How does Gaston Leroux use imagery in The Phantom of the Opera?

Leroux gives Erik glowing eyes, which create an eerily, nonhuman picture. His eyes glow in the dark. They are luminous and provide him with the ability to move frrely in the dark.

When Christine and Raoul see Erik's eyes from a distance, he is spying on them. Erik also shoots a pistol in the direction of the eyes, wounding what he believes to be is a cat.