The video above shows how to trick your eyes into showing what it hides from you - the veins in your eye.
Because of an effect called Sensory Adaptation, our senses become desensitized to stimulus after a while. It explains why a strong scent disappears after a while, or how ambient sound don't usually bother us. The same happens with the veins in our eye - the veins actually cast shadows in our retina, but we barely notice it.
The blind spot is a part of your field of vision that can't see. We usually don't notice it because the brains fill the spot with information. The center of your field of vision, called the macula, has the most concentration of retinal cells. In the picture below, the yellow spot is the blind spot, while the red spot (not the shadowy part) is the macula. The image also shows how the veins don't go directly to the macula, preventing you from seeing the veins directly.
|Yep, that's an eye.|
This video shows how to see the veins in your eye. To do so, find an object with a hole (you can make one with your fingers) and a source of white light. Rapidly strobe your eyes with light using the object. You might find it creepy that you can see web-like veins in your vision.
*Image from Wikipedia