"How, then, am I mad? Hearken! observe how healthily-how calmly i can tell you the whole story."
The narrator describes the old mans eye as being pale blue with a film over it. The old man's eye also is compared to the eye of a vulture. Because of the description that the narrator gives of the old man this is what I imagine that he looks like.
The narrator continues to hear a "heart beat" that is coming from the old mans dead body. This "heart beat" continues to vex him and bug him which leads him to confess to the murder of the old man.