The Charles Bonnet Syndrome

People with Charles Bonnet Syndrome (CBS) experience visual hallucinations, which is particularly bizarre because of the fact that almost without exception CBS sufferers are blind or only partially sighted.   Hallucinations vary from person to person and one CBS patient may experience many different types of hallucination.  They may be simple – flashing lights or patterns.  On the other hand they can be incredibly complex – cartoon characters, famous people and even landscapes full of 17th century French soldiers have been reported!  Faces are very common, consistently described by sufferers as being ghoulish, with large ill-governed mouths and oversized teeth.  Think Ronaldinho, or Janet Street-Porter…

People with CBS aren’t mentally unstable.  At least no more so than the average person reading this article.  Neither are they asleep.  They are also usually completely aware that what they are seeing is a hallucination, and around three quarters either experience no emotional reaction to the visions, or actively enjoy what they see, many finding them a colourful and welcome addition to a world in which they can receive very little else in the way of visual input.

But arguably the most incredible fact about this bizarre condition is that it seems to be far more common than anyone in the medical world could ever have imagined – recent studies suggest that anything up to 40% of people with low vision also suffer from CBS, which is the equivalent of upwards of 75 million people around the world.

I wanted to write an article on CBS for two reasons.  Firstly because it must be one of the least recognised “common” conditions.  It is astounding to think that as many as 40% of people with low vision may be suffering from it.  But if you think about it, perhaps it makes sense – one recent study found that 77% of people with low vision that entered their trial had never heard of CBS, and how many of these people are going to willingly divulge to anyone about their hallucinations?  Probably even less than you’d think when you consider that the vast majority of these people are well into the autumn of their lives already and know that they risk being carted off into a home at the first signs of dementia!

Which brings me nicely on to my second reason; CBS is a condition which is only going to get more prevalent as our society continues to age, and more and more of us live long enough to suffer from diseases like cataracts, glaucoma and macular degeneration.  And one of the other big problems that this aging society brings is of course dementia, and I fear what happens once the CBS/Dementia co-morbidity rates start to rise.  Already we are seeing that up to a quarter of patients experience negative reactions to their hallucinations, and these are people with relative control of their mental faculties; imagine the distress these kinds of hallucinations could cause to someone who isn’t…

Nobody really understands the reasons behind CBS.  The theory that has the most amount of weight behind it is the “deafferentation theory”- which is similar to that seen with phantom limb syndrome.  In a person with normal vision, external visual stimuli is perceived by the retina and transmitted to the Primary Visual Cortex, from where it goes on to the Secondary Visual Cortex and then to the Visual Association Cortices which make sense of everything.  In this model, external stimulation has a controlling, inhibitory effect on endogenous activation of the cortex.  However when the visual pathways are damaged and this stimulation is removed then we begin to witness something called “cortical release phenomenon”, with waves of discharges being released from different areas in the brain.

And they can be released from a whole host of different areas.  One study has done more than any other to unlock the secrets of CBSand finding a charles bonnet syndrome treatment, using MRI to look at the brains of sufferers as they experienced their hallucinations.  Doing so they managed to map certain types of hallucination to certain types of brain activity (Santhouse AM, Howard RJ, Ffytche DH. Visual hallucinatory syndromes and the anatomy of the visual brain. Brain, Vol. 123, No. 10, 2055-2064).  They found that figures and landscapes are created by the Ventral Temporal Lobe, and faces in the Superior Temporal Sulcus, while the Dorsal Parietal Lobe seemed to be the source of visions which tend to persist, and which therefore may be more troubling to the sufferer.

CBS largely goes untreated, mostly because of a lack of awareness about the condition, but also because those in the medical world who know about it see it as a curiosity, and perhaps even a perk, that comes with low vision.  There have been a number of papers written about cases where it was deemed necessary to attempt treatment; cases where patients suffered from truly disturbing hallucinations, or ones that left them unable to live a normal life.  The approach to treatment very much appears to be a kind of “suck it and see” approach, by which I mean nobody really has a clue what to treat CBS with so they try anything under the sun – pretty much any type of psycho active drug that you could name has been used in at least one published study claiming success, but little more than that, and to this day there is very little known about why any particular treatment was successful.

Modi Mann is a copy writer who specialises on healthcare related topics and has been working for an organisation offering elective placements in developing countries specialising in medical elective projects.