Charles Bonnet syndrome is a cause of complex visual hallucinations. The core features are the occurrence of well formed, vivid, and elaborate visual hallucinations in a partially sighted person who has insight into the unreality of what he or she is seeing. Its prevalence in patients with visual impairment varies from 10% to 15%. To diagnose the condition there should not be features which might lead to an alternative explanation such as psychosis, dementia and intoxication.
The syndrome occurs most commonly in elderly people, probably because of the prevalence of visual impairment in this group. The common conditions leading to the syndrome are age related macular degeneration, glaucoma and cataract. The hallucinations may last from a few seconds to most of the day and may persist for a few days to many years, changing in frequency and complexity. Many patients can voluntarily modify them or make the image disappear if they close their eyes.. The imagery has no personal meaning and is varied and may include groups of people or children, animals, and panoramic countryside scenes.
The condition is named after the Swiss naturalist and philosopher Charles Bonnet. He reported the hallucinations of Charles Lullin, his 89 year old otherwise healthy and cognitively sound grandfather, who was blind owing to cataract and yet vividly saw men, women, birds, and buildings.
There is no definitive treatment for the condition but it is reported that reassurance and explanation that the visions are benign and do not signify mental illness has a powerful therapeutic effect. Hallucinatory activity may terminate spontaneously, on improving visual function or on addressing social isolation. There is no universally effective drug treatment but anticonvulsants may play a limited role.
Charles Bonnett syndrome – elderly people and visual hallucinations – excellent BMJ paper (paywall)
Complex visual hallucinations in the visually impaired: the Charles Bonnet Syndrome.
Charles Bonnett Syndrome – Wikipedia