Many people who lose their sight start seeing things they know aren't real – a phenomenon known as 'Charles Bonnet syndrome'.
These hallucinations may be simple patterns or vivid, detailed images of people or buildings. They are only visual, and do not involve hearing things or any other sensations.
It's important to understand that they're caused by failing eyesight and not any mental health problem or dementia.
People with Charles Bonnet syndrome are normally aware that the visions aren't real, even if they are vivid.
If you're experiencing hallucinations, see your doctor for a diagnosis of the cause.
What kind of things do people see?
Charles Bonnet syndrome tends to cause two types of hallucination:
- Patterns and lines – like brickwork, netting, mosaic or tiles.
- Detailed pictures of people or places, and sometimes whole scenes such as landscapes or groups of people. These may be life-size or reduced or enlarged in size, and may be the same every time so they become familiar. The hallucinations may appear out of the blue and carry on for a few minutes or sometimes several hours. They can seem real – such as cows in a field – or unreal, such as pictures of dragons.
Generally, the hallucinations can be in black and white or in colour, and may involve movement or be static. The images themselves are not normally scary, but the experience can be frightening.
Who is affected, and why?
Charles Bonnet syndrome affects people who have lost most or all of their sight. It's more likely to happen if there is loss of vision in both eyes.
It can affect people at any age but usually develops after losing sight later in life. The hallucinations tend to develop after sight has suddenly worsened.
When people lose their sight and their brain is not receiving as many images as it is used to, it's thought that it responds by generating new fantasy pictures, which are experienced as though they were actually seen.
These experiences seem to happen when nothing much is going on – when the person is sitting alone, somewhere quiet that is familiar to them, or when they are lying in bed at night.
How common is it?
There are thought to be more than 100,000 people with Charles Bonnet syndrome in the UK. It happens to a significant proportion of people with loss of vision.
According to the Macular Society, up to half of all people with macular degeneration (a gradual loss of central vision) may experience Charles Bonnet syndrome.
How might the hallucinations affect the person?
Visual hallucinations are a normal response of the brain to visual loss, but Charles Bonnet syndrome is not widely known and many people worry about what it means and fear they may be developing a serious mental illness or dementia.
It can cause practical problems too. People who see complex hallucinations may find it difficult to get around. Streets and rooms may be distorted in shape, and brickwork or fencing may appear directly in front of the person, making it difficult to judge exactly where they are and whether they can walk straight ahead. Some people can overcome this problem by having good knowledge of their surroundings.
The more complicated hallucinations may be unsettling. Although the visions may not be of anything frightening, it can be disturbing to suddenly see strangers in your home or garden.
For most people, the hallucinations will improve with time – episodes become shorter and less frequent.
Recent evidence suggests most people will still have occasional hallucinations five years or more after they first started.
If the hallucinations do stop entirely, there is always a chance that they'll reappear after a further decline in vision.
How is Charles Bonnet syndrome diagnosed?
There isn't a test for Charles Bonnet syndrome, so doctors diagnose the condition by taking a detailed medical history and record of the person's symptoms and ruling out other possible causes of hallucinations.
Charles Bonnet syndrome may be diagnosed in a person who:
- has some loss of vision
- reports seeing complex, persistent or repetitive hallucinations
- is aware they're not real
- does not seem to have signs of dementia or mental illness
Can it be treated?
There is no cure for Charles Bonnet syndrome.
Simply understanding that the hallucinations are a normal consequence of visual loss can be hugely reassuring and help the person come to terms with the condition.
Techniques can be tried when the hallucinations come on, which may help.
For those with serious disturbing hallucinations, a number of medicines are available, although none are effective for everyone and the side effects must be weighed up against the benefits.
What techniques can help?
- Make a change to see if they disappear – for example, switch a light on if they happen in the dark
- Try moving your eyes from left to right once every second for up to 30s without moving your head
- Try staring at the image, blinking rapidly or reaching out to touch the vision – for some, this makes it fade
- Moving around or performing a task (such as getting up to make a cup of tea) may help
- Hallucinations may be worse when you're tired or stressed, so try to make sure you get enough sleep at night
Some people overcome their fear by getting to know the figures in their visions. One man with Charles Bonnet syndrome describes how, when he wakes up in the morning, he says to the figures he is seeing: "Right, what have you got in store for me today?" This allows him to have some control over the way he feels about his visions.
What support is available?
It may help to talk over feelings with a counsellor, psychologist or psychiatrist, who may be able to help you cope with the hallucinations. See your doctor for a referral.
There are few support groups and forums specifically for people affected by Charles Bonnet syndrome, but there are many support groups for people with visual impairment and the Macular Society has local support groups and an online community for those affected by macular degeneration and Charles Bonnet syndrome.