Charles Bonnet Syndrome

What is Charles Bonnet syndrome?

Charles Bonnet syndrome (CBS) is a common side-effect of sight loss in which people see things that are not there (visual hallucinations). The hallucinations can be very clear, detailed, and consistent and can happen to people with good mental health. 

We don't know for use how many people in the UK have Charles Bonnet Syndrome, but it is estimated to be hundreds of thousands, with some experts even putting the number as high as one million.

It's named after the Swiss naturalist who first described it and is usually pronounced Charles Bon-nay. 

What causes Charles Bonnet syndrome?

We don't know exactly what causes Charles Bonnet syndrome, but it's more likely if you have severe sight loss or blindness, especially in both eyes. It's more common in older people, when people are socially isolated, and after vision gets worse suddenly. 

Although eyes are the sensors that respond to light, it's the brain that does the seeing. The brain receives information from the eyes and decodes it into the picture we see. If the brain stops receiving information, it can fill in the gaps with its own images.

So it's possible that Charles Bonnet syndrome is similar to the feeling of having a 'phantom limb' that can be experienced by people who lose an arm or a leg.

What are the signs and symptoms of Charles Bonnet syndrome?

Charles Bonnet syndrome hallucinations can be very detailed and much clearer than your everyday vision, and appear suddenly, lasting for a few minutes or sometimes several hours. Although the hallucinations are very vivid, people usually know – or learn to recognise – that what they're seeing is not really there.

Other senses, such as smell, hearing, taste, and touch are not affected. Charles Bonnet syndrome can happen to people with good mental health who have no history of psychiatric problems. 

The kinds of things people see with CBS is thought to fall into two main types:

1. Simple repeated patterns or shapes, such as grids or brickwork patterns.
2. Complex hallucinations of people, objects, and landscapes. These can vary from benign to alarming - for example, some people report seeing ‘snakes crawling out of people’s heads’ others see children in Victorian dress.

Is Charles Bonnet syndrome serious?

Charles Bonnet syndrome can cause huge distress to people who experience it, and can have a big impact on quality of life. It does not mean that you have dementia or a serious mental illness, and the hallucinations may happen less often as time goes on. 

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How is Charles Bonnet syndrome diagnosed?

There isn't a specific test for Charles Bonnet syndrome. You may be asked about your medical history, as well as having an eye test and other tests to rule out other causes of visual hallucinations.

What are the treatments for Charles Bonnet syndrome?

At the moment there is no specific cure for Charles Bonnet syndrome, but it is possible to make it easier to deal with. There may be simple practical things that can help to stop hallucinations when they start, such as changing the lighting or what you're doing at the time. 

Eye movements (moving your eyes from left to right 15 to 30 times, then repeating if needed) can help stop a troubling hallucination. Medications may also help if the hallucinations are distressing.

What can help Charles Bonnet syndrome?

It can be helpful to understand that the hallucinations are a normal result of sight loss and not a sign of mental illness. It may also be helpful to talk to family or friends and to your GP or eye doctor, especially if the hallucinations are getting in the way of day-to-day life. 

What research is there into Charles Bonnet syndrome?

Fight for Sight, together with partners Blind Veterans UK, Esme's Umbrella, and Health and Care Research Wales, is funding two research projects at Cardiff University and University of Oxford to investigate the cause of the visual hallucinations associated with Charles Bonnet Syndrome, with the hope of eventually finding a cure.

One study will investigate the possibility that peripheral (‘side’) vision is more ‘suggestible’ than central vision. The second study will use a special type of MRI scan to measure the levels of chemicals in the visual areas of the brain to see whether they are abnormal in people with Charles Bonnet Syndrome.

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