We are visiting family in Arizona. Yesterday we all went into the desert, visiting some archaeological sites at Agua Fria Nat. Mon. This morning, Ben had green goop coming out of his left eye. All day I've been wiping off clear or white goop. I don't know whether it's a reaction to dust, an allergic reaction to strange vegetation, or even a scratch on his eye from a cactus. It seems to be lessening, but I'm wondering if I should be worried about it? How do I tell whether we need to see a vet or if it will resolve itself in a couple of days?