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Charles Bonnet syndrome—elderly people and visual hallucinations
Anu Jacob, research fellow, Sanjeev Prasad, [...], and Sanjeev Chandratre, consultant

When a patient presents with vivid visual hallucinations, a doctor probably considers common diagnoses such as delirium, dementia, psychoses, or a drug related condition. Charles Bonnet syndrome, however, is a condition characterised by visual hallucinations alongside deteriorating vision, usually in elderly people.1 The correct diagnosis of this distressing but not uncommon condition is of utmost importance, considering the serious implications of the alternative diagnoses.
Case report
Neighbours brought an 87 year old white widower—who lived alone in a flat—to the medical assessment unit of a district general hospital. They were concerned that he was becoming demented. Apparently he had reported seeing people and animals in his house—including bears and Highland cattle. He verified these statements and said he had been seeing them for the previous six weeks. He had also often seen swarms of flies and blue fish darting across the room.

He knew that these visions were not real and they didn't bother him much, but he thought he might be losing his mind. The visions lasted for minutes to hours, and the cattle used to stare at him while quietly munching away at the grass. The visions tended to occur more in the evenings before he switched on the lights.

His medical problems included chronic lymphatic leukaemia, which had been in remission for the past five years. He was registered blind and had been diagnosed as having gross bilateral macular degeneration. He had never had hallucinations before. He also had chronic obstructive airways disease and essential hypertension. He had had no other neurological illness and no mental health problems. He did not drink alcohol or smoke. He had been taking oxprenolol for hypertension for the past 10 years. He had no family history of note.

His cognitive examination was normal for his age, after the loss of vision was taken into account. His visual acuity in both eyes was 1/60 with loss of central field. Fundi showed macular degeneration. The rest of the neurological examination was normal.

Detailed investigations (including a full blood count; glucose; electrolytes; and tests for renal hepatic and thyroid function, vitamin B-12, and folate levels) yielded normal results. Detailed psychiatric assessment did not pinpoint a cause and suggested more detailed investigations for delirium. As a metabolic and infection screen was normal and he was otherwise well oriented, delirium did not seem a likely diagnosis. Electroencephalography and magnetic resonance imaging showed no important abnormalities. No diagnosis was apparent even after a week of inpatient tests and ward rounds. An early dementia seemed to be the obvious explanation—until we did a literature search.........................................................

Though no universally approved diagnostic criteria for the syndrome exist, the core features are the occurrence of well formed, vivid, elaborate, and often stereotyped visual hallucinations in a partially sighted person who has insight into the unreality of what he or she is seeing. There should not be any feature of psychosis, impaired sensorium, dementia, intoxication, metabolic derangement, or focal neurological illness.3-5 Charles Bonnet 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, followed by glaucoma and cataract. These hallucinations, which are always outside the body, may last from a few seconds to most of the day. They may persist for a few days to many years, changing in frequency and complexity. They have no personal meaning, and many patients can voluntarily modify them or make the image disappear if they close their eyes. The imagery is varied and may include groups of people or children, animals, and panoramic countryside scenes.