That it has a pupil! Haha, no 
Sometimes pied birds tend to have 'cracked' or 'split' eyes, which is where parts of the eye are shadowed/black. It can be a little bit to nearly the whole eye. If that's not what you're talking about, then I don't know. But I can say split eyes has nothing to do with how good a bird is
It's like when you have a blue bar you expect it to have bars; it just happens.
Sometimes pied birds tend to have 'cracked' or 'split' eyes, which is where parts of the eye are shadowed/black. It can be a little bit to nearly the whole eye. If that's not what you're talking about, then I don't know. But I can say split eyes has nothing to do with how good a bird is