Charles Bonnet syndrome

Charles Bonnet syndrome

Charles Bonnet syndrome (CBS) is a common condition among people who have lost their sight. It causes people who have lost a lot of vision to see things that aren't really there, known as visual hallucinations.

CBS can be distressing, but the hallucinations are usually not permanent. Many people experience hallucinations for a year to eighteen months before they become a lot less frequent.

People who have CBS may have lost a lot of their vision from an eye condition, such as age-related macular degeneration, cataract, glaucoma or diabetic eye disease. Many of these conditions are more common in older people so many people who have CBS are older. However, anyone of any age, including children, may develop this condition as any eye condition that causes sight loss can trigger CBS.

There are thought to be more than 100,000 cases of CBS in the UK. Some research suggests that up to 60 per cent of individuals who are experiencing serious sight loss may develop it.

Origins of the name CBS

Charles Bonnet syndrome is named after a Swiss philosopher and writer who lived about 250 years ago. Charles Bonnet wrote about his grandfather's experiences after his grandfather lost his sight to cataracts and began having 'visions' - he could see patterns, people, birds and buildings, which were not really there.

Causes of CBS

The main cause of CBS is loss of vision and how your brain reacts to this loss. The exact way loss of sight leads to hallucinations isn't really known, but research is slowly revealing more about how the eye and the brain work together.

Current research seems to suggest that, when you are seeing real things around you, the information received from your eyes actually stops the brain from creating its own pictures. When you lose your sight, however, your brain is not receiving as much information from your eyes as it used to. Your brain can sometimes fill in these gaps by releasing new fantasy pictures, patterns or old pictures that it has stored. When this occurs, you experience these images stored in your brain as hallucinations. CBS tends to begin in the weeks and months following a deterioration in your sight.

How you know if you have CBS

"I always thought that seeing things was a sign of mental health problems."

If you have lost some sight to a condition like macular degeneration or glaucoma and you start to hallucinate or see things that aren't really there, then you may have CBS.

There isn't one test that your doctor can do to find out whether you have CBS or not. Usually, they try to rule out other causes of hallucinations by talking with you and in some cases doing tests. Your doctor will try and rule out the other causes of hallucinations, like mental health problems, Alzheimer's and other conditions. If there are no signs of these other conditions and you have lost sight, then it is probable that CBS is the cause of your hallucinations.

It is normal to be worried, confused or frightened when you see things that are not really there. Until you know what's happening, you may be concerned that seeing things is a sign of a mental health problem, or you might think you have Alzheimer's disease. However, it is important to remember that CBS is caused by sight loss and not by any other health problem.

If the hallucinations cause you to feel anxious, you may also be inclined to keep quiet about the things you are seeing. However, even though there is no cure for CBS, letting people know that you have this problem or talking about it may offer you some peace of mind.

There are other medical problems, such as Parkinson's disease, Alzheimer's disease, strokes, serious mental illness and other brain conditions, which affect the part of the brain concerned with seeing and these conditions may cause some people to have hallucinations. It is important to remember that having CBS does not mean you're more likely to develop any of these other conditions. Sometimes, if you have one of these conditions as well as CBS because of sight loss, it can make your hallucinations more frequent.

There are some things about CBS hallucinations which make them different to the hallucinations caused by other conditions. Usually, with CBS you're aware - or can learn to recognise - that what you're seeing might be vivid but it is not real. CBS hallucinations only affect your sight, which means that people with CBS don't hear, smell or feel things that aren't there. People with CBS do not develop any obvious, complicated non-medical explanation about the cause of their hallucinations (sometimes called "delusions"). For example, someone with CBS wouldn't have thoughts that the people they were seeing wanted to hurt them.

If one day you find you're seeing a pattern, person, building or a landscape that you know is not really there, then don't be afraid to mention this to your GP or optician, who should be familiar with CBS. You may find it useful to take a copy of this information along with you.

What you see if you have CBS

The visual hallucinations caused by CBS can take many forms, ranging from simple shapes and dots of colours, simple patterns, straight lines or a network of branches, to detailed pictures of people, animals, insects, landscapes and buildings. When you have lost a large amount of your vision it may be difficult to see everyday things, but you may find that your CBS hallucinations are very detailed, and much clearer than your normal vision. The images can appear 'out of the blue', lasting for just a few minutes or in some cases, several hours.

At times, the hallucinations will fit alongside the background you are looking at, giving them an understandable feeling of being real, like seeing cows in a field when the field is actually empty or seeing a fence across the pavement. At other times, they will seem totally unreal, like seeing fantasy images such as dragons.

When you first develop CBS your visual hallucinations may happen quite often, you may see things every day and for long periods of time. Your CBS may stay like this for a number of months, but over time the hallucinations may become less frequent and they may eventually stop. However, some people's hallucinations carry on for longer and you may find that you are prone to hallucinations every now and again.