The Charles Bonnet syndrome: 'phantom visual images'.

The Charles Bonnet syndrome is a condition in which individuals experience complex visual hallucinations without demonstrable psychopathology or disturbance of normal consciousness. An analysis of the sixty-four cases described in the literature reveals that the syndrome can occur at any age though it is more common in elderly people. Reduction in vision, due to peripheral eye pathology as well as pathology within the brain, is associated with the syndrome. Individual hallucinatory episodes can last from a few seconds to most of the day. Episodes can occur for periods of time ranging from days to years, with the hallucinations changing both in frequency and in complexity during this time. The hallucinations may be triggered or stopped by a number of factors which may exert their effect through a general arousal mechanism. People, animals, buildings, and scenery are reported most often. These images may appear static, moving in the visual field, or animated. Emotional reaction to the hallucinations may be positive or negative. Several theories have been proposed to account for the hallucinations. This paper highlights the sensory deprivation framework, with particular emphasis on the activity in the visual system after sensory loss that produces patterns of nerve impulses that, in turn, give rise to visual experience.