Fight for Sight fund two studies to investigate the cause of visual hallucinatory condition in people with sight loss

10 August 20

written by:

Róisín Treacy

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An older woman with her head in her hands, looking upset.

Fight for Sight is highlighting the need for more awareness and research into a visual hallucinatory condition, known as Charles Bonnet Syndrome (CBS), which is common in people with sight loss.

The charity is announcing funding for two research projects into the condition with the hope of finding a treatment or cure.

The condition

Charles Bonnet syndrome is a common side-effect of sight loss in which people experience visual hallucinations. The kinds of things people see with CBS is thought to fall into two main types:

1)     simple repeated patterns or shapes, such as grids or brickwork patterns

2)     complex hallucinations of people, objects and landscapes. These can vary from benign to quite alarming - for example, some people report seeing ‘snakes crawling out of people’s heads’ others see children in Victorian dress.

CBS hallucinations can be very detailed, and much clearer than the person’s everyday vision. The images appear very suddenly, lasting for just a few minutes or in some cases, several hours. The condition can cause huge distress to people who experience it, and can greatly impact on quality of life.

Charles Bonnet syndrome can happen to people with good mental health who have no history of psychiatric problems. Usually, people with CBS are aware – or can learn to recognise – that what they’re seeing isn’t real even though it’s very vivid.

Fight for Sight, together with partners Blind Veterans UK, Esme's Umbrella and Health and Care Research Wales, is funding two research projects at Cardiff University and University of Oxford to investigate the cause of the visual hallucinations associated with Charles Bonnet Syndrome, with the hope of eventually finding a cure. One study will investigate the possibility that peripheral (‘side’) vision is more ‘suggestible’ than central vision. While the second study will use a special type of MRI scan to measure the levels of chemicals in the visual areas of the brain to see whether they are abnormal in people with CBS.

Living with Charles Bonnet syndrome

Doctor Amit Patel lost his sight unexpectedly in 2013 and since then he regularly experiences visual hallucinations.

He said: “One day, not long after I lost my sight, I was walking down the stairs in my house and this girl suddenly appeared in front of me. I realised it was the girl from the horror movie ‘The Ring’. The hallucination only lasted about four seconds, but it was enough for me to fall down the stairs.”

Read Amit's story here

There is currently not enough data to show how many people in the UK have Charles Bonnet Syndrome, but it is estimated to be hundreds of thousands. In spite of this, scientists still do not understand why these hallucinations occur. There is also little awareness about the condition, and those who experience it often report that they were never made aware that this was something common in people with sight loss.


Fight for Sight is urgently calling for more funding to be invested in vital research for Charles Bonnet Syndrome, which is often misunderstood and can sometimes be mistakenly confused with the onset of dementia.

A team of researchers at Cardiff University, co-funded by Fight for Sight and Health and Care Research Wales, has developed a novel method to induce controlled hallucinations in the lab, which will allow them to explore the mechanisms underlying Charles Bonnet Syndrome. This project will use fully-sighted people to investigate the possibility that peripheral (‘side’) vision is more ‘suggestible’ than central vision.

Dr Matt J Dunn from the School of Optometry and Vision Sciences at Cardiff University is leading the study. He said: “In this study we are testing a hypothesis that following long-term central vision loss, patients with Charles Bonnet Syndrome pay more attention to their peripheral vision, which is more reliant on expectation and previous experience than central vision, and therefore prone to hallucinatory experiences. We will use a novel lab-based test to measure a person’s reliance on prior expectation when generating visual percepts. This test will be applied to fully-sighted people using visual stimuli shown to both central and peripheral visual locations. Our aim is to determine whether peripheral vision is more suggestible than central vision.”

While at University of Oxford, researchers funded by Fight for Sight, Blind Veterans UK and Esme’s Umbrella will use MRI scans to compare the brains of people with and without Charles Bonnet syndrome to look at how they differ.

Professor Holly Bridge is leading the study at University of Oxford. She said: “In the healthy visual system the eye provides input to a large area of the brain that allow us to see the world. There are specialised brain regions responsible for the processing of faces, objects, motion and colour. When the eye is no longer working these parts of the brain lose their input and we think this can lead to abnormal activity. In particular we will use a special type of MRI scan in this study to measure the levels of chemicals in the visual areas of the brain to see whether they are abnormal in CBS, leading to the hallucinations.”

It is hoped these two research studies will provide insight into the cause of Charles Bonnet syndrome hallucinations, which will help inform larger studies in the future and eventually to test whether there are interventions to help improve the condition.

Chief Executive of Fight for Sight, Sherine Krause said: “So much more needs to be done to understand Charles Bonnet syndrome. This is an area of research that little is known about and has largely been neglected, so we are very pleased to fund these two important research studies. With a better understanding of the causes of Charles Bonnet syndrome, we will be one step closer to developing a treatment and cure for the condition. However, more investment in eye research is needed to ensure we can continue transforming the lives of people with sight loss.”

Head of Programmes at Health and Care Research Wales, Michael Bowdery, said: “We are delighted to be working with Fight For Sight to support research into a condition that affects so many people but for which there is currently no known treatment or cure. We wish Matt and the team at Cardiff University the very best of luck.”

Donate to help fund research into Charles Bonnet Syndrome Read more about Charles Bonnet Syndrome Read more about Esme’s Umbrella