Perhaps, in a flock of ducks; I know nothing of ducks. Probably, or especially, in a flock of chickens, but I still contend that blindness from birth cannot be considered compromised health, by any stretch of the imagination.All the human individuals that you mentioned survived because that the human society ( most of them!) except and help the ones that don't have the fortune of good health. I think, and know that in the ducks flock it will be the last in everything and will be boolied continuously with no chance to defend itself.