While my informant grew up in Los Angeles, my informant’s family is from Yucatan, Mexico and he frequently goes down to visit his grandparents who live on a ranch. He heard this information when he was a child visiting his grandparents. His uncle taught him this:
“If you see a dog poop, you’ll get an infection, like a pimple, in your eye”
My informant says that it comes a lot from the community in Yucatan. He said he did not know why this particular belief existed, but he did say that his uncle liked to tease him.
This belief is playing with the obscene and gross. One disgusting thing leads to another. Dogs are common in many places in the world, so having a dog poop in front of you is not too unlikely. The idea behind the belief is that disgusting things can rub off or effect you if you witness them.