Understanding the mysteries surrounding Charles Bonnet syndrome

Why do some people with vision loss experience hallucinations, while others do not? That’s one of the areas being looked into as researchers aim to uncover some of the mysteries surrounding the condition Charles Bonnet syndrome (CBS).

Optometrist and researcher, professor Jasleen Jolly of the Vision and Eye Research Institute at Anglia Ruskin University, has been working on a number of studies to shine light on CBS – hallucinations which can occur as a result of sight loss.

Up to half of all people with macular disease are believed to experience hallucinations at some stage. Professor Jolly is involved in four Charles Bonnet-related projects. These include: brain image analysis at University of Oxford, electric signal studies at Anglia Ruskin University, and two further prevalence studies.

At the Wellcome Centre for Integrative Neuroimaging (WIN) at University of Oxford, professor Jolly has been assessing sight loss patients’ MRI scans to assess brain activity changes.

She said: “To have that clarity of vision in those hallucinations, clearly there is something happening in the brain and it’s not an eye problem, especially as it can happen regardless of the underlying eye issue.”

As a result, the team is now testing a theory which looks at both the information transported from the eyes to the brain – known as ‘feed forward information’ - as well as what is called ‘feedback information,’ which originates in the brain because of a person’s memories and experiences.

Professor Jolly said: “What we think is happening is there is an imbalance between the two, because you’re not getting the information coming in from the eye, but you’re still getting the feedback information and that imbalance is then leading to these hallucinations. This theory is what we’re trying to test in this study, but why that is happening more in some people and not in others we’re not really sure.”

In Cambridge, Jolly and her team have begun using an electroencephalogram (EEG) to study brain signals in patients before, during and after their hallucinations.

I’ve just raised some money and I’ve got a new person starting in September to analyse that data and we should be able to try and pick out whether what the brain wave changes are and whether or not we can get a clue as to whether there’s a change in the brain activity that might help explain what’s actually going on that might give us a clue again as to what’s causing the hallucinations and why they’re there.

Assessing these brainwave recordings will allow the researchers to see if there is a change in the brain activity, which could help explain what is causing the hallucinations and why.

She added: “The information from those studies together will help us to determine what’s actually causing the hallucinations and once we know that, that might help us develop strategies to help support people.”

The hope is this will also help educate people in the field of ophthalmology and beyond.

Professor Jolly added: “My hope is that once we have completed this work and we can actually have the evidence base to show this is not psychological, that something real is going on here in the brain, then we can encourage more clinicians to ask about this.

“It will be easier to educate clinicians. Historically, chronic pain and fibromyalgia wasn’t taken seriously until the cause was found, Parkinson’s and even epilepsy weren’t taken seriously until the cause in the brain was found.

“Until we find what is happening in the brain, unfortunately the medical community doesn’t take things seriously and that’s what’s sparked me to push this work forward and do these studies.”

Your Charles Bonnet syndrome questions answered by professor Jolly:

Are hallucinations worse at night time?

“We did find different people had them worse at different times of the day. Some people found them worse in the morning, others at night, some people found them worse in different lighting or when doing certain activities. It seems to be very much on the individual.”

How can I tell if they are real or not?

“Try and interact with it. If it disappears it’s probably Charles Bonnet. If it’s a mouse but there is no evidence of droppings, then it’s not real. If nobody else can see it, it’s not real. Also, if the hallucinations are not in keeping with how you see things then it’s not real.”

Are they always silent?

They are, however professor Jolly explained “just like you have Charles Bonnet for vision, there are equivalent syndromes for the other senses…it’s all about how the brain processes sensory information.” So, if you have a hearing condition then you may hear things that aren’t really there too.

Can you get these hallucinations in your sleep?

“When I studied 20 years ago we were told no, it’s only when you’re awake but it’s been changed on its head. It can be when you have your eyes closed, or when you’re semi-awake.”

How frequent are they?

The impact of CBS on a person is very much an individual experience, and that also includes how often they occur.

“Everybody is so different but having them intermittently is more common than experiencing them more frequently.” Professor Jolly added that data published following the Covid-19 lockdowns showed more frequent hallucinations during this time.

She said: “What was published during lockdown in 2020 was these increased, so isolation seems to increase them, so does trauma, bad news, anything negative is probably going to increase them. As you get used to them, as things settle, they become easier to deal with. I don’t know if they decrease or if you notice them less.”

If you are interested in taking part in research, such as Professor Jolly’s projects, you can register to join our research participant database.

Watch Professor Jolly’s My Macular and Me Webinar in full on our YouTube channel.