What do you think the author means by the term "evil eye"? Why do you think the narrator of the story is so disturbed by the old man's eye? And why...

In "The Tell-Tale Heart," the narrator and the old man appear to live together because the narrator is a caretaker for the old man.  Either they are family members, or the narrator works for the old man.  The narrator appears to be so vexed by the old man's eye because the old man probably "sees" who the narrator really is--one who has gone mad.  At the beginning of the story, the narrator tries to convince the reader that he is not mad and that he just suffers from acute senses.  However, as the plot unfolds, the reader sees that the narrator is in fact mad as he fixates on the old man's eye and plots to kill him to rid the house of the eye.  The old man is not an active character in the story, so the reader cannot confirm whether or not he knows about the narrator's mental instability, but we can assume that he does know given that they live together.  The narrator is likely also aware that the old man suspects his insanity, and the eye "sees" through the facade that the narrator attempts to build to hide his true identity.