Answer:
The more there is the less you see.
I always have to work with something in my eye.
Cold head and feet; round as a ball; always turning around myself.
You shoot me but I don't die. You hang me but I don't die. What am I?
I am not alive but I grow I don't have lungs but I need air I don't have a mouth but water kills me. What am I?
Who makes it, has no need of it. Who buys it, has no use for it. Who uses it, can't see it. What is it?