Here is Charles Bonnet as he might appear in a hallucination by a patient who has the disorder which is named after him.
Neurologist Oliver Sacks talks about Charles Bonnet Syndrome, a condition that creates hallucinations of geometric patterns, distorted faces and cartoon images in people who have impaired vision or are blind. These visual deceptions are not "optical illusions" because they’re created directly by the brain. Mr. Sacks repeats an intriguing question: How can the theater of the mind be generated by the machinery of the brain?
Oliver Sacks: What hallucination reveals about our minds
Charles Bonnet Syndrome at Retinal Physician>>