Blind comet goldfish?

It sounds to me as if has injured it awhile ago and has gotten use to it. i wouldn't have it be put in another tank though with other fish they will most likely get aggressive to it and end up killing it. It does not mean it is close to the end of it's lifespan but it does meaen you should keep watching it when it is feeding time and make sure it eats(as you are doing). Good luck!