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Eye Model and Blind Spot Test

Introduction
Public summary: 

Use our amazing model of a human eye to see the intricate structures which allow us to see the world.

Anatomical model of an eye with removable parts to show the structures inside.
Useful information
Kit List: 

Eye Model (of which there are two - use the big new shiny one on its own, the older grubbier one is useful in conjunction with eyeball dissection at CBS!)

Packing Away: 

Lives in small blue medic box along with prism goggles

Frequency of use: 
1
Explanation
Explanation: 


Eye Model

Kids often just enjoy taking the model apart and putting it back together. I often find it engages them more if you make it into a "jigsaw" game - but explain basic bits as they try and put it together.

- Ask them what eyes are for: they will say "seeing", but try and get them to think of it in terms of a light detector. Can use it to see: colour, brightness, outlines and movement. Get them to imagine how life would be without eyes. A way of getting info from outside into our brain.

- Ask if they recognise and can name any bits of the eye. Most of the time incorrectly say the clear plastic bit on the outside of the eye is the lens. It's the cornea, mention protection and also cataracts - they won't know the name but they will have seen old cats and dogs with cloudy eyes, or they may have grandparents with the condition.

- Pupil is actually hole (wow!) in middle of eye - lets in light. What happens to your pupil when you go into a dark room....some will answer correctly. Ask them why - because you want more light to reach retina. Can also relate this to doctor's shining lights in people's eyes to check pupil reflexes. Why get smaller in bright light? - to protect eye from damage.

- Iris, they don't normally know the name, but ask what its for and why it can be different colours.

- Lens - ask them what it looks like, some say glasses/contact lenses so this is a good start (although I've had sherbet flying saucers as one answer). Explain that lens bends picture so that it lands on back of eye. With long/short sighted people, the lens is too fat or thin so that picture lands infront or behind retina - that's why it's all blurry. When people get older, the lens gets less stretchy, and therefore they might need glasses when they maybe didn't before. Ask them how that is fixed and talk about needing another lens to correct it i.e. glasses.

- The light has to go through see-through stuff in the middle of your eyes (a bit like jelly). It see through because the light has to get to the back of our eye for us to see.

- Retina - could side track slightly into 'what are cells?' etc. Do all cells do the same thing? No - skin, heart etc do different things, and these cells are very special because they can tell us about the light in the world around us. If you fancy talk a bit about colour/ colour blindness. Get across the idea that in the most common sort of colour blind people its not that they can't see colour, just that they find it difficult to distinguish between colours (then could compare this to rarer sorts/cortical colourblindness).

-Compare the eye to a camera: "takes pictures of the surroundings" which are then sent to the brain by the optic nerve. Explain how it is your brain that works out exactly what you are seeing "e.g. duck or rabbit". Can get confused sometimes - optical illusion (there should be some sheets with optical illusions around which you can use to elaborate if you wish). Also that different parts do different things (like motion, colour, faces) - what would happen if these bits got damaged?
- Explain the brain also corrects for other problems - talk about and find blind-spot (there should be a test sheet). Sometimes hard to explain to younger kids.
- Most kids will talk about how the image is inverted and the brain flips it up the right way. But if they don't could put it in.

- Eye muscles and eye movements - get them to watch you keeping your head still but moving your eyes if theyre not convinced. Could talk about why you have two eyes e.g. to tell how far away things are. And differences between how a horse sees and how you see. You can also use this as an opportunity to talk about how nerves are 2 way - so theres the big one telling your brain about what your seeing, but your brain also needs to control how your eyes move with nerves too.

- Often they ask why we blink - so talk about tears and cleaning/protecting your eyes. Also can ask if theyve noticed getting a runny nose when they cry, thats because iof lots of extra tears going down your tear ducts into your nose.

- Mention blood vessels on surface of model, artery, vein and nerves.
- What is eye cavity made of..... surprising number of kids won't get this. And ask what the holes in the bone are for.....blood
- Ask them what the space behind the eyeball would normally be filled with in us. Say it's for protection and lead them on with hints to say fat. I normally do this by saying how some people have a lot of it around their tummies.


Blind Spot Test

TO DO:

•Let the kids find their blind spots using the first diagram
•Close/cover the left eye – get child to stare at cross mark in diagram with right eye
•Off to the right they should be able to see the spot – check they can (but they shouldn’t look at it directly!)
•Get the child to move slowly towards the diagram/bring the diagram closer towards their eye while still looking at the cross mark
•At a particular distance the spot will disappear (it will reappear again if you move closer)
•Kids often get quite excited and move the paper quite fast which means they miss the point when they can see their blind spots – important to make them slow down!
•Second and third diagrams are to reinforce the principle that the brain “fills in” what it can’t see – should see a yellow background in the second picture, and in the third picture, the line should complete

EXPLANATION:

•Start by talking about the basic structure of the eye (using an eye model – kids will often already know quite a bit)
•Inside our eye there is a “black screen” called the retina (you can see this when you look through your pupil – that’s why the pupil is black)
•Retina is a bit like a TV screen/camera – there are lots of detectors that “see” light
•Brain changes this light into a picture
•How does the light get from the screen in the eye to the brain? Travels down a “path” called the optic nerve
•At the point where the optic nerve leaves the eye – no light can be detected on the retina (no photoreceptors to respond to light) – brain gets no information from the eye about this particular part of the picture of the world
•Because of this – have a blind spot! But why do we not notice them normally?
•Most people assume that what you see is pretty much what your eye sees and reports to your brain – brain actually adds very substantially to the report it gets from your eye, so a lot of what you see is actually “made up” by the brain – brain fills in the picture according to what it “thinks” it should look like

OTHER THINGS TO TALK ABOUT:

Do all species have a blind spot?:
No. Interestingly an octopus does not have a blind spot! The retina of the octopus is constructed more logically than the mammalian retina. The photoreceptors in the octopus retina are located in the inner portion of the eye and the cells that carry information to the brain are located in the outer portion of the retina. Therefore, the octopus optic nerve does not interrupt any space of retina.

Risk Assessment
Date risk assesment last checked: 
Fri, 25/01/2019
Risk assesment checked by: 
Matt Worssam
Date risk assesment double checked: 
Sat, 02/02/2019
Risk assesment double-checked by: 
Esmae
Risk Assessment: 

Various medical models.

Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Small parts Small parts could be swallowed. 2 4 8 Do not let children play with experiments unattended. Call first aider in case of ingestion and encourage the child to cough. 1 4 4
Broken parts If broken parts could be sharp. 2 2 4 Remove broken models. Call first aider in case of injury. 1 2 2
Pointed parts Some parts have fairly sharp points - risk to eyes/skin. 3 2 6 Sharp points filed down to be as safe as reasonably possible. Call a first aider in case of injury. 3 1 3
Reduced Vision when Using Blind Spot Test Reduced vision may increase risk of tripping. 2 2 4 Mark boards with highly visible stuff (e.g. hazard tape, white paper) if they are being used in the dark room.
Get people to remain still.
Call a first aider in the event of injury.
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