As an artist - especially a portrait artist - you have to become very familiar with the human skull. It is the foundation of the face. If you are ever going to accurately capture someone's likeness, you need to understand what lies beneath their skin.
The ray of light peeking through the crack creates a blinding effect on the subject. The light is so bright that it blinds her vision, covering her eyes in the photo. The black and white filter makes the ray of light even more bright.