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Charles Bonnet Syndrome (CBS)

What is Charles Bonnet Syndrome?

Charles Bonnet Syndrome (CBS) is characterised by visual hallucinations in people affected by sight loss from any cause, including inherited eye disorders. People of any age with sight loss may be affected by CBS but it typically affects older people.

The hallucinations experienced are different in each patient. Some describe simple shapes like lines and dots, coloured blobs and geometrical patterns. Others have experienced more complex hallucinations involving faces (sometimes distorted or gargoyle-like), people (young or old) often in period costume or whole vivid scenes. The emotions that patients experience with these hallucinations can be one of indifference, enjoyment or fear.

CBS is estimated to affect 0.4-30% of people with sight loss[1], though it is considered to be underreported due to patients’ fears of being categorised as mentally ill, and a relative lack of awareness amongst the medical profession.[2]

Video explaining about Charles Bonnet Syndrome

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Normally, vision is formed through a multi-step process. Light entering into the eye is first detected by specialised cells in the retina called photoreceptors. These cells convert light into electrical signals which is then transmitted to the visual processing part of the brain (visual cortex) via the optic nerve to generate an image (what we see).

A microscopic view of the cells in the retina. The cone-shaped and rod-shaped photoreceptors are situated deepest and supported by the RPE cells. Other cells above the photoreceptors are responsible for transmitting electrical signals to the brain to generate vision.
Incoming light is transformed into electrical signals in the retina which is then transmitted to the brain for further processing to generate an image

If the retina or any part of this pathway is damaged, the stream of electrical impulses to the visual cortex is reduced. It is believed that in CBS, the brain cells in the visual cortex responds paradoxically by firing more signals, causing visual hallucinations.[3] The image of the hallucination depends on which area of visual cortex is stimulated. For example, a stimulation in an area specialised for faces will cause the hallucination to have faces.

It is important to remember that CBS hallucinations only involve sight. If other senses (hearing, smelling, tasting or touching) are involved as well then it is not considered to be CBS. Patients with CBS are also aware that the visual hallucinations experienced are not real compared to hallucinations from other causes. [1]

In a recent publication in the British Journal of Ophthalmology, the largest series of 13 paediatric and young adult patients were reported with CBS, nearly 70% were male and the median age of onset was 11 years (range 9–19). Over 60% of these patients were diagnosed with an inherited retinal dystrophy (IRD); the most prevalent cause was Stargardt disease, which is the most common childhood macular dystrophy. Other IRDs included Usher syndrome, Batten disease and Leber congenital amaurosis.

The remaining cases were affected with congenital eye disorders including microphthalmiaocular coloboma, and an inherited optic nerve disorder (hereditary optic neuropathy) that does not have a genetic diagnosis yet. This study provides evidence that CBS occurs in children and the whole multidisciplinary team must raise awareness by actively asking/informing patients or families about symptoms.

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Although several medications have been trialled, there are still currently no effective treatments for CBS.[4] However, there are certain methods to help alleviate symptoms and the anxiety associated with CBS.

1) Coping mechanisms

Patients have found the following strategies helpful in minimising or eliminating the visual hallucinations:

  • Look from right to left once every 15 seconds without moving your head when the hallucination start; May need to be repeated four or five times to have an effect (do not go beyond five times if not beneficial)
  • Blink your eyes once or twice
  • Try to touch the hallucination
  • Stare straight at the hallucination
  • Turn your head to alternative sides, then move the head towards each shoulder in turn
  • Walk around the room or to another room
  • Shine a torch from below your chin in front of (not into) your eyes
  • Change the light level in your room, or the activity you are doing

2) Education

CBS patients often experience stress and anxiety, which are linked to the uncertainty over the origin and meaning of the hallucinations, especially if they have not been informed about this potential complication of their sight loss previously.[5]

Therefore, we believe it is important to raise the awareness of CBS among patients, relatives and healthcare professionals. By informing patients and following up with coping strategies can have a positive impact on patients’ quality of life.

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Current research

1) National Institute for Health Research (NIHR) SHAPED (Study of HAllucinations in Parkinson’s disease, Eye disease, and Dementia) programme

This research is currently underway to inform NHS practice and policy in relation to visual hallucinations and produce sets of guidelines for clinicians, patients and carers.

2) Transcranial Direct Current Stimulation (TDCS)

As it is widely believed that visual hallucinations in CBS stem from the hyperactivity of brain cells in the visual cortex, TDCS aims to minimise or eliminate these hallucinations by modulating this area of the brain. It is a non-invasive method where small electrodes are placed on the scalp and the stimulation is targeted at specific areas of the visual cortex with hyperactivity.

3) CBS in children

We know there is consistent under-reporting of CBS symptoms and difficulty with case ascertainment in the paediatric population, which is a shortcoming of current ophthalmology services. To address this, we are conducting a prospective study to try to ascertain the prevalence of CBS in children across the UK with the support of the British and Irish Orthoptic Society and the Thomas Pocklington Trust. Further research into CBS is required in order to gain a deeper understanding of the cause and how best to manage symptoms. 

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Further information and support

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  1.  Pang L. Hallucinations Experienced by Visually Impaired: Charles Bonnet Syndrome. Optom Vis Sci. 2016;93(12):1466-1478.
  2.  Jurisic D, Sesar I, Cavar I, Sesar A, Zivkovic M, Curkovic M. Hallucinatory experiences in visually impaired individuals: Charles Bonnet syndrome – implications for research and clinical practice. Psychiatr Danub. 2018;30(2):122-128.
  3.  Painter DR, Dwyer MF, Kamke MR, Mattingley JB. Stimulus-Driven Cortical Hyperexcitability in Individuals with Charles Bonnet Hallucinations. Curr Biol. 2018;28(21):3475-3480.e3473
  4.  Vukicevic M, Fitzmaurice K. Butterflies and black lacy patterns: the prevalence and characteristics of Charles Bonnet hallucinations in an Australian population. Clin Exp Ophthalmol. 2008;36(7):659-665
  5.  Cox TM, ffytche DH. Negative outcome Charles Bonnet syndrome. Br J Ophthalmol. 2014;98(9):1236-1239

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Updated on November 30, 2020
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