Fun & Games

This is the fun part. Find out how far an eagle can see and how many eyes a scorpion has in our amazing facts. Take a tour around an eye with our special video. Then, when you're all clued up, be astonished by our colourful optical illusions. Learning has never been more fun.

Amazing Eye Facts

Eagle

How far can an eagle see?

A lot further than the human eye can see. An eagle can see a rabbit about 1 mile away.

Rabbit
Scorpion

How many eyes?

A scorpion may have as many as 12 eyes. Some marine flatworms have more than 100 eyes scattered all over their bodies!

Flatworm

The Human Eye

Your eyes are amazing. Take a look at the picture below and you'll see a detailed cross- section of an eye. It looks rather strange when you see it like this, but each part of your eye has an important role to play in helping you see the world around you.

You can see your eyelids, lashes and iris every day, but what happens behind the eye? This is your chance to find out. To read more about each part, just click on the yellow letter.

The Human Eye

A: Cornea

Completely clear, steeply curved 'window covering' at the very front of the eye. Provides the main refracting (light bending) surface of the eye.

B: Anterior Chamber

The space between the back of the cornea(A) and the Iris(E). Filled with clear substance called aqueous humour which helps provide nutrition to the cornea and lens. Aqueous humour is created in the ciliary body(N).

C: Pupil

The opening or 'hole' in the centre of the Iris through which light entering the eye passes. The hole varies in size dependent upon the amount of light present. The darker the light conditions the larger the pupil 'hole' becomes. This process is known as 'dilating'.

D: Crystalline Lens

Lies immediately behind the pupil. The crystalline lens is one of the other refracting elements of the eye and is often simply referred to as the lens. Its purpose is to focus light onto the retina. The lens is transparent and made up of several layers, rather like an onion. The lens is very flexible and muscles situated in the ciliary body (N) are able to change its shape. This enables light entering the eye to be accurately focused on to the retina (J) at the back of the eye.

E: Iris

This is the 'coloured' part of the eye and is located immediately in front of the lens(D). It is the Iris that contracts and expands causing the pupil(C) to vary in size. Everyone's iris contains varying amounts of 'pigment'. The more pigment present, the darker the eyes will appear. A lot of pigment will cause the eye to appear to be brown, less will cause them to look green or grey and a lack of pigment will cause them to be red.

F: Vitreous Body

This is the main chamber of the eye. Its function is to allow light to travel to the retina, and contain the correct internal pressure of its vitreous fluid to maintain the shape of the eye and allow the very sensitive parts of the eye to function correctly

G: Optic Disc

This is the front surface of the optic nerve(H), which is visable on the retina(J). It is where the nerve fibres meet the retina. The area around the the optic disk has no visual receptors and is often reffered to as the blind spot

H: The Optic Nerve

This acts like a cable connecting the eye with the brain.

I: The Retina

This is the lining that covers a very large area of the inside surface of the back of the eye. It is a multi-layered, sensory tissue, the purpose of which is to convert light energy into electrical nerve impulses, which are taken to the brain via the optic nerve.

There are two types of receptors within the retina - these capture light rays and are known as rods and cones. The central part of the retina (fovea(J)) contains a very high density of cones and no rods. Cones are used to identify detail but require good lighting to work correctly. The concentration of rods increases away from the central region. Rods are much less light sensitive and as such work well in low light conditions but are poor at resolving detail.

J: Fovea

This is the area of the retina (J) where the greatest concentration of 'cone' light sensors exist. Around the fovea is the 'macular region'. It is also the part of the retina that light forms upon when we look directly at something. As such it forms our 'central' vision. The central part of our vision is much more sensitive and is what we use to study an image.

Our outer vision is known as peripheral vision. There are fewer cone sensors in the outer sections of the retina where images form in our peripheral vision. As such, the periphery of our vision is used to detect such thing as light or movement rather than detail.

Our natural reaction is to then focus directly upon any such light or movement, bringing the image into our much more sensitive central vision.

When we test someone's eyes, the main vision test occurs when the letter images are forming on the highly sensitive fovea. We can also, if required, carry out some additional peripheral vision tests. This usually requires the patient to look straight ahead and detect a series of marks or lights plotted around their peripheral vision.

K: The Choroid

The inner layer between the retina(I) and sclera(L) and is made up from blood vessels. Main function is to provide outer layer of retina with nourishment and remove their waste products.

L: The Sclera

The extremely tough, collagen, protective outer layer of the eye. It protects the delicate inners of the eye and holds them in place to allow for consistent 'refraction' to take place. In a normal healthy eye, the sclera will appear to be white (hence the white of the eye).

In a young child the sclera may be thinner and appear slightly blue. Deposits of fat or jaundice can give it a yellow appearance and many conditions can cause it to become red.

M: Conjunctiva

The thin transparant tissue that covers the outer surface of the eye. Allows the eye to move freely and produces response to any foreign body entering the front of the eye. The sac will stop anything going into the 'back of the eye' a worry for some contact lens wearers. The conjunctiva also secretes oils and mucous that moisten and lubricate the eye.

N: Ciliary Body

Similar in structure to Iris(E). Area that creates the aqueous humour. It also contains the ciliary muscle - a structure vital to enable the eye to focus on near and far objects, by changing the shape of the lens(D) - this process is known as accomodation.

O: Posterior Chamber

Fluid filled space immediately behind the iris but in front of the lens.

P: Zonule

The suspensory ligament of the crystalline lens of the eye. Can be likened to 'guy lines'. These attach to the ciliary body(N) and the lens(D) capsule.

Q & R: The Eyelids and Eyelashes

The principal function of eyelids and eyelashes is to protect the exposed front of the eye. The lids also assist in moving tears over the eyes, and of course stop light entering the eye when we close them.

Q & R: The Eyelids and Eyelashes

The principal function of eyelids and eyelashes is to protect the exposed front of the eye. The lids also assist in moving tears over the eyes, and of course stop light entering the eye when we close them.

S: Extrinsic Muscles

There are 6 muscles attached to the outside of the eye which join it to the eye socket. These work together, or in opposition, to enable the eye to rotate freely and accurately. The eyes should be able to rotate individually, but in a controlled manner, to ensure that the image falls on the desired position on the retina of each eye. The brain can merge these images together and form a single image. Failure to achieve this can result in potential 'double' vision which may have to be corrected by 'prism' being prescribed.

Have you ever wondered what your eye really looks like? Take a 3D tour here. There'll be lots of parts you recognise, but there's also a chance to go behind your eyes and look at the parts you'll never get to see.

Watch the Eye Video

Optician Illusion

Play fun tricks on your eyes with our amazing optical illusions. Can you answer the questions correctly?

Neon Colour Spreading

Watch as the blue lines create a blue square right before your eyes.

View this illusion

The Ebbinghaus Illusion

Look closely and guess which grey circle is bigger.

View this illusion

Top Hat Illusion

Take a close look at the hat and answer the question about its size.

View this illusion

The Height of Estimation Illusion

Can you work out how high the red dot is on the triangle?

View this illusion

The Müller-Lyer Illusion

How good are your measuring skills? Try them out here.

View this illusion

Chromatic Colour Assimilation

See if you notice anything special about these red squares.

View this illusion

Shepard's Tabletop Illusion

How much do these tables have in common? Take a look.

View this illusion

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