Eye Tests That Look Like Magic
Human eyes have a blind spot where the optic nerve exits the back of the eye. This area has no light receptors because the nerve is in the way. You can find your blind spot with this test. Look at the red cross on the left with your right eye. Closing your left eye, move your head slowly closer and further away.
Oh...that's so weird.
At a certain distance, the blue dot on the right will disappear. Pause if you need to. You've just found your blind spot!
Stare at the white dot in the center of the image and try not to blink. Your eyes have three types of cones, or color receptors—red, green, and blue. After-images appear when you stare at a particular color for too long and those color receptors get tired. So when you suddenly switch to looking at a black-and-white image, those tired receptors aren't working as well. This leaves an after-image of the reverse colors.
See Your Veins
Blood vessels and veins feed the photosensitive cells in your eye to keep them alive. These blood vessels cast shadows on your retina. Here's how you can see those veins. Poke a small hole in a Post-it note or piece of paper; hold it against a bright white background, like your computer screen. Look through the hole while shaking the Post-it slightly—you should see a shadowy network of lines, sort of like the veins of a leaf. These are the veins in your eye.
Most people have a dominant eye, meaning that one eye gives more priority information than the other. Eighty percent of people are right-eye dominant. See which is your dominant eye. Make a triangle between your thumbs and forefingers. With both eyes open, look at an object several feet away. Center the object inside the triangle. Close one eye, and then the other. Your dominant eye will look like this. And your non-dominant eye will look like this. It's almost...visionary.
See what "eye" did there?