Our senses: How does vision work?

Do it yourself

Did you know that there are some animals that do not have eyes? These animals include jellyfish, starfish and especially animals in the deep sea. Since there is no light there, deep-sea animals have regressed their vision and specialised in other senses. For humans this is unthinkable, as for us the eyes are the most important sensory organ. We perceive the majority of all impressions of our environment through our eyes and rely heavily on them. 


We'll show you some exciting experiments that will make you discover more about your eyes. With our instructions, you can even make your own artificial eye and challenge your friends.

Let's go - have fun!

You want to know more about the eye?

How exactly does the eye work? How do we see? Why do some people need glasses or contact lenses?
Below you will find additional information about the sense of sight and links to information material that we have found online on the topic! Also check out Part 2 of our series: Of all the Senses: Optical Illusions.


  • Suitable for age group: 9 years and older

  • Especially interesting for: Children and teenagers, people who like to experiment, future scientists and doctors

  • Preparation time: about 10-30 mins per experiment

Experiment 1: How seeing works

With this experiment you can illustrate the processes in the eye and thus better understand its structure.


  • You need:

  • Globe-shaped glass (goldfish bowl, globe vase, bowl dish... approx. 20cm in diameter)

  • Tissue

  • Adhesive tape

  • Magnifying glas

  • Scissors

  • Modelling clay

  • Cardboard

  • Flash lamp


Step 1: Attach tissue to the bowl

Stick the tissue to the outside of the glass with adhesive tape. In this experiment, the tissue is the retina of the eye, i.e. the projection surface. The globe vase represents the human eyeball.

Step 2: Cut out figure

Draw a figure (approx. 4cm) on the cardboard paper, where the top is clearly different from the bottom, and cut it out. This figure is the image we see as soon as we look at something.
Remember: the bigger your figure is, the more space you will need at the end.


You are completely free to decide what kind of figure you want to cut out. There are almost no limits to your imagination, just remember that it should not be a circle or something similar.

Step 3: Set up magnifying glas and figure

First place the magnifying glass, then the figure in front of the glass with the help of the modelling clay. In this case, the magnifying glass is the lens of the eye. You will have to adjust the distance between the glass, the magnifying glass and the figure later so that you get a sharp picture.


The more powerful your magnifying glass, the less space you will need in the end. Of course, the experiment also works with a cheaper or simpler magnifying glass, you just need a little longer and more space (calculate with metres, not centimetres) to focus.

Step 4: Light up

Shine the flash lamp on the figure so that the light falls through the magnifying glass and the globe onto the paper towel. The light falls through the figure onto the magnifying glass. The lens then refracts the light rays and an image is created. This refraction causes the image to be upside down/reversed and reduced in size on the "retina".

Explanation and additional information

But why is the picture upside down and why is it smaller than before? Normally, a magnifying glass is used to enlarge images or text. The answer can be found in the rules of physics. The glass of the magnifying glass has a certain shape, namely a convex converging lens. This means nothing other than that the lens is bent outwards in a C-shape and the light that falls in is bundled and not scattered (mnemonic: concave has the word cave in it and means “hollowed or rounded inward like the inside of a bowl”.). It looks approximately like in the drawing. On the left side is the original (the image), in the middle you see the lens, while on the right side is the portrayal, i.e. what arrives on the retina in our experiment.

After this experiment, you might ask yourself why the whole world doesn't turn upside down for us then. This is because the human brain is extremely powerful. After the mirror-inverted, reduced image hits the retina (tissue), it sends the corresponding signals to the brain (primary visual cortex) with the help of the optic nerve. There, the image is then turned around so that it is "upright". But how does our brain know what is "right"? This is a difficult question that is still much debated. What is known, however, is that our sense of touch and interaction with the environment helps us to do this. You can easily test this yourself with a pair of so-called inversion glasses. These glasses turn everything you see upside down. If you wear them for a few days, your brain gets used to them and makes sure that everything is the " correct " way up again.

But our visual system can do much more. Since our brain is largely concerned with seeing, "shortcuts" (i.e. simplifications) have been developed for evolutionary reasons. This is why the human brain prefers patterns and can fall for optical tricks. So optical illusions are strongly related to our expectations, experiences and focus. Why not try it out for yourself in the second part of our seeing series?

Experiment 2: Detection of the blind spot

Our eyes reliably perceive what is happening around us. Therefore, it is hard to believe that there is nevertheless a spot in the eye that has no vision. With the following experiment, the blind spot can be unmasked!


  • You need:

  • A willing subject (test person)

  • Our print template or a screen (larger than a mobile phone display)


Below this text you can see a squirrel and a hazelnut. Get your face close to the screen or print out the template and hold it close to your face. Cover your left eye and look very closely at the squirrel with your right eye. The squirrel should be right in front of your right eye. Now you can slowly move away from the drawing, but without changing your line of sight! At a certain distance, the hazelnut seems to disappear as the image hits the blind spot.





The retina is located in the back of our eye. It contains a large number of sensory cells that receive information about the incoming light and pass it on to the brain via the large optic nerve. The area where the optic nerve exits the eye is called the blind spot because there are no sensory cells here. This is the only area without nerve cells; there are many sensory cells in all other parts of the retina. You can also see the blind spot in the photo of the retina. In everyday life, you normally don't notice it because your brain fills this spot with other image information. In this experiment, instead of the drawing, you see at least the white of the paper or screen. You just do not see the hazelnut because your brain does not receive any information about it as long as the image is located in the blind spot.

Have fun
trying it out!

Learn more!

Structure of the eye



You probably already know that the human eye is a somewhat asymmetrical sphere and is made up of many parts. If you pull your eyelid up a little, you can see the spherical shape. The eyeball is embedded in the eye socket and almost completely covered by a protective sclera. The sclera is the white part of your eye. It is covered in the front, visible area by a thin, moist conjunctiva. At the front of the eye is the iris, which acts as a shutter. It determines how much light

enters the black opening in the centre of the iris. So when you ask someone about their eye colour, you are asking about the colour of the iris. The black circle inside the iris is the pupil. The pupil is also called the eye hole and is a small opening through which light can enter the eye.

In front of the iris and the pupil is not the sclera, but the so-called cornea. The cornea is curved and thus forms a small chamber that is filled with fluid. The task of the cornea is to refract incident light. In order for the light to enter the eye at all, the cornea is completely clear and transparent and not white, like the sclera. Inside the eye, directly behind the pupil, there is a lens which has the same function as the cornea. However, the refraction of the cornea and the anterior chamber is greater because liquids have a stronger refractive power than air.






The inside of the eye is completely filled by the so-called vitreous humour. It consists almost entirely of water and provides stability. The rear part of the eye is covered by another skin, the retina. This is covered by a large number of nerve cells that convert light into an electrical signal and transmit it to the brain via the optic nerve.

Visual impairments and visual aids

Some people have slight changes in the structure of the eye and can therefore see more poorly or blurred. Such visual impairments may already be congenital or may only occur during the course of life and have very different causes.

Short-sightedness and long-sightedness

You are probably familiar with these two visual defects. The problem here is that the image does not fall directly on the retina, but is focused in front of or behind it, and the affected person thus sees out of focus at certain distances.

In shortsightedness (myopia), this may be because the eyeball is too long or the refractive power of the lens and cornea is too strong. As a result, the image is already displayed in front of the retina.                      

With farsightedness (hyperopia), it is exactly the opposite. The causes are therefore a too short eyeball or a too weak refractive power of the lens and cornea, so that the image is shown behind the retina.


However, short-sightedness and long-sightedness can be compensated well by an artificial lens, i.e. glasses or contact lenses. These lenses are divided into diverging and converging lenses. Diverging lenses help short-sighted people to compensate for excessive refractive power and converging lenses provide additional light refraction for long-sighted people.

Myopia with diverging lens:

Hyperopia with converging lens:

Colour vision deficiencies: Example of red-green deficiency

Colour vision deficiencies are colour sense disorders and are genetically determined.
They are therefore already congenital, but fortunately do not get worse in most cases.
The best-known form is red-green deficiency, in which those affected can hardly distinguish between these two colours.

The reason for this colour vision deficiency is a disorder of the sensory cells on the retina.
There are three different types of cones, which have receptors for red, green and blue light. People with this visual impairment have a disorder in the receptors for red or green light.
The receptors hardly react or do not react at all to light with the corresponding wavelength, so the brain does not receive the correct information to determine the actual colour.

This is how people with red-green deficiency see a traffic light.


Although blind people cannot see, their other senses are often particularly sharpened. For example, blind people can read with their fingertips instead of their eyes. The writing is called Braille and uses different patterns with up to six raised dots instead of letters. The sense of touch of blind people is particularly sensitive, so they can recognise the tiny dots and put them into context.


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