Blind Spot Test
Make a dot vanish with one eye closed and discover the natural blind spot every eye has.
Every healthy eye has a small area in its field of vision where it sees nothing at all. This physiological blind spot is caused by the optic disc, the place at the back of the eye where the optic nerve and blood vessels leave the eyeball. There are no light-sensitive cells (photoreceptors) at this spot, so any image that falls on it is simply not detected. You never notice it in daily life because the other eye covers the gap and the brain fills in the missing area with the surrounding pattern.
This demonstration uses the classic cross and dot. You close your left eye, look steadily at the cross with your right eye and slowly move closer to the screen. At a certain distance, typically around 25-35 cm depending on screen size, the dot falls exactly on your blind spot and vanishes, while the background seems to continue seamlessly. Move a little closer or further and it reappears. You can repeat it for the other eye by swapping which eye is closed and looking at the dot instead.
It is an educational experiment that shows how vision works and how much the brain contributes to what we see. It is not a test for disease, and it cannot detect abnormal blind spots (scotomas) caused by conditions such as glaucoma; those need formal visual field testing by an eye professional.
How to use
- Sit square to the screen with your face about 50 cm away and the cross directly in front of your right eye.
- Close or cover your left eye.
- Look steadily at the cross with your right eye; do not look at the dot, just be aware of it.
- Move your head slowly towards the screen, keeping your gaze on the cross.
- Stop when the dot disappears; then move slightly closer or further and watch it come back.
- To test the left eye, close the right eye and fixate the dot; the cross will vanish at a similar distance.
Reading your result
If the dot disappeared at some distance and the empty area looked filled in with the background, your blind spot behaved normally. This is expected in every healthy eye. If you could not make it disappear, the most common reasons are that your gaze drifted towards the dot, you moved too fast, or you were testing the wrong eye.
This experiment cannot tell whether your blind spot is larger than normal or whether you have other gaps in your vision. If you notice areas of missing vision in everyday life, bump into things on one side, or have a family history of glaucoma, book a full eye examination with visual field testing.
Caution: Educational demonstration only, not a diagnostic test. New missing areas in your vision, a shadow or curtain, or sudden loss of sight need urgent medical attention.
Frequently asked questions
Why don't I see my blind spot normally?
The two eyes' blind spots fall on different parts of the scene, so each eye covers the other's gap. Even with one eye closed, the brain fills in the area using the surrounding colours and patterns.
Is a blind spot a sign of disease?
No, the natural blind spot is present in everyone. Only additional or enlarged blind areas, found during proper visual field testing, may indicate disease.
Where exactly is the blind spot?
It lies about 15 degrees to the outer (temple) side of the point you are looking at, slightly below the horizontal, in each eye.