Charles Bonnet Syndrome

What is Charles Bonnet Syndrome?

Charles Bonnet Syndrome (CBS) is a condition where individuals experience visual hallucinations which can be vivid and sometimes frightening.

It is often experienced by those with deteriorating vision and is more common in older people, probably as a result of age related sight impairment.

Diagnosis

• Many sufferers do not report these visual hallucinations, fearing that they indicate conditions such as dementia
• Some health professionals may not be aware of the condition
• CBS is usually diagnosed when those experiencing visual hallucinations also have the capacity to understand that the visions are not real
• It has been found that when sufferers discuss the condition, and understand the likely cause, the hallucinations reduce

Causes

CBS is thought to occur as a result of the brain not receiving as much visual information as it is used to and subsequently inventing its own images, either using old images or producing new, unrealistic images. The images often occur when people are at rest and doing little and the images may go if the individual speaks aloud or moves their eyes or body. Sadly, this remedy does not help everyone.

Symptoms

• These can last from a few seconds to many hours, over a few days to many years
• No two cases are the same
• Images can be extremely complex and may have no meaning to the individual
• Image frequency and complexity can change over time
• Common visions are groups of children, animals and countryside scenes although some people see patterns and lines

How can these hallucinations be explained?

After visual signals leave the eye they pass to the back of the brain (the occipital lobe) to the primary visual receiving area, called V1. Here every point in our field of view has a corresponding set of brain cells which, taken together, form a complete map of our visual world.

From V1 the signals are relayed to a series of map-like areas, each specialised for a different aspect of seeing. There is an area specialised for movement, an area specialised for colour, several for faces, one for landscapes and so forth.

Recent brain scanning studies have shown what happens in the brains of CBS patients while they hallucinate. The answer turns out to be surprisingly simple. The colour area becomes active during hallucinations of colours, the object area becomes active during hallucinations of objects, one or other of the face areas becomes active during hallucinations of faces and so forth.

Such studies help explain some of the features of the CBS. With our eyes open, the visual brain expects to receive and process a flood of complex electrical signals. Through eye disease or a break in the visual pathways, what was once a flood becomes little more than a stream, leaving an intact cerebral machine with little to do. The idle visual brain cells, bored with waiting for an appropriate trigger, begin to fire at will. If such spontaneous firing occurs in the colour area, patients experience hallucinations of colour; if in the object area, they experience those of an object and so forth. After a time, the visual brain readjusts to its new level of stimulation from the eye and the spontaneous firing diminishes, explaining why, for many CBS patients, the hallucinations gradually decrease in frequency over time.

(With acknowledgements to Dr Dominic ffytche, The Institute of Psychiatry, London for the section above 'How can these hallucinations be explained?')

Visual hallucinations can cause difficulty in moving around. A KAB Mobility Officer should be able to help. Contact your local KAB Rehabilitation Team to discuss any concerns you may have.

For more information, call our helpline on 01622 691357.

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