Opthalmic Artery

We just learned about the Eye Movement.

Another part of the eye is the Opthalmic Artery.

This is what brings the blood up to all of the different parts of the eye.

There are a lot of other arteries that come out of this artery, like the central retinal artery, lacrimal artery, posterior ciliary arteries, muscular branches, supraorbital artery, ethmoidal arteries, medial palpebral arteries and terminal branches.

That's a lot of different arteries for such a small part of the body, but the eye has so many different things going on that there it needs blood in each different place!


(from: wikipedia - opthalmic artery)


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Eye Movement

We just learned about the Fovea in the back of the eye.

Another part of the eye is the group of Eye Movement that move the eye around.

There are six main muscles that move the eye.
Four of them are the "rectus" muscles, and they are attached to the top (superior) bottom (inferior) inside (medial) and outside (lateral) parts of the eye.

Whichever muscle is being used, the eye looks in that direction.
So if the superior muscle is being used, the eye looks up.
If the lateral muscles is being used, the eye looks outward.

The other two muscles are "oblique" muscles, top (superior) and bottom (inferior).
These muscles help control any twisting of the eye, or moving in diagonal directions.


(from: wikipedia - eye movement)


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Fovea

We just learned about the Photoreceptor Cells.

Another part of the eye is the Fovea, sometimes called the fovea centralis, central fovea or fovea of the retina.
The word fovea just means a pit or a depression, and there are other parts of the body that have small pits so sometimes people have to say fovea centralis of the retina to make sure everyone knows which fovea they are talking about.

In the back of the eye by the macula on the retina is a small pit that is full of the cones we talked about.

This part of the eye is where the best sight comes from, when you are focused on looking at something while reading a book or driving a car.


(from: wikipedia - fovea centralis)


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Photoreceptor Cells

We just learned about the Cone Cells.

Another part of the eye is the Photoreceptor Cells.

These are the rods and cones that we already learned about.
The different photoreceptor cells all take light and turn it into chemicals and electrical signals that tell the brain what you are seeing.


(from: wikipedia - photoreceptor cell)


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Cone Cells

We just learned about the Rod Cells.

Another part of the human eye is the Cone Cells.

Cones are different than rods, because they help us see in color.
There are only about 6 million cone cells in the eye, versus about 90 million for rods.
Rods are mostly used just for dark and light, but cones have a different shape so they bring in different types of light.

There are three types of cones in the human eye: S-cones, M-cones and L-cones.
Each type brings in a different type of light.

Remember before we learned about the colors in ROY-G-BIV, Red, Orange, Yellow, Green, Blue, Indigo, Violet.
The colors are put in that order for their "wavelength" which basically just means how the light travels through the air.

The long wavelengths start at the R, G is in the middle, and V is the shortest.
They overlap, and L, M and S cones share some color vision.

L-cones help us see Red, Orange, Yellow and Green.
M-cones help us see Orange, Yellow, Green and Blue.
S-cones help us see Green, Blue and Violet.


(from: wikipedia - cone cell)



(from: wikipedia - color vision)


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Rod Cells

We just learned about the Zonule of Zinn.

Another part of the eye is the Rod Cells.

In the back of the eye at the retina there are things called Rods that help take in light and turn it into a message for your brain to understand what you are seeing.

An adult human has about 92 million rods in one eye!
These rods mostly help see brightness and darkness, and help people see better at night.


(from: wikipedia - rod cell)


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Zonule of Zinn

We just learned about the Uvea.

Another part of the eye is the Zonule of Zinn.

This are the tiny little things like strings that go from the ciliary body to the lens.
Remember the lens is like the magnifying glass that changes shape so you can see far or close,
and the ciliary body is where the muscles are that help push and pull the lens to change it's shape.

It might sound like someone just wanted to come up with a funny name for a part of the body, but the word "zonule" means like tiny zone or tiny area, and the person who discovered this part of the body was named Johann Gottfried Zinn, so he named the area the Zonules of Zinn.

Sometimes it is also called Zinn's membrane, or the ciliary zonule, but Zonule of Zinn sounds the most fun.


(from: wikipedia - zonule of zinn)


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Uvea

We just learned about the Choroid.

Another part of the human eye is the Uvea, also called the vascular tunic.

This is the name for the group of three parts of the eye that we've already learned about: Iris, Ciliary Body, and Choroid.


(from: wikipedia - uvea)


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Choroid

We just learned about the Ciliary Body.

Another part of the human eye is the Choroid.

Remember we learned that the sclera is the white part of the outside of the eye, and the retina is the inside of the eye in the back.

The choroid is a layer in between the sclera and retina.
It helps give blood to the retina, helps hold things together, and also it is dark and helps make sure the retina picks up the light coming in from the pupil.


(from: wikipedia - choroid)


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Ciliary Body

We just learned about the Fibrous Tunic where the Cornea and Sclera are.

Another part of the eyes is the Ciliary Body.

This is made up of two parts: the ciliary muscle, and the ciliary epithelium

The muscle is what squeezes the lens inside the eye to change its shape so you can look at things far away or close up.

The epithelium is what makes the aqueous humour that fills the front of the eye where the pupil is.


(from: wikipedia - ciliary body)


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Fibrous Tunic

We just learned about the Aqueous Humour.

Another part of the eye is the Fibrous Tunic.

We learned before about the clear cornea bubble at the front of the eye, and the white sclera that makes the outside white part of the eye.

These two parts together are called the fibrous tunic.
The word tunic is an old word for clothing that people wore long ago.

Sometimes the words cornea and sclera are smushed together and just called the corneosclera.


(from: wikipedia - fibrous tunic of eyeball)


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Aqueous Humour

We just learned about the Vitreous Body gel inside the eye.

Another part of the eye is the Aqueous Humour.

We know that the eye has different layers.
1 - On the very outside is the cornea, the clear part of the eye that you can touch with your finger.
2 - Then there is the pupil which is the hole letting light in, and the colored iris that helps control the size of the pupil.
3 - Behind those is the lens, which is like a magnifying glass that changes shape to help you focus.

In between those layers is some watery liquid that helps keep everything tightly held in place.
This is the Aqueous Humour, and you can think of it kind of like how a water balloon helps keeps the shape of the balloon.

Aqueous is because it is watery, and Humour means like a liquid.
So the name really means watery liquid.


(from: wikipedia - aqueous humour)


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Vitreous Body

We just learned about the Macula in the back of the eye.

Another part of the human eye is the Vitreous Body.

Inside the eye, most of it is filled up with a kind of clear gooey gel.
It's clear like water, but is thicker almost like jelly.

This is called the vitreous body, or sometimes the vitreous humor.
It helps the eye keep its shape, and it helps keep the vision clear between the lens and the retina.


(from: wikipedia - vitreous body)


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Macula

We just learned about the Sclera whites of the eyes.

Another part of the eye is the Macula.

This is an oval shaped darker spot on the retina in the back of the eye.
The macula helps you see very detailed colors in bright daylight.

If there is a big picture with lots of colors and shapes, your macula helps you see it all clearly.
Sometimes when people get old their macula doesn't work as well anymore, which can cause blurry vision.


(from: wikipedia - macula of retina)


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Sclera

We just learned about the Optic Nerve that brings the eyes signals back to the brain.

Another part of the eye is the Sclera.

This is the name for the white part of the eye.
It is made up mostly of connective tissues called collagen and elastic fiber.


(from: wikipedia - sclera)


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Optic Nerve

We just learned about the Lens in the eye that helps focus light for us to see.

Another part of the eye is the Optic Nerve.

We learned before about the retina in the back of the eye that takes the light from the eye and turns it into signals that the brain can understand.

The retina is connected to a big long nerve called the optic nerve.

This nerve takes the signals from the retina and carries them all the way to the back of the brain, to the part of the brain called the occipital lobe where the signals from the eyes get turned into pictures for the brain to understand.


(from: wikipedia - optic nerve)


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Lens

We just learned about the Retina at the back of the eye.

Another part of the eye is the Lens.

This is a part of the eye right behind iris and pupil.
It is clear and works like a magnifying glass to help the eye focus on things close or far away.

The eye has muscles to push and pull on the lens to change the focus.


(from: wikipedia - lens (anatomy))


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Retina

We just learned about the Cornea.

Another part of the eye is the Retina.

Remember that the black pupil in the eye is really just a hole for the light to come in.
The black color of the pupil comes from the inside of the eye, where the light hits the retina.

The retina is in the back of the eye.
Inside the eye it is shaped like a ball, with the pupil as the hole to let light in, and the retina as inside of the ball at the back.

The retina helps take the light that shines on it, and turn it into signals that are sent to the brain so you can understand what you are seeing.


(from: wikipedia - retina)


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Cornea

We just learned about how we get different Eye Colors.

Another part of the human eye is the Cornea.

This is the clear bubble that is on the front part of your eye.

It works kind of like a magnifying glass, and helps bring light into the eye so you can see.


(from: wikipedia - cornea)


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Eye Color

We just learned about the Iris that opens and closes the pupil.

Another part of the eye is the Eye Color.

The iris we learned about has two parts in it that help make up the eye color.
One is the stroma, and the other is the IPE, which stands for Iris Pigment Epithelium.

That's a lot of big words, but it basically means a bunch of stringy like parts that can have different colors that all blend together to make up your eye color.

The part the really makes a difference is something called melanin.
This is basically like dark paint that your body makes, and the more if it you make the darker your skin, hair and eyes are.

So someone with black hair, dark brown skin and brown eyes has a lot of melanin.
Someone with blond hair, pale skin and blue eyes, has less melanin.


(from: wikipedia - eye color)


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