Background: Charles Bonnet's Syndrome (CBS), characterised by the presence of complex visual hallucinations in psychologically normal people, was considered for a long time to be rare. Systematic research on CBS has been limited. However, it has been realised that CBS occurs frequently in elderly, visually handicapped patients, and we have been able to study the syndrome in a large number of patients.
Methods: After screening 505 visually handicapped patients, 60 were found to meet proposed diagnostic criteria for CBS (generally, the existence of hallucinations without delusions or loss of insightful cognition.) Psychopathological characteristics, personal meaning, and the emotional impact of hallucinations, as well as factors influencing the hallucinations, were analysed.
Findings: Although diagnostic criteria demand merely "partial insight", all patients had full insight into the unreal nature of their hallucinations. Other characteristics varied. In 46 (77%) patients, hallucinations lacked a personal meaning. Sensory deprivation and a low level of arousal seemed to favour the occurrence of hallucinations. CBS caused considerable distress in only 17 (28%) patients. However, all patients were glad to be told that their hallucinations were not due to mental disease. The proper diagnosis had been made in only one of the 16 patients who had consulted a doctor.
Interpretation: Although largely unrecognised in clinical practice, CBS should be considered as a diagnosis in patients who complain of hallucinations and who meet defined diagnostic criteria. There is no proven treatment, but many patients will benefit from reassurance that their hallucinations do not imply mental illness.