Harry's nearly 73 and his eyesight isn't what it was. But psychologicallyhe's completely normal. So why is he seeing people, buildings, and shrubs that aren't really there?
The answer has nothing to do with schizophrenia, LSD, or any of the usual causes of hallucinations. Harry's plight is due to a little known--and surprisingly common--condition called Charles Bonnet Syndrome. People with CBS are mentally sound in every way--except they occasionally see things that don't exist.
In a study of elderly patients with poor vision, Dutch scientists found that one in seven had recently hallucinated. Most visions were rather mundane--human faces, usually of strangers, were most common. But occasionally they verged on the weird or frightening. One woman reported seeing humanoid creatures dressed in tree branches.
If CBS sufferers are psychologically normal, where do these images come from? Sensory deprivation is probably a key factor: The eyesight of most patients is less than a third of normal. "People in sensory deprivation tanks start hallucinating after a couple of hours in isolation," notes Robert Teunisse, M.D., of University Hospital Nijmegen in the Netherlands. Something similar might occur in CBS patients.
