What is the cause of CBS?

The short answer is that nobody really knows. 

There is believed to be a strong correlation between diminished vision and CBS. That is, the vast majority of people living with CBS have some form of vision loss. It is believed that CBS is principally about how the brain responds to this deterioration of vision.

It has been hypothesised that vision loss significantly reduces visual input to the brain and this seems to lead to hyper-excitability in the upper reaches of the visual system. This neuronal hyper-excitability generates internal visual imagery that the person experiences as external (ie. part of their visual environment).

Some have likened CBS to phantom limb syndrome whereby a person still 'experiences' their amputated limb well after it has been lost. It is argued that the nerve pathways to the brain from the amputated region remain healthy and intact. Neuronal (brain) cells devoted to that specific amputated area can fire spontaneously which the person experiences as felt sensations (from the lost limb). 

However, the sensory deprivation type theory does not explain why only some people living with eye disease will experience CBS whilst others do not. Further, there are cases of people with CBS who have no vision loss. It is suspected that the missing link lies somewhere in the brain but exactly where and how this occurs remains unknown.


Is there a test for CBS?

Currently, there is no form of test (eg. blood, urine, biopsy, optical, fMRI scan) that can provide a positive reading for CBS. Presently, a CBS diagnosis is typically arrived at from excluding other possibilities such as neurological deficits (including dementia, Parkinson’s disease), side effects of (prescribed) medication or some form of psychiatric illness. 

Whilst there is no universally agreed upon diagnostic criteria for CBS, its core features seem to be:

  • Vision impairment (in eye or some part of the visual system)
  • Existence of repeated phantom images or visions
  • Full or partial insight into the unreality of what one sees (ie. no delusions)
  • No discernible cognitive or memory deficits
  • The visual images do not extend to other sense modalities (ie. no sounds, tactile or olfactory sensations associated with the imagery).


How long does CBS tend to last?

There are 2 aspects to this question:

(a) Episode duration

How long each episode lasts can vary enormously. CBS-affected individuals report that phantom images can last anywhere from a few seconds, minutes through to hours. 

How frequently the episodes occur also has a large range. For some, it may be a rare and fleeting monthly experience whilst for others the imagery can persist on a daily basis for extended periods of time. 

(b) Syndrome duration

The long-held view has been that approximately 60% of CBS cases will resolve within 12 to 18 months. However in a recent study (Cox & ffytche, 2014) of nearly 500 CBS-affected people, 75% reported that their symptoms continued for over five years.

Personal stories shared to the Foundation also indicate that for several people their CBS can last many years, even beyond a decade. This suggests that perhaps the true life-span of the syndrome has been under-estimated.


My mother was recently diagnosed with CBS. What can I do?

Being supportive, non-judgmental and empathic cannot be understated. Providing reassurance to your mother that she is not 'going bonkers' can be incredibly comforting. Reinforcing that she is not losing her mind and that the symptoms are a peculiar by-product of vision loss can reduce anxiety and fear.

Explore ways to help your mother (i) better adjust to her vision loss and (ii) maximise her remaining vision. Contact your mother's local low-vision rehabilitation service provider to explore a range of options that may be beneficial to her. This includes:

  • relevant visual aids (eg. anti-glare, night-light, magnifiers)
  • mobility assistance 
  • optimal home lighting
  • tips & useful gadgets for everyday tasks 
  • support groups
  • social options

Any of these initiatives can assist your mother feel more empowered to manage daily living tasks. Anecdotal evidence suggests that those who feel more in control of their situation tend to have less frequent CBS experiences. 

Don't assume that your mother necessarily wants to be rid of the images. Once she has understood that the condition is not linked to mental illness or dementia, she may well come to appreciate or value the phantom images. For about 15% of CBS cases, the person finds the images pleasant and a welcome addition to their lives. This is because CBS images tend to be far more vivid and detailed than their typical everyday perceptions, which have been dulled by vision loss.

If your mother finds the images annoying, disturbing or unwanted, then encourage her to try various strategies to counter their presence (see CBS Treatments). She is also welcome to call the CBS Foundation if she would like to talk to someone further about her experiences. A range of services are available which may be of interest to your mother (see CBSF Services).

If all else fails, as a last resort, consider seeing an ophthalmologist, neurologist or geriatrician who can explore a pharmacological treatment. Bear in mind though that current medications remain 'hit and miss' as no specific drug has been shown to effectively treat CBS symptoms in most, let alone all, cases.


The medical and nursing care staff have not heard of CBS. What can I do?

This unfortunate and frustrating scenario is an all-too-familiar reality across a range of medical and health care settings. One of the best things one can do is to access a position statement on CBS from a formal medical body such as the Royal College of Ophthalmologists and supply this document to the relevant doctor and/or allied health team. You can play an important role in educating medical and health professionals of this largely invisible syndrome. 

Click here to download such a position statement.


What type of eye conditions can lead to CBS?

Macular degeneration remains one of the leading risks for CBS (especially in western countries). However, all other forms of vision impairment including glaucoma, cataracts, diabetic retinopathy, retinitis pigmentosa (RP), and even enucleation (eye removal) can lead to CBS symptoms. In fact, damage to any part of the visual system – not just the eye itself- can result in Charles Bonnet syndrome. This includes damage to visual regions of the brain from a stroke or brain tumour.

What remains unknown to this day is why some people with macular degeneration (or any other form of vision impairment) will experience CBS whilst others do not.


Is there a cure for CBS?

Presently, there is no universally effective cure for CBS.

  • Sometimes, improvement in one's vision can bring an end to CBS.
  • Sometimes, utilisation of visual aids and optimal lighting can reduce symptoms.
  • Sometimes, behavioural interventions can be effective.
  • Sometimes, increased socialisation can be beneficial.
  • Sometimes, certain prescribed medications can lead to an end of CBS symptoms.
  • However, none of the above interventions have been found to work in the majority of cases.


What tend to be the emotional reactions to the CBS images?

Initially, the experience tends to be a mixture of anxiety and confusion as the affected individual does not know what is suddenly happening to them. In a recent survey of 492 CBS-affected people (Cox & ffytche, 2014), 38% had a 'fear-inducing' response at CBS onset whilst curiosity was also common (36%).

Many people living with CBS report that they were never questioned about, or given any forewarning of, the possibility of Charles Bonnet syndrome by eye health care practitioners. Left to make sense of their 'visions' on their own, worst case scenarios often roam in the person's thoughts. This can lead to persistent fear, distress and even depression. Much of this distress could be alleviated if the person received education about CBS during - or shortly after- their initial eye consultation.

Once the person comes to understand the nature of the syndrome, roughly two thirds (65-70%) come to feel a great sense of relief that they have no mental illness or impending dementia. Knowing they have a recognised medical condition - that is not associated with psychiatric or memory decline - can allay fears and be incredibly reassuring. Once familiar with the condition, a more neutral emotional response to the CBS imagery is often adopted.

Approximately 10-15% will continue to find their imagery pleasurable (or of novelty value) as often the imagery is more vivid and detailed than their everyday vision-impoverished world. 

Even when one understands the condition, roughly 30% will continue to find the imagery unpleasant, unwanted or stressful. For this latter group, their discomfort can be due to:

(a) the content and/or frequency of the images experienced,

(b) irritation that the imagery is ongoing with no signs of respite or

(c) (ongoing) concerns as to the actual cause of them. 


How many people have CBS?

No one knows the true prevalence rate of CBS.

Comprehensive studies of large samples of vision-impaired people have not yet been undertaken. Typically, studies mention that the condition is under-reported and under-recognised so that current estimates are probably conservative. 

Many clinical studies over the past 25 years have suggested that somewhere between 12% - 20% of all vision-impaired people will experience CBS. However, in more recent times, a new CBS picture is emerging. Gilmour et al (2009) found a prevalence rate of 34% and a 39% figure was reported by Cox & ffytche (2014). Also, O'Hare et al (2015) published a prevalence rate of 37.5%.

The great variation in reported prevalence rates is due to numerous factors including:

  • differences in the population studied.
  • the degree to which patients are willing (or reluctant) to disclose their symptoms to health professionals.
  • variability in definitions of what is deemed to be CBS.