Blind Spot in Your Vision: Why Do You Have One and Why Can’t You See It?
There’s a blind spot in your vision right now.
In fact, you have one in each eye.
Yet as you look around the room, you probably don't see two black holes or missing patches in your view. Everything appears continuous.
So where has the missing piece gone?
The answer reveals something fascinating about vision: seeing isn't simply a case of your eyes recording the world like a camera. Your eyes collect visual information, but your brain plays an enormous part in creating the picture you actually experience.
And, with a very simple experiment, you can actually find your own blind spot.
Why Is There a Blind Spot in Your Vision?
To understand the blind spot in your vision, we first need to look at the retina.
The retina is the light-sensitive tissue lining the back of the eye. It contains specialised photoreceptors called rods and cones, which respond to light and begin the process that ultimately allows us to see.
But there is one small area of the retina where there are no rods or cones at all.
This is the optic disc.
It's the point where nerve fibres from the retina come together and leave the eye as the optic nerve, carrying visual information towards the brain. Because there are no photoreceptors at the optic disc, light falling on this particular area cannot be detected.
That creates your natural, or physiological, blind spot.
So Why Don't You See a Black Hole?
This is where things become particularly interesting.
You might imagine that having an area of retina that can't detect light would leave an obvious black patch in your vision.
But that's not what you experience.
Part of the reason is that we normally look at the world with two eyes. The blind spots occur in different places in each eye's visual field, so information available to one eye can help where information is absent from the other.
But there's more happening than simply having two eyes.
Your visual system also uses information from the area surrounding the blind spot to create a perceptually continuous scene.
So rather than presenting you with a conspicuous empty hole, your brain constructs a coherent visual experience from the information available to it.
It's a wonderful demonstration that seeing happens not just in the eyes, but through the interaction between the eyes and brain.
Can You Find the Blind Spot in Your Vision?
Now for the fun part.
You can demonstrate your blind spot in your vision yourself.
Try this simple blind-spot experiment
On a computer or tablet, look at these two symbols:
● ✚
1. Cover your LEFT eye.
2. Look directly at the ● with your RIGHT eye.
Keep looking at the dot. Don't look across at the cross.
3. Slowly move your head closer to and further away from the screen.
At a particular distance, something strange should happen:
The ✚ disappears.
Keep moving and it should eventually reappear.
Important: If it doesn't disappear immediately, don't worry. Screen size, viewing distance and the spacing between the symbols all affect the experiment. Try changing your distance slowly while keeping your gaze fixed firmly on the dot.
Where Did the Cross Go?
Obviously, the cross didn't actually disappear from your screen.
Instead, at a particular viewing distance, the image of the cross fell onto the optic disc of your right eye — the area without photoreceptors.
Your eye therefore couldn't detect it.
But perhaps the most fascinating part is what you didn't see.
You didn't necessarily see a black hole where the cross had been.
Instead, the surrounding background appeared to continue across the missing area.
Your visual system effectively dealt with the missing information without drawing your attention to it.
That's why we normally go through our entire day completely unaware that this gap exists.
Is Your Natural Blind Spot the Same as Losing Part of Your Vision?
No — and this distinction is important.
Everyone has a normal physiological blind spot corresponding to the optic disc.
That's very different from developing a new missing, blurred or distorted area of vision.
Changes to the retina, optic nerve or other parts of the visual pathway can produce abnormal visual-field defects. These are not the same thing as the normal blind spot we've demonstrated above.
If you notice a new dark or missing area, sudden change in vision, flashes, a sudden increase in floaters, or a curtain/shadow across your vision, seek prompt professional advice rather than assuming it is your natural blind spot.
Can an Optometrist Measure Your Blind Spot?
Yes.
During certain types of visual-field testing, small targets are presented at different locations while you look at a central point.
Your responses allow a map of your visual field to be produced.
The normal physiological blind spot can be demonstrated because stimuli presented in that particular location aren't detected. Formal visual-field testing can also identify other areas where visual sensitivity is reduced or absent.
Visual-field assessment can therefore be an important part of investigating and monitoring certain eye conditions.
Your Eyes Aren't Cameras
It's tempting to think that vision works like a camera:
Light enters → an image is recorded → you see it.
The reality is considerably more interesting.
Your retina is constantly converting light into neural signals. Those signals travel through complex visual pathways to the brain, where information is processed and interpreted.
The blind spot in your vision gives us a particularly simple demonstration of this.
There is genuinely an area in each eye where no photoreceptors detect the image falling upon it.
Yet you normally have absolutely no idea it's there.
What you see isn't simply what your eyes receive — it's the visual experience your brain creates from the information available to it.
And that's what makes the science of seeing so fascinating.
More from our Science of Seeing series
If you enjoyed discovering the blind spot in your vision, explore more of the everyday mysteries behind how we see.
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