How to Find Your Blind Spot

Each of our eyes has a blind spot. It is located near the center of the retina and near where the large optic nerve exits the eye and travels to the brain. This spot is blind because there are no light-sensitive cells there – the space is occupied by nerve fibers converging and entering the optic nerve sheath.

In our daily activities we do not notice the two blind spots because we have binocular vision. The data provided by each eye overlaps with the data provided by the other eye, so no gaps are evident to our brain.

The Basic Experiment

Take a piece of white paper and draw a square near the left side. Make it about one quarter of an inch wide and fill it in with any color.
Now draw a circle three or four inches to the right, also about a quarter of an inch in diameter and filled in with the same color. The square and circle do not have to be geometrically exact.
Hold the paper out in front of you and close your left eye.
Gazing at the square with your right eye, slowly bring the paper closer towards your face.

Although you can see both the square and circle at first, there will be a point where the circle disappears. You have moved it into the blind spot of your right eye. Where the circle should be, there is just white paper. To find your left eye’s blind spot, just repeat the experiment looking through your left eye with your right eye closed.

An Interesting Question

Why can you see white paper when the circle is invisible? Why don’t you see a round piece of whatever is behind the paper – the wall or a window?

Answer: Your brain is smart. It knows you drew the circle on white paper, so it fills in the blank space with the same white. You can confirm your brain’s smartness by repeating this experiment using colored paper. Using blue paper, you will see blue instead of the invisible circle.

A Further Experiment

On a new piece of white paper, draw the same square to the left.
About two inches to the right of the square, draw a filled-in rectangle about one quarter of an inch high and an inch long; then the same small circle a little to the right of the rectangle, then a second rectangle.

Close your left eye and focus with your right eye on the square. As you move the paper closer, the circle will again disappear but the two rectangles will merge. This time your smart brain has filled in the blank space by extending the adjacent rectangles across it.

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