What is the meaning and purpose of the simile "the room was black as pitch" in Poe's story "The Tell-Tale Heart"?

Pitch is the color of tar, which is a deep dark black.  The  full lines in which this simile occurs read:  His room was as black as pitch with the thick darkness (for the shutters were close fastened through fear of robbers), and so I knew that he could not see the opening of the door, and I kept pushing it on steadily, steadily.

"Pitch," alludes to the lack of light in the room in a literal sense.  In the gothic sense, pitch is also often used in reference to midnight, to things satanic, and to evil in general.  By employing the similie in this way, Poe brings a sense of both physical and emotional doom to the story.