Look at the red cross on the left with your right eye, closing your left eye. Move your head slowly closer to the image, then further away. At a certain distance the blue dot on the right will disappear. That’s your blind spot!
Your eyes have three types of color receptors: red, green, and blue. After-images appear when you stare at a particular color for too long and those receptors get tired. So stare at the white dot at the center of this image without blinking.
Most people have a dominant eye. To find out which is yours, make a triangle between your thumbs and forefingers. With both eyes open, look at an object several feet away, centering it inside the triangle.