Details like the vulture's eye were simply perfect. Any changes I made just ruined the story. The whole story is rigged so that nobody can change even a single detail of Poe's story without having to change the whole story. That will give you an idea of how important all Poe's images are. Personally I think it's because of the symbolism of the vulture.
Vultures appear when something is going to die.
They circle above victims who are at their weakest point,taking all hope and happiness from them. They feed on dead flesh, not caring how long it has been rotting. They eye of the vulture is predatorial. It fixes on the victim and guides the vulture straight to the decaying flesh. This is the perfect eye for the old man.