teded:

Have you ever noticed something swimming in your field of vision? It may look like a tiny worm or a transparent blob, and whenever you try to get a closer look, it disappears, only to reappear as soon as you shift your glance. But don’t go rinsing out your eyes!

What you are seeing is a common phenomenon known as a floater. Floaters are tiny objects that cast shadows on the retina, the light-sensitive tissue at the back of your eye. They might be bits of tissue, red blood cells, or clumps of protein that are suspended within the vitreous humor, the gel-like liquid that fills the inside of your eye. As a result, floaters drift along with your eye movements,and seem to bounce a little when your eye stops.

To learn more about floaters, watch the TED-Ed Lesson What are those floaty things in your eye? - Michael Mauser

Animation by Reflective Films