It likely has other genetic anomalies that you may not be able to determine yet. I personally would cull, but that's certainly your choice to make. I've also never had to cull, as I just have 3 chickens in the backyard and don't breed. If you are willing to take on the challenge of a bird that requires special care, you can give it a chance, but my guess is that it has other developmental or anatomical problems that may not yet have shown themselves. You will need to make sure it can find food and water and that they are always in the same place. It will be particularly vulnerable to predators, of course. There are threads on blind chickens and how people help them accommodate to their disability, and possibly a few about ducks as well. Try searching the site if you wish to give it a chance.