The human eye has a blind spot

The human eye has a blind spot at the area of the retina where the optic nerve leads back into the brain.

The blind spots in each eye are aligned symmetrically so that most of the time, one eye’s field of vision will compensate for the loss of vision in the other. The diagram above shows where the blind spots are located.

To find the eye’s blind spot, you can do the following tests.

In order to find the blind spot of the right eye, it is necessary to close the left eye, focus the right eye on a single point, and see if anything vanishes from vision some 20 degrees right of this point. The following diagram has a set of characters on the left hand side, and black circle on the right. Keeping your head motionless, with the right eye about 3 or 4 times as far from the page as the length of the red line, look at each character in turn, until the black circle vanishes.

This is seriously some trippy stuff!

The opposite idea works in testing the blind spot of the left eye as well. Just do the exact same as the image above, but with the left eye opened and the right eye closed.

Those are the two basic eye tests.

It’s amazing how the brain assumes certain things in our field of vision so accurately despite the fact that the eyes cannot actually see what is there.