After i've been snowboarding for a few hours, I have the dark spots develop in my vision.

It's more of a pattern of spots that move from the outside of a blob and dissapear in the center, kind of like things going into a whirlpool. This dark pattern is about the size of two fists held togethere in front of my face. It's completely symmetrical, horizontally and vertically.

I do wear yellow ski goggles, so I think I should be protected from the sun, but I still get these dark spots in my vision.

Very strange. Anyone know if this is harmfull, or just wierd?