all right so the second layer merges into what is called orary body orary muscles and theary body it's attached to these structures called ligaments so this is a connective tissue it connects the muscle to the lens and it accommodates meaning the muscle can contract to slatten the ligaments and let the lens bulge or can relax tightening the ligaments and then the lens will flatten we have a transparent lens it's by convex so it's more bulging or more of a con converging lens and it does fine adjustment to the light rays all right in front of the lens is our Iris which is a colored dis made up of muscles so we have circular muscles which will relax to widen the pupil and when they contract they narrow the pupil that's the circular muscles in the iris the radial ones are antagonistic so they work opposite to the circular so in dim light our circular Ones Will relax so in dim light the circular ones relax and the radial ones contract while in bright light the circular muscles will contract and the r ones relax in front of our iris is aquous humor so it's a colorless fluid and it helps to maintain the shape of the caria so this outer bulging part of the when the Scara reach reaches the front the outer bulging part here is now called the Kia and that bulge causes refraction of light R so it helps to bend the light rays the aquous humor also helps to bend the light rise and of course our lens will further bend them so they can fall on the retina the image that will fall on the retina it's an inverted image all right in the middle of the eye here's our vitous hum jelly like and it helps to maintain the shape of the eyeball or or teros layer that's the conjunctiva it's a thin transparent layer and it protects the crania sometimes it becomes inflame so that a person suffering from pink eye or conjunctive bitis all right so let's go to the back of the eye know we have the structure called the optic nerve that carries the impulse from the retina to the brain so we said an inverted image falls on the retina but once it goes to the brain the brain will interpret it and we we're able to see things the correct way the spot where the optic nerve leaves the eye that's there are no light sensitive cells there that's called the blind spot right so there are some external structures like your eyelashes your eyelid the eyebrow those also serve a function so you can deduce a function for all three of those I told images form we have an object and the light rays will bounce on the object and bounce off it will then enter the eye where some refraction takes place bending of our light rays so they'll Bend through the pupil they'll fall on our lens and eventually form an inverted image at the back on the retina that information is sent to the brain by the optic nve all right so on the retina also we have these special cells called rods and cones those are our photo receptors the rods allow you to see at low light intensity and you can see in Shades of Black and White while the cones allow you to see at highlight intensity allowing you to see colors now let's look at how the pup is controlled by the iris so the iris muscles they control the the size of the pupil so the pupil is just the opening that allows our light RS to pass pass in in dim light there's our circular muscles they relax and our radial ones contract in bright light we have our circular muscles Contracting and the radial ones relaxing so you should be able to deduce why is it that the pupil is widening in dim light and why is it that it's Contracting in bright light so those are easy deductions the next thing we need to look at is what is called accommodation so we know that there is a b convex lens in the eye here it is it's more of a bulging lens and this lens now will change shape to allow you to see things near and far so that's what accommodation is how the the muscles or hold the lens cheap change your shape to allow you to see distance and near objects in order to see something in the distance we have our CER muscles relaxing the suspensory ligaments will tighten because the the muscles are pulling away from each other they're pulling in the opposite direction so it tightens the ligament and what we find is a flattening of the convex l so it becomes less convex and you're able to see there for near objects now it's the opposite that's happening the muscles they contract they move more inwards towards each other and the this will slatten the ligaments and we have if the ligaments are slack the the lens bulges so that's what we're seeing here the bulging of the lens and it becomes more convex so we're able to see near objects all right so the final thing you need to know about is eye defects and how they're corrected my op here is nearsighted so to see near again we said that we need more of a bulging lens so sometimes the lens in the eye can become too convex so when you're looking at something from a distance it will not fall under retina but it will fall in front of the retina if we're looking at something near it will fall on the retina but we're looking at aant object it converges before the time that's because the lens is too convex so what we need in order to allow the race to diverge is a diverging lens what we call a concave lens so we correct near sightedness by placing a concave lens which will spread out the light rays and allow them to fall under retina let's look at the opposite condition hypermetropia or hyperopia so this is when the lens in the eye it's too flat you're able to see distant objects but near objects will fall behind the retina the image will fall behind the retina appear blurry so because the lens is too flat we correct that with a con conver virgin lens or a convex lens so when we place a con convex lens in in front of the eyes then they'll converge when we looking at a near object it will converge quicker and it falls there again you the reason for this condition could be that the lens is too flat or the eyeball is too short for near sighted the lens is too curved or the eyeball is too long so there are two reasons for each of the condition there are some other conditions for example press B all side this is when the elastic the elasticity of the lens wears out you're unable to see near and far and it's corre corrected with a by focal length it can also be corrected by wearing converging lens a stigmatism on even curve curvature of the lens so the vision appears blurry or dist started and this is corrected using a cylindrical lens there's also glaucoma where there's a pressure build up in front of the eye in the aquous humor this EX exert a pressure on it can exert a pressure on the optic nerve and then it becomes damaged leading to blindness gloma is corrected using ey drop and it can also be corrected using surgery all right so on the screen you're seeing catara so the lens can become opaque or cloudy due to deposits of protein on the lens for this one an artificial lens is given as a replacement