Parts of the eye | Human eye & the colourful world | Khan Academy

Summary

This educational video script explores the intricate structure of the human eye, detailing its major components like the iris, pupil, cornea, lens, aqueous humour, retina, and vitreous humour. It explains how the iris controls the amount of light entering through the pupil and how the cornea and lens work together to focus light onto the retina. The script also delves into the role of the ciliary muscles in adjusting the lens's curvature for different viewing distances, a process known as accommodation. The retina's light-sensitive cells convert light into electrical signals sent to the brain via the optic nerves, painting a picture of the world we see.

Takeaways

• 👁 The eye is a complex organ that allows us to see by capturing and processing light.
• 🌈 The iris is the colored part of the eye that controls the size of the pupil, regulating the amount of light entering the eye.
• 🕳️ The pupil is the black hole in the center of the iris that allows light to enter the eye.
• 🔭 The cornea, along with the aqueous humor and lens, forms a converging lens system that focuses light onto the retina.
• 👁️👁️ The retina is a light-sensitive layer at the back of the eye that converts light into electrical signals.
• 🧠 The optic nerves carry these electrical signals from the retina to the brain for processing.
• 🔵 The iris adjusts the size of the pupil in response to light conditions to protect the eye and enhance vision.
• 🔴 The color of the iris determines the color of the eye, which is determined by the pigment reflecting light.
• 🔎 The ciliary muscles control the shape of the lens, allowing the eye to focus on objects at different distances.
• 🌌 The vitreous humor is a jelly-like substance that maintains the shape of the eye and keeps it from collapsing.
• 🔄 Accommodation is the process by which the ciliary muscles adjust the lens's curvature to focus on objects at varying distances.

Q & A

What is the primary function of the iris?

The iris controls the size of the pupil, regulating the amount of light that enters the eye.

How does the pupil react to different lighting conditions?

In bright light, the pupil constricts to reduce the amount of light entering the eye, while in dim light, it dilates to allow more light in.

What is the role of the cornea in the eye?

The cornea is the bulge part of the eye that works with the aqueous humor and the lens to form a converging lens system, helping to focus light onto the retina.

What is the aqueous humor and where is it located?

The aqueous humor is a watery liquid that fills the space between the cornea and the lens, aiding in the refraction of light.

What is the lens of the eye and what does it do?

The lens is a transparent structure that works with the cornea and aqueous humor to focus light onto the retina.

What is the retina and where is it located in the eye?

The retina is a light-sensitive layer of tissue located at the back of the eye, responsible for converting light into electrical signals that are sent to the brain.

How does the brain interpret the electrical signals from the retina?

The brain processes the electrical signals from the retina to construct the image of the world around us.

What is the vitreous humor and what is its function?

The vitreous humor is a jelly-like substance that fills the space between the lens and the retina, maintaining the shape of the eyeball.

What are the ciliary muscles and what is their role in vision?

The ciliary muscles are responsible for changing the shape of the lens to adjust the eye's optical power, allowing us to focus on objects at different distances.

What is the process called when the ciliary muscles adjust the lens shape?

The process is called accommodation, which allows the eye to focus on objects at varying distances.

How do the ciliary muscles change the curvature of the lens?

When objects are close, the ciliary muscles contract to increase the lens curvature and optical power. When objects are far away, they relax, reducing the curvature and optical power.

Outlines

00:00

👁️ Anatomy of the Eye

This paragraph discusses the structure of the human eye, starting with the iris and its color, which is determined by the pigmentation reflected by light. The iris has a central hole called the pupil, which the iris controls to regulate the amount of light entering the eye. The pupil constricts in bright light to protect the eye and dilates in low light to allow more light in. The cornea, lens, and aqueous humor are also introduced as part of the eye's converging lens system, which focuses light onto the retina, a light-sensitive layer at the back of the eye.

05:03

🧠 Visual Processing and the Brain

The second paragraph delves into how light-sensitive cells in the retina convert light into electrical signals that are transmitted to the brain via the optic nerves. The brain processes these signals to construct our visual perception of the world. The vitreous humor, a jelly-like substance, is highlighted for its role in maintaining the shape of the eye. Additionally, the paragraph explains the function of the ciliary muscles in adjusting the eye's optical power, or focus, for objects at varying distances, a process known as accommodation.

10:03

🔍 Summary of the Eye's Functions

The final paragraph summarizes the functions of the eye's major components: the cornea, aqueous humor, and lens work together to focus light; the retina contains light-sensitive cells that convert light into electrical signals; the optic nerves carry these signals to the brain for processing; the vitreous humor maintains the eye's shape; the iris regulates the size of the pupil to control light intake; and the ciliary muscles adjust the eye's optical power for viewing objects at different distances.

Keywords

💡Eyeball

The eyeball is the spherical organ of sight in humans and many animals, filled with a jelly-like substance. In the video, it is described as a 'ball' that is usually transparent to allow the viewer to see inside its structure. The eyeball is the primary focus of the video, as it houses all the components necessary for vision.

💡Iris

The iris is the colored, ring-shaped membrane determining eye color and controlling the size of the pupil. It is central to the video's discussion on how the eye functions, as it regulates the amount of light entering the eye by adjusting the size of the pupil. The script explains that the color of the iris, which can be green or brown as examples, is what people refer to when they talk about 'eye color'.

💡Pupil

The pupil is the black circular opening at the center of the iris that allows light to enter the eye. The video emphasizes its importance as the gateway for light, which is essential for vision. The size of the pupil changes (dilates or constricts) to control the amount of light entering the eye, adapting to different lighting conditions.

💡Cornea

The cornea is the transparent front part of the eyeball that covers the iris, pupil, and anterior chamber. In the video, it is part of the converging lens system along with the aqueous humor and the lens, playing a critical role in bending light rays to focus them on the retina.

💡Lens

The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to focus light onto the retina. The video explains that the lens works in conjunction with the cornea to form a converging lens system, which is vital for focusing light on the retina to create a clear image.

💡Aqueous Humour

The aqueous humor is the clear fluid that fills the space between the cornea and the lens. As mentioned in the video, it is watery in consistency and, along with the cornea and lens, forms part of the eye's converging lens system, aiding in the focusing of light.

💡Retina

The retina is the light-sensitive layer of tissue at the back of the eye, containing cells sensitive to light. The video describes the retina as being covered with light-sensitive cells that convert light into electrical signals, which are then sent to the brain via the optic nerve, allowing us to see.

💡Optic Nerve

The optic nerve is the bundle of nerve fibers that transmit visual signals from the retina to the brain. The video highlights that these nerves carry the electrical signals generated by the retina's light-sensitive cells to the brain, where the information is processed to create the images we perceive.

💡Vitreous Humour

The vitreous humor is the clear, jelly-like substance that fills the large space in the center of the eyeball between the lens and the retina. The video explains that it maintains the shape of the eyeball and prevents it from being crushed under the weight of the tissues above it.

💡Ciliary Muscles

The ciliary muscles are the muscles surrounding the lens and are responsible for changing the shape of the lens, which adjusts the eye's focus. The video describes how these muscles contract or relax to alter the lens's curvature, allowing the eye to focus on objects at varying distances, a process known as accommodation.

💡Accommodation

Accommodation is the process by which the eye adjusts its focus to see objects at different distances clearly. The video explains that the ciliary muscles change the shape of the lens to increase or decrease its optical power, allowing the eye to focus on objects whether they are near or far.

Highlights

The eye's structure is essential for seeing the beauty around us.

The eyeball is a ball-like structure at the center of the face.

The iris is the visible structure that determines eye color.

The iris color reflects the pigmentation, such as green or brown.

The pupil is the central hole in the iris that allows light to enter the eye.

The iris controls the size of the pupil to regulate the amount of light entering the eye.

In bright light, the iris constricts the pupil to protect the eye from damage.

In dim light, the iris dilates the pupil to allow more light for better visibility.

The cornea is the bulge part of the eye that helps focus light.

The lens is a part of the eye that works with the cornea to focus light.

Aqueous humour is the watery liquid between the cornea and the lens.

The cornea, aqueous humour, and lens form a converging lens system.

The retina is the light-sensitive cell lining at the back of the eye.

Light-sensitive cells in the retina convert light into electrical signals.

Optic nerves carry electrical signals from the retina to the brain.

The vitreous humour is a jelly-like substance that maintains the eye's shape.

Ciliary muscles adjust the shape of the lens to focus on objects at different distances.

Accommodation is the process by which ciliary muscles change the lens' power for focusing.

The eye's structure and functions are intricately connected for optimal vision.

Transcripts

- 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