our eyes enable us to see all the beautiful things around us in this video we're going to see the structure of this eye the things that make up our eye when we look at our face it looks somewhat like this is my poor attempt to drawing a face but if you had to concentrate only on the eye and get rid of all the skin then we will be left with a ball and that ball is usually called the eyeball now let's look at this eyeball from the side and let's assume it is transparent so that we can see inside here it is so we'll look at the different major parts of our eyes and we'll also see what each one does so let's start with the one that is most visible to us this one this structure this is called the iris the iris and while people talk about the color of the eye they're actually talking about the color of the iris so when light hits our eyes the light that falls on our iris gets reflected and the color of the light that gets reflected totally depends upon the pigment that makes it up in this case it is green and so we would say that person has green eyes in my case for example it is brown so i would it so my iris reflects brown light and so my eyes are brown in color but notice our iris has a hole in its center and that hole is also given a name it's called the pupil so let's just write that down somewhere over here that hole is called the pupil and as you can see the pupil is through which the light enters into our eyes so through the pupil light will enter into our eyes and this is what enables us to see things now our iris has a very important job its job is to control the size of this pupil the hole and that's because during the daytime or when the ambient lighting conditions are very bright then there are a lot of rays of light that are hitting our eyes so we wouldn't want too many rays of light entering our eyes because in that case that might damage our cells so in such a case what we'll do is our iris will make its hole smaller the pupil becomes constricted so that it only allows the required amount of light to enter our eyes on the other hand if the ambient lighting conditions are very dark so let's say it's evening time or night time or you're inside a dark room now there won't be many rays of light hitting our eyes in the first place now we would want to open up that pupil otherwise you won't be able to see anything and so in such case the pupil opens up the hole opens up allowing the light to enter and you can do this experiment at your home just stand in front of a mirror in in a dark room your pupils will now be dilated and just flash light into your eyes and you will see immediately that people will get constricted become smaller in size all right now let's get rid of the iris so that we can see the other parts of the eye so now we are only seeing a section of the iris it's the same iris with the hole in between all right so let's look at the other parts this burst part of the eye which is in front is called the cornea so this is called the cornea and over here we can see a lens this is called as the lens of the eye so it's just called the lens let's write it down this is called as the lens and the space between the cornea and the lens is filled with a watery kind of a liquid watery kind of liquid and it's called the aqueous humor it's called aqueous because it's watery and if you look at this carefully we can now see that this cornea along with the aqueous humor and the lens they're all convex shaped so the cornea and the lens together form a converging lens system and so whenever you want to concentrate on a specific object their job is to make sure that the light from that object gets focused right at the back part of our eye because it's the back part where we have lots and lots of light sensitive cells so the back part of the eye is completely covered with light sensitive cells which which we are seeing over here in red and so this whole thing is also given a name that's called the retina so let's write that down as well so let's write that down this light sensitive cell covering cell lining is called retina and so in order to see anything clearly the light from that object must get focused exactly on the retina if it doesn't it'll look blurred to us and what do these cells do well these cells once light falls on them they convert light into electricity and finally those electrical signals are carried from the retina all the way to our brain through some nerves so there'll be some nerves that carry all these signals the nerves will connect to all the cells of the retina and all these electrical signals is carried to the brain and this bundle of nerves are called optic nerves optic nerves and then our brain the command center receives these electrical signals does a lot of complex processing and it's eventually able to figure out where those light rays came from and then it constructs the image of the world around us the whole thing is super complicated our brain is super complicated but it's also pretty amazing how it's able to do all of this and by the way the space between the lens and the retina is filled with a jelly kind of transparent substance called the vitreous humor the word vitreous means looks like glass or kind of like glass of course it's not made of glass it's made of organic substance but just like glass it is pretty transparent so it's a jelly-like transparent material and its job is to maintain the shape of our eyes without this humor um our eyes could get easily crushed under the weight of the stuff that is on top of it so the vitreous humor is a transparent jelly-like substance the aqueous humor is also transparent but it's watery kind of substance and the last thing we'll talk about are these fiber kind of things that we see over here which are keeping our lens in place they're called the ciliary ciliary muscles they have a pretty important job too their job is to be able to change the shape of this eye lens well why do we need that well we need that to change the power of our eyes depending upon how far the objects are that we are looking at this will make sense if we draw some rays of light so let's dim all of these things and consider some rays of light alright imagine we are looking at objects which are very far away then the rays of light from that object will be parallel to each other and in order to see it clearly those rays must get focused onto the retina so the ray diagram would look somewhat like this now the important thing is the amount of bending that is required this notice these rays have to be bend by this much amount so as to get focused on the retina and this bending is done by this lens system converging system now imagine that same object were to come closer again to see it clearly the rays of light must get focused onto the retina so these rays will not change but the incoming rays will now be diverging and as a result we will see now the required bending is higher all right so just concentrate on the bending when the object comes closer here it is can you see that the required bending is more more refraction is needed meaning more optical power is needed so when objects are closer we require more optical power more bending and when the objects are farther away we require less optical power less bending so notice our eyes should be able to change its power depending upon how far the objects are and that is accomplished by these ciliary muscles so when the object is far away the required power is less and so the required curvature of our lens is also less in such case the ciliary muscles will be relaxed like like what's shown over here but when the objects come closer since the required power is more the ciliary muscles will start pushing on this lens to increase its curvature as you can see like this i've exaggerated the figure over here it'll push on the lens increase the curvature and as a result it will increase the optical power and that's how depending upon the you know the distance of the object from our eyes the curvature of the lens will keep changing and that is done by these ciliary muscles and this phenomena where ciliary muscles change the power of the eyes by changing the shape of the lens is called accommodation so that's their job their job is to perform accommodation and by the way we're going to look at accommodation in great detail in a future video all right so don't worry too much about this accommodation as of now so that's pretty much it so let's quickly summarize what we learned we saw that the cornea the aqueous humor and the lens together form a converging system whose sole job is to focus rays of light onto the retina the retina contains light sensitive cells whose job is to convert light into electricity these electrical signals are carried out by optic nerves their job is to carry the signal all the way to the brain so that the brain can process the information the jelly-like substance the vitreous humor maintains the shape of our eyeball the iris regulates the size of the pupil which in turn regulates the amount of light that enters our eyes and finally the ciliary muscles regulate the power optical power of our eyes depending upon the waving distance