Charles Bonnet Syndrome (CBS)
- What is Charles Bonnet Syndrome?
- Current research in Charles Bonnet Syndrome
- Further information and support
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, 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.
- Video on Charles Bonnet Syndrome by the Macular Society
- Information on Charles Bonnet Syndrome by the Royal National Institute of Blind People (RNIB)
- Information on Charles Bonnet Syndrome by the NHS
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).
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. 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. 
Any condition leading to sight loss may cause CBS. Here are some of the more common ones:
- Age-related macular degeneration (AMD)
- Diabetic eye disease
Although several medications have been trialled, there are still currently no effective treatments for CBS. However, there are certain methods to help alleviate symptoms and the anxiety associated with CBS.
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
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.
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.
Current research in Charles Bonnet Syndrome
- 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.
- 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.
Further information and support
Credit: Arthur Ellis, Rob Bidder
- Potts J. http://www.charlesbonnetsyndrome.uk/the-charles-bonnet-syndrome-leaflet.pdf. Accessed 13 November 2019.
- Pang L. Hallucinations Experienced by Visually Impaired: Charles Bonnet Syndrome. Optom Vis Sci. 2016;93(12):1466-1478.
- 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.
- 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
- 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.
- Cox TM, ffytche DH. Negative outcome Charles Bonnet syndrome. Br J Ophthalmol. 2014;98(9):1236-1239