Professor Hallux Builds a Body

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Episode 4 – Ingenious Eyes

How do eyes work?

hallux-leaningHello medical magpies and welcome to my blog post about building my very own human body.

Today Nurse Nanobot and I added some lovely wobbly bobbly eyeballs.

Of all the body parts, eyes are quite the most clever.  And did you know that your eyes are the same size in your sockets as they were on the day you were born? That’s why babies’ eyes look so big!

Press the play button above to listen to us explore the world of eyes and also read loads of interesting facts below!

All the Different Parts

The white part of your eye is called the sclera.  It contains the blood vessels that bring nutrients to your eyes.  The transparent part at the front of the eye is called the cornea.  Behind this is the iris, the coloured part of your eye, and behind this is a lens made of a firm jelly. Together the lens and iris help the eye to focus.

What Eyes and Bottoms Have in Common!

Did you know that the iris is far more than just the coloured part?  Its actually a sphincter muscle – that’s a muscle that tightens like a drawstring bag.

The most well known sphincter muscle is in your bottom – it’s the one that keeps the poo in!  But in your eye it keeps light out by tightening up when it’s too bright – that’s why your pupil looks like it is getting smaller in bright light – try looking in a mirror and changing the light near your eye with a torch.


Our eyelids help to keep eyes clean and moist through a very complicated process called….. blinking!  Blinking is both a voluntary and involuntary action, meaning you can blink whenever you want to, but you also blink without even thinking about it.  Eyelashes also help to protect the eyes, just like umbrellas.

Another way your eyes keep themselves clean is by watering when there’s something getting in the way like dust or an eyelash.

In Your Eye

nanobot-skeletonThe insides of the eyeball are really cool, but you can’t see them with just your own eyes! Opticians and doctors use special a microscope called an opthalmoscope to look at these inner parts of the eye.

The biggest part of the eye sits behind the lens and is called the vitreous body.  It accounts for two thirds of the eye’s volume and gives the eye its shape. It’s filled with a clear, jelly-like material called the vitreous humor.

After light passes through the lens, it shines straight through the vitreous humor to the back of the eye which is where the retina is.


The retina is like a movie screen onto which the light from outside is projected.  Special cells called rods and cones process light.  There are around 120 million rods and 6 million cones in each eye! So what do they all do?

Rods see in black and white, and in shades of grey and tell the form or shape that something has.  Although rods can’t tell the difference between colours, they are super-sensitive, and allow us to see even when it’s dark.

Cones sense colour.  They need more light than rods to work well.  There are three types of cones – each type being sensitive to one of three different colours – red, green or blue.

Together, these cones can sense combinations of light waves that enable our eyes to see millions of colours.

halluxTogether, rods and cones process the light to give you the total picture.  The information from the rods and cones is whizzed up the optic nerve to your brain where the images are processed!

The image from the lens actually shines onto the retina upside down, but your brain flips the picture without you even knowing!

Did you know that if you look at a colourful jumper in a very dark room you’ll have trouble to see which bits are red and which are green – but you’ll probably be able to see the pattern, that’s the rods and cones in action!

Nurse Nanobot’s Orrible Old Anatomy Fact

nanobotDo you wear glasses or know someone who does, or even why they do?  The eye’s squishy, stretchy lens is surrounded by muscles called ciliary muscles which contract to change the lens between fat and thin.

The lens’ thickness changes when you look at things that are close or far away so that the image is projected perfectly onto the retina. If these muscles can’t change the shape of the lens quite enough, things might look blurry, and that’s why people wear glasses or contact lenses – to give the eye’s own lens a bit of help!

Cataracts are an eye condition where the lens goes cloudy and mainly happens when you get old.

Surgeons today can replace them with a plastic lens, but did you know that surgeons have been trying to remove cataracts for over 2000 years?

Bronze age instruments have been found that pushed the lens into the back of the eye and another gruesome way was for getting them out was to suck them out with a straw!hallux-bodyparts

Disgusting Details

Did you know that in many parts of the world, eating animal’s eyeballs, often sheep or goat’s eyeballs, is considered perfectly normal – even said to be a delicacy!

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Professor Hallux Builds a Body

Find out out how to build a human body with Professor Hallux and Fun Kids

More From Professor Hallux Builds a Body