Charles Bonnet syndrome—elderly people and visual hallucinations

Charles Bonnet syndrome—elderly people and visual hallucinations

Anu Jacob, research fellow1, Sanjeev Prasad2, Mike Boggild, consultant neurologist3, Sanjeev Chandratre, consultant4

1 Department of Neurosciences, University of Liverpool, Liverpool L9 7LJ, 2 Care of the Elderly, Calderdale Royal Hospital, Halifax HX3 0PW, 3 Walton Centre for Neurology and Neurosurgery, Liverpool L9 7LJ, 4 Care of the Elderly, Calderdale Royal Hospital, Halifax HX3 0PW

Correspondence to: A Jacob


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.


Differential diagnosis of visual hallucinations

Visual hallucination is defined as a perception of an external object when no such object is present. Hallucinations are different from illusions, in which real objects are misinterpreted. Visual hallucinations can occur in various medical, neurological, ocular, and psychiatric disorders and drug induced states. They may relate to anomalies in almost any part of the visual pathway.

Classification of visual hallucinations

Visual hallucinations can be classified as simple or complex. The simple type includes photopsia (flashes of light), lines or patterns (like fortification spectra, zigzags, or circles). They may be multicoloured. Simple hallucinations may occur in ocular disease such as vitreous detachment or in conditions such as optic neuritis, migraine, occipital lobe seizures, occipital lobe tumours, or other structural lesions.

Complex visual hallucinations, however, are usually well formed and relatively stereotyped and often involve animals and figures in bright colours and dramatic settings. The aetiologies vary and include delirium tremens, dementias, Parkinson’s disease, complex partial seizures, misuse of recreational drugs, schizophrenia, and uncommon conditions such as peduncular, hypnogogic, and hypnopompic hallucinations, migraine coma, and “Alice in Wonderland” syndrome.2

Charles Bonnet syndrome

Charles Bonnet syndrome is a less frequently diagnosed but rather common cause of complex visual hallucination. Its prevalence in patients with visual impairment varies from 10% to 15%.1 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.1 3

Diagnostic criteria and clinical featuresThough 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.35 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, 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.1 3 5


Naturalist and philosopher Charles Bonnet described the condition in 1760


The syndrome can occur in people with normal vision.6 Some have argued that diagnosis of the syndrome does not exclude or require eye disease or brain lesions and that it could even be due to lesions that are not associated with the visual system.5 Reduced or absent stimulation of the visual system (deafferentation hypothesis) leading to increased excitability of the visual cortex is one of the hypotheses.1 7

Course, prognosis, and treatment

The course, prognosis, and treatment vary with the nature of the visual dysfunction. Removal of a cataract or recovery of vision leads to improvement. Other patients find relief when the eye disease progresses to total blindness.8 Some have suggested that the syndrome can even be an indication of early dementia9; this hypothesis needs to be validated. Treatments with drugs remain unsatisfactory, with only anecdotal evidence for the efficacy of atypical antipsychotics and anticonvulsants.1 Non-pharmacological interventions, such as increasing the lighting at home and reducing social isolation by encouraging interpersonal contact, are helpful.1

Clinical correlate

Our patient provides a classic example of Charles Bonnet syndrome. The clinical scenario and the nature of hallucinations are typical. The possibility of oxprenolol causing hallucination was remote as he had been taking the drug for 10 years whereas the hallucinations had been present for only a few weeks. Timely diagnosis and explanation, along with reassurance about the relatively benign nature of the condition, provided immeasurable relief. He still gets occasional hallucinations but considers them as “one of those things you have to put up with.”


As well as being common in partially sighted people, Charles Bonnet syndrome occurs in 1.85-3.5% of psychogeriatric patients who have been referred to psychiatrists by adult physicians, general practitioners, and ophthalmologists for visual hallucinations.1 10 11

Doctors are unfamiliar with the syndrome as a possible diagnosis.1 12 “Near misses” have been reported, in which patients were almost confined to mental health institutions.13 Given the prevalence of partial visual impairment, the number of people in the community, especially elderly people, who do not report the symptoms for fear of being labelled as mentally unwell or demented must be substantial. Clinicians must therefore be aware and ask elderly people with visual impairment whether they have hallucinations. Firm reassurance that the syndrome is not related to mental illness is in itself a major relief to an elderly person burdened already with failing vision, social isolation, and other medical problems.

Not all elderly people presenting with visual hallucinations have dementia

Contributors: AJ collected the data, did the literature survey, and wrote the paper; he is the principal author and is the guarantor. SP collected the data and gave advice. SC designed the study, gave clinical supervision and advice, and helped to write the paper. MB gave advice and helped to write the paper.

Funding: None.

Competing interests: None declared.


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