Causes of Charles Bonnet Syndrome

The main cause of CBS is loss of vision and how your brain reacts to this loss.

Exactly how sight loss 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 by talking with you and in some cases doing tests, your doctor will be able to 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’s natural 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 that you have Alzheimer’s disease. However, it’s important to remember and reassuring to know that CBS is caused by sight loss only and not by any other health problem.

If the hallucinations cause you to feel anxious, you may also feel like you want 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 is more information on “talking about CBS” later in this booklet.

There are some 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’s 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.**

Certain things about CBS hallucinations 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 isn’t real, although it may appear vivid. CBS hallucinations only affect your sight, which means that you 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 that 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.

Charles Bonnet syndrome affects people who've lost most or all of their eyesight.

Who's affected and why?

Charles Bonnet syndrome affects people who've lost most or all of their eyesight.

It's more likely to occur if the loss of vision affects both eyes.

According to the Macular Society, up to half of all people with macular degeneration – a gradual loss of central vision – may experience Charles Bonnet hallucinations at some time.

It's thought there are more than 100,000 cases in the UK.

People of any age can be affected by Charles Bonnet hallucinations, but they tend to occur later in life after a person starts to lose their sight. The hallucinations often begin when a person's sight suddenly deteriorates.  People who may have lost a lot of their vision from an eye condition such as cataract, glaucoma or diabetic eye disease

The main cause of Charles Bonnet syndrome is thought to be vision loss and how the brain reacts to it. It's not clear how loss of vision leads to hallucinations, but research is beginning to help us better understand the relationship between the eyes and the brain. 

When a person starts to lose their sight, their brain doesn't receive as much information as it used to. It's thought the brain sometimes responds by filling in the gaps with fantasy patterns or images that it's stored. These stored images are experienced as hallucinations.

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.

It’s thought that there are more than 100,000 cases of CBS in the UK. Some research suggests that up to 60 per cent of people who are experiencing serious sight loss may develop it.