Main content
Class 10 Physics (India)
Structure of human eye
Let's explore the major parts of our eye, and see what each one does. Created by Mahesh Shenoy.
Want to join the conversation?
- sir can you please make me understand the curvature part of lens?(5 votes)
- If the object is far away, the required curvature of lens is less. The ciliary muscles remain relaxed. During this time, the light rays enter parallelly and are converged on the retina.
But, when the object is near, the required curvature of lens is more. The ciliary muscles has to push the lens to increase its curvature.
During this time, the light rays enter divergently and more focus/bending is needed to form the image on the retina.
Hope it helps:)(6 votes)
- How do the cilliary muscles "push"? I am not trying to be snarky, here. Honest question.(2 votes)
- I'm currently learning about the anatomy and fysiology of the eye. What I've learned is that in order for the lens to become more convex, the muscles of the ciliary body tighten (the musculus ciliaris). As a result the ciliary body is moved towards the lens which results in a decreased amount of tension on the suspensory ligaments (zonula ciliaris). The decreased amount of tension results in the relaxation of the lens, so that it becomes more convex. I really hope this is a helpful and that my explanation is correct. English isn't my native language so if there are any mistakes when it comes down to grammar or something similar, I'm very sorry(4 votes)
- what is the name of the liquid pls?(3 votes)
- There are 2 liquids present in the eye.
Between the cornea and the iris lies the watery aqueous humour.
The other liquid between the lens and retina is vitreous humour which is a transferring kind of substance that looks like glass and is made of organic materials.
Hope it helps:)(2 votes)
- can your cornea like... fall off?(2 votes)
- yes, it can fall off
this is called recurrent corneal erosion in which the outer layer of cornea known as epithelium is loosened or peeled off.
{source help: google}(2 votes)
- What determines the color of the iris? Is it melanin alone?Recently I heard it was due to the presence of some tissues in the eye. Is it true?(2 votes)
- The color of eyes may also generally occur due to the presence of that color in your genes.
The color of iris is usually dependent on hereditary features.(2 votes)
- Hi, Can u please tell the what's the stimulus, the receptor and the effector in blinking?(2 votes)
- Stimulus = harsh, bright light, a dry cornea, dust or any foreign material in your eye, etc
Receptor = photoreceptors inside our eyes
Effector = eye and eyelid muscles closing our eyes(1 vote)
- what is the exact size of the eye?(1 vote)
- Isn't it the cornea's job to do most of the refracting? It does 80% and the lens does 20%.(1 vote)
- The cornea is the clear window through which light can enter. The lens is the main part that focuses the light onto our retina.(1 vote)
- Great Job, thanks(1 vote)
- does the aqueous humor also help in converging the incoming light?(1 vote)
Video transcript
- 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, that's my poor, attempted drawing of face, but if you were to
concentrate only on the eye and get rid of all the skin, then you would 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. Let's start with the one
that Is most visible to us, this one. This structure. This is called the iris. The iris. And though 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 you would say that
person has green eyes. In my case, for example, it is brown, so my iris reflects brown light, and so my eyes are brown in color. But, notice our iris has
a hole in it's center. 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. 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. It's 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. 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 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 your 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 a dark room, your pupils will now be dilated, and just flash light into your eyes, and you will see immediately that pupil will get constricted and
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. This is the same iris with the
hole in between, all right? Let's look at the other parts. This bulge 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 that 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 humour. It's called aqueous because it's watery. And, if you look at this carefully, you can now see that this cornea, along with the aqueous
humour, and the lens, they're all convex shaped. The cornea and the lens together form a converging lens system. 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 we are seeing over here in red. This whole thing is also given a name, that's called the retina. Let's write that down, as well. So, let's write that down. This light sensitive cell
covering, cell lining, is called retina. 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. 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, they'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 transference substance called the vitreous humour. 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. It's a jelly like transferring material and it's job is to maintain
the shape of our eyes. Without this humour, our
eyes could get easily crushed under the weight of the
stuff that is on top of it. So the vitreous humour is a transferring, jelly-like substance. The aqueous humour 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
you draw some rays of light. So, let's dim all of these things, and consider some rays of light. All right, 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. Notice that 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? 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 they require more optical
power, more bending, and when the objects are farther away they require less optical
power, less bending. 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. When the object is far away,
the required power is less, and so the required curvature
of our lenses is also less. In such case, the ciliary
muscles would be relaxed, 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 it's 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 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 phenomenon where ciliary muscles change the power of the eyes by changing the shape of the
lens is called accomodation. 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. That's pretty much it. Let's quickly summarize what we learned. We saw that the cornea, the
aqueous humour, 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. There 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 humour, 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 viewing distance