Visual hallucinations and the Charles Bonnet syndrome.

After dividing clinicians for almost 70 years, Charles Bonnet syndrome has reached an impasse. Defined by a neurologist in the 1930s, the syndrome was intended to eponymize the association of visual hallucinations with age, but evolved into one describing their association with eye disease or, more recently, an etiologically neutral phenomenologic description. Each tradition has its merits but none has defined a specific clinical entity or accounted for visual hallucinations across the spectrum of associated clinical conditions. Recent insights into the neurobiology of vision have shed new light on the problem. Viewed from a neuro-phenomenologic perspective, clinical evidence reveals two distinct hallucination syndromes: one directly related to visual system pathology, the other to pathology in the brainstem or ascending neurotransmitter pathways. The implication is of two independent but interacting pathophysiologic mechanisms and of a need to reassess the classification and management of this common psychopathologic symptom.