An aura being a visual representation of this energy, created by the sight centre of the brain. This appears to be the only logical explanation for auric sight. Physical and non-physical sight are very closely related. They are both forms of perception that allow our brains to perceive energy, of one type or another, as a sight picture.
Eyes receive light - light being a type of energy.
Eyes focus light energy onto light sensitive nerve tissue at the back of the eye, connected to the optic nerve. Basically, this light sensitive tissue changes focussed light energy into a stream of complex electrical signals. These signals are passed, via the optic nerve, to the sight centre of the brain. The brain then interprets these signals into a rich visual picture - what we call normal sight. The brow centre receives a more subtle type of energy than light.