I think closing our eyes will affect our balance if we are not blind guys. But for those born with blindness, they have learned to keep balance by other senses. Usually all kinds of our feelings work together to keep the balance of our body, but when we lose one of them, our body will learn to keep balance by the rest of the senses. When we have our eyes open, we can adjust our body against a fixed position to correct our movements, but we often do this unconsciously. When you close our eyes, we need to adapt to the condition for a long time before we can correct your position with eyes closed, so we may lose the balance.