What it shows
Where the optic nerve leaves the retina there are no light-sensing cells, so a small spot in each eye cannot see. A cross and a dot on a card show the dot vanishing when its image falls on this blind spot.
The science
Light falling on the retina is turned into signals by rod and cone cells. At the point where the optic nerve fibres gather and leave the eye there are no such cells, so any image falling there is not seen. We do not notice this in daily life because the other eye covers the gap and the brain fills it from the surroundings. The blind spot lies about 15 degrees to the outer side of the centre of vision.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A white card about 15 cm by 10 cm
- A black marker
- A ruler
- A friend or a mirror
- A notebook
Safety
For this project: No special hazard. Do not stare for long and take a short rest if your eyes feel tired.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Draw a black plus sign on the left side of the card and a black round dot about 1 cm wide on the right side, about 8 cm apart.
Hold the card at arm’s length with the plus on the left side. Close your left eye.
Look at the plus with the right eye only and keep looking at it without moving the eye.
Slowly bring the card towards your face and note the distance when the dot suddenly disappears.
Measure the distance from the eye to the card with a ruler and note the distance between the cross and dot.
Move the card further and the dot comes back. Repeat three times and write the average distance.
Reverse the card to test the left eye by looking at the dot with the left eye and closing the right.
Draw the eye with the optic nerve and the blind spot, and label rods, cones and retina next to your card.
What you should see
At about 25 to 30 cm for a distance of 8 cm between plus and dot, the dot disappears completely and returns when the card moves nearer or farther.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why does the dot disappear?
Its image falls on the blind spot, where there are no light-sensing cells.
02Why do we not see a hole in daily life?
The other eye covers the gap and the brain fills in the missing part.
03Where is the blind spot located?
At the point where the optic nerve leaves the retina.
04What cells are found in the retina?
Rods for dim light and cones for colour and bright light.
Take it further
Find the blind spot of a family member and compare whether it is at the same distance for both eyes.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Biology Models Guide
Make the heart, lungs, kidney, eye, cell and more, and explain them well
Science projects
Science Projects for Class 6 to 8
Working models matched to middle-school science topics
Find out more about biology
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.