In my side vision when I look straight ahead or sleep on my side in my far side vision when the lights are off it looks like something white is moving or dancing in my side vision, but with the lights on and looking straight ahead and say to the right of me is a bright wall, it looks like something dark is dancing or moving around in my side vision. What could this be? it generally goes away when I blink but it comes back when I keep my eyes open for a while.