First published April 2006, updated May 2021

Charles Bonnet Syndrome (CBS) refers to visual pseudo-hallucinations that occur in the elderly with visual impairment. The syndrome is named after the 18th Century Swiss naturalist Charles Bonnet, who described the condition in his own grandfather and which he himself suffered from in his later years1.

Its prevalence has been reported at 10 to 15 per cent and occurs most commonly in the elderly, probably because of the frequency of visual impairment in this age group2. It does not show gender preference and appears later in life at a mean age of 57.5 years3.

The relevance to geriatric medicine is that patients may be incorrectly diagnosed with psychiatric conditions or dementia if their physicians remain unaware to the existence of the syndrome. In this article, we describe the clinical course of the condition.

Risk factors

Advanced age and visual impairment are significant risk factors for CBS along with social isolation, although this has not been confirmed statistically4. Unsurprisingly, common conditions leading to CBS are macular degeneration, glaucoma and cataracts5.

Aetiology

The aetiology of CBS is still largely unknown. It is likely that non-organic factors such as isolation and a contracted social network play a major part in the development of the syndrome2. Burke6 has suggested a neurological basis for these hallucinations, proposing that biochemical and molecular changes cause a loss of sensory input from the visual cortex (deafferentation). This is the phenomenon whereby hyperexcitation develops in neurons when their afferents have been silenced, and is best exemplified in the phantom-pain syndrome. However, it is likely that a combination of factors – visual impairment, social isolation and cerebral dysfunction – contribute to the pathogenesis of CBS3,7.

Clinical features

The hallucinations are vivid, complex and well formed. They frequently have no personal meaning, are recognised as being unreal by the patients and can sometimes be voluntarily terminated by the patient2. Patients report that the hallucinations can last from seconds to hours with varying frequency and intensity3. There are no consistent triggering factors and people, animals or buildings can cause hallucinations9

The course and prognosis of the condition is very variable. The hallucinations are generally well tolerated and benignly regarded by the patient – however, uninformed patients can become anxious as they are unaware of the underlying condition3. Improvement in the hallucinations may result from addressing the underlying visual impairment (e.g. removing a cataract) or when the remaining visual acuity is lost (e.g. progression to total blindness)5.

Management

Treatment of CBS is multi-pronged – physician reassurance, patient education and improving visual acuity comprise some of the options available to clinicians. Pharmacotherapy plays a role in ameliorating the hallucinations but there is only anecdotal evidence available – Batra3 recommended an atypical neuroleptic melperone; Kornreich et al10 cautioned the use of another atypical, risperidone, as it exacerbated the condition; and Fernandez2 found that identical neuroleptics have different effects on the hallucinations and the authors recommend that patients should receive individual treatment for CBS.

Onset

Sudden

Cortical defects

Absent

Visual defects

Present

Visual hallucinations

Present

Intact sensorium

Present

Delusions

Absent

Insight

Present

The significance to the elderly

The significance of CBS lies in the danger that elderly patients might be wrongly diagnosed with psychosis on the basis of their hallucinations5. Such patients might also be reluctant to admit to such symptoms for fear of being labelled as suffering from mental illness. Such misconceptions might also account for low incidence and prevalence figures, and physicians should therefore inquire about visual hallucinations in elderly visually impaired patients. 

Increased awareness amongst physicians and patients of the syndrome will allow earlier recognition and treatment. Although treatment of the visual impairment might ease the symptoms, it is the reassurance that their condition is not a ‘mental health problem’ that brings relief to these patients2,11 Conclusion CBS is an important condition that remains underdiagnosed. The patient described in the case above had well-documented risk factors for developing the condition, namely advanced age and bilateral cataracts. The key clinical feature is the recognition by the patient that the hallucinations are unreal, and this point is valuable is differentiating it from psychosis. Management of CBS is multi-faceted and involves reassurance, education and, where possible, improving visual acuity.

Case study 

A patient presented to the Accident & Emergency department with acute agitation and distressing visual hallucinations. He had a one month history of visual hallucinations, but had previously always maintained insight that they were not real. He had significant visual impairment secondary to bilateral cataracts and the General Practitioner (GP) had diagnosed Charles Bonnet syndrome. The hallucinations were always distressing in nature, and included both animate and inanimate objects. He had recently been diagnosed with depression by his GP and had been started on citalopram a week prior to admission.

He had an abbreviated mental test score of 8/10 and systems examinations were unremarkable. There were no signs suggestive of infection or an acute neurological event that could account for the patient’s symptoms. Blood tests showed hyponatraemia, with a plasma sodium level of 124mmol/L. Computed tomography of the brain showed generalised cerebral atrophy and small vessel disease, but no acute changes. The remaining investigations, including electrocardiogram and chest X-ray, were normal.

Hyponatraemia, being a well-recognised cause of neurological disturbances, was addressed, firstly by discontinuing citalopram (hyponatraemia is a known side-effect of selective serotonin reuptake inhibitors). Together with fluid restriction, the sodium level improved, but the patient continued to experience visual hallucinations irrespective of this, and in the presence of normal remaining blood tests. The hallucinations occurred at a frequency of one every five days, and took a variety of forms.

The patient was then reviewed by an ophthalmologist and underwent surgery for the cataract in the right eye. Following this he remained in hospital for a week, during which he did not report any further visual hallucinations.

References 

  1. Bartlett JEA. A case of organized visual hallucinations in an old man with cataracts and their relation to the phenomena of the phantom limb. Brain 1951; 74: 363–73
  2. Fernandez A, Lichtshein G, Vieweg W. The Charles Bonnet syndrome: A review. Journal of Nervous & Mental Disease 1997; 185(3): 195–200
  3. Batra A, Bartels M, Wormstall H. Therapeutic options in Charles Bonnet syndrome. Acta Psychiatrica Scandinavica 1997; 96(2): 129–33
  4. Teunisse RJ, Cruysberg JR, Hoefnagels WH, et al. Risk indicators for the Charles Bonnet syndrome. Journal of Nervous & Mental Disease 1998; 186(3): 190–2
  5. Jacob A, Prasad S, Boggild M, et al. Charles Bonnet syndrome - elderly people and visual hallucinations. British Medical Journal 2004; 328(7455): 1552–4
  6. Burke W. The neural basis of Charles Bonnet hallucinations: A hypothesis. Journal of Neurology, Neurosurgery & Psychiatry 2002; 73(5): 535–41
  7. Teunisse RJ, Zitman FG, Raes DCM. Clinical evaluation of 14 patients with the Charles Bonnet syndrome (isolated visual hallucinations). Comprehensive Psychiatry 1994; 35: 70–75
  8. Gold K, Rabins PV. Isolated visual hallucinations and the Charles Bonnet syndrome: A review of the literature and presentation of six cases. Comprehensive Psychiatry 1989; 30: 90–98
  9. Schultz G, Melzack R. The Charles Bonnet syndrome: Phantom visual images. Perception 1991; 20: 809–25
  10. Kornreich C, Dan B, Verbanck P, et al. Treating Charles Bonnet syndrome: Understanding inconsistency. Journal of Clinical Psychopharmacology 2000; 20(3): 396
  11. Teunisse RJ, Cruysberg JR, Verbeek A, et al. The Charles Bonnet syndrome: a large prospective study in The Netherlands. British Journal of Psychiatry 1995; 166(2): 254–7