The third eye raises the perception of other realms, offers a sense of cosmic consciousness and produces knowledge and wisdom. In the book 'The Key to Theosophy', Helena P. Blavatsky talks about the subject, and reveals that it is directly related to the pineal gland. Presumably, human beings had a real third eye, with legendary functions and abilities. But over time, it atrophied due to the desecration and decay of our divine origin. It's as if it progressively diminished, becoming our pineal gland.