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.
Charles Bonnet syndrome tends to cause two types of hallucination:
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.
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.
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.
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.
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:
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.
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.
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.
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.