A video from The Macular Society explaining Charles Bonnet hallucinations
After Nina Chesworth from Manchester completed a fundraising walk to raise awareness of a little-known physical condition which sometimes causes disturbing hallucinations, we bring you our guide to the strange world of Charles Bonnet syndrome.
What is Charles Bonnet syndrome (CBS) and who does it affect?
The NHS describes Charles Bonnet syndrome as a condition which causes a person whose vision has started to deteriorate to see things that aren't real.
The hallucinations are only visual and don't involve hearing things or any other sensations.
Named after an 18th century Swiss scientist and philosopher who first described the condition, the syndrome's symptoms are not a sign of mental illness or dementia.
CBS is common among people who have sight loss but low awareness of the condition means those affected often do not get the support they need.
The Macular Society says 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 in people of all ages.
What is a visual hallucination and what does it look like?
People experience visual hallucinations in the same way as really seeing something.
They may be simple patterns or detailed images of events, people or places and may be slightly frightening when first experienced.
People with Charles Bonnet syndrome are usually aware that the visions are not real, even if they are vivid.
They often appear without warning and can last from a few seconds to as long as a day or more.
What causes CBS?
The main cause of Charles Bonnet syndrome is thought to be the brain's reaction to vision loss.
A person's brain doesn't receive as much information as it used to when their sight begins to deteriorate.
It is thought the brain can respond by filling in the gaps with fantasy patterns or images, stored images experienced as hallucinations.
Medics still do not understand how loss of vision can lead to hallucinations, although researchers are trying to understand the relationship between the eyes and the brain.
What should I do if I see hallucinations?
Always see your GP if you're experiencing hallucinations so they can investigate the cause.
There is currently no medical cure for CBS and charities say more research is needed to understand the condition.
These include altering your surroundings and carrying out eye exercises.
The Macular Society offers a telephone support group for people with CBS.
Contact the charity's Advice and Information Service on 0300 3030 111 to complete the referral form or Make a referral for advice and information.
The Society says Charles Bonnet syndrome can last from days to many years but for most people the hallucinations will improve over time to occur only occasionally.