Where your optic nerve enters your retina, there is a small part of your retina that cannot detect light: a blind spot. Everyone has one. In fact, everyone has two: one in each eye. The two blind spots are in different parts of your field of view, so even if one eye doesn't see something, the other one will. Even when you look at things with one eye, your brain processes things so that they are smoothed out over the blind spot, so you don't notice it. Fortunately, the blind spot is not in the center of your vision, where your vision is sharpest. It's toward the edge of your field of view, and this also makes it harder to notice. You need to focus on something but concentrate on something else: not an easy feat.

The animation below is designed to help you find your blind spot. Proceed as follows:

* Place your face about 30 centimeters (12 inches) from your screen.
* Cover your left eye with your hand.
* With your right eye, stare at the left dot: the one that does not move.
* Even though you are looking at the fixed dot, concentrate on the one that is moving. This is hard!
* After a while, you should see the moving dot disappear. It has entered your blind spot!
* Eventually, the dot will come back again.

Now watch the animation with both eyes to see that we aren't playing a trick on you. The spot doesn't vanish; it just appears to.

You can see the blind spot in your left eye by covering your right eye and focusing on the moving spot while concentrating on the fixed spot.

An apology for having an animation that works best for "right eyed" people: people whose right eye is the stronger of the two. If it's any comfort, the folks that built the page are left eyed too!