I've been hit in my sunglasses while out on the backroads either riding or commuting, I never go cycling without my sunglasses. Sometime though if it's real dusty, I can get stuff in my eyes too, like MJ says, you can flush it out with your water bottle although you might want to stop cycling first and do it on the side of the road... lest you ride right into oncoming traffic or something horrible like that!

Jay