A woman in her late seventies, living alone in Co Mayo, starts seeing Victorian children in her sitting room. They are silent. They appear in the late afternoon, sit on the rug for twenty minutes, and vanish. She knows perfectly well they are not there. She also knows exactly what it would sound like if she said it out loud, so she tells nobody: not her daughter, not her GP, not the consultant treating her macular degeneration.
That story is a composite, but there is nothing unusual about it. Charles Bonnet syndrome is one of the most common consequences of sight loss and one of the least discussed. People who experience it very often say the same thing first: I thought I was losing my mind. They are not.
TL;DR
- Charles Bonnet syndrome (CBS) causes vivid, silent visual hallucinations in people whose sight is failing. It is a consequence of sight loss, not a mental illness and not dementia.
- It affects roughly one in five people with low vision, including 20.8% of people with geographic atrophy from age-related macular degeneration.
- Almost nobody mentions it. In the landmark Lancet study, only 16 of 60 people with CBS had ever raised it with a doctor, and just one of those 16 got the correct diagnosis.
- People with CBS keep full insight: they know the images are not real, and nothing is heard, smelled or felt.
- There is no cure, but reassurance helps enormously, and rapid blinking, side-to-side eye movements or changing the light level can interrupt an episode.
- Vision Ireland runs the country’s first CBS peer support group (InfoLine 1800 911 250) and Fighting Blindness offers free counselling on 01 674 6496.
What Charles Bonnet syndrome actually is
The Swiss philosopher Charles Bonnet described it in 1760, after his grandfather, whose sight had failed following cataract surgery, began seeing birds and patterned tapestries that were not there. The man was sharp, rational and entirely aware the images were illusions. The definition has barely changed since.
CBS produces spontaneous visual hallucinations in people with damaged sight. They are silent. They involve vision only. And crucially, the person retains insight: they know what they are seeing is not real, which is precisely what separates CBS from psychosis.
The images come in two broad types. Simple hallucinations are geometric: grids, lattices, brickwork patterns, flickers of colour drifting across the field of view. Complex hallucinations are formed and detailed: faces, animals, small figures, whole landscapes. Two men from the north of Ireland described their experiences to RTÉ in 2024. One looked down to find his daughter’s dinner plate crawling with insects. The other watched a tiger stroll down Royal Avenue in Belfast, to the delight of his children. Neither man thought the tiger was real. That is the point.
How common is it, and why has nobody heard of it?
Estimates range from under 1% to 30%, largely because studies define the condition differently and because patients are so rarely asked. The better recent figures cluster around 20% of people living with low vision, and a 2025 Danish study of people with geographic atrophy, the advanced dry form of age-related macular degeneration, found CBS in 20.8%.
Those numbers matter a great deal here, because AMD is the most common cause of sight loss in people over 50 in Ireland, and Fighting Blindness estimates that around 7% of Irish people over 50 are living with it. Apply even a conservative CBS rate to that population and you have many thousands of people seeing things they have never mentioned to anyone.
The silence is well documented. In Robert Teunisse’s 1996 Lancet study, 505 people with sight loss were screened and 60 met the criteria for CBS. All 60 had full insight into the unreal nature of what they saw. Only 16 had ever raised it with a doctor, and the correct diagnosis had been made in exactly one of those 16 cases. Every single participant was relieved to be told their hallucinations were not a sign of mental illness.
Clinicians carry some of this too: research suggests about a third of people with CBS believed their own doctor was unsure about the condition or had not heard of it.
Why the brain does this
The honest answer is that we are not certain. The long-standing explanation is the release or deafferentation theory: when the retina stops sending signals, the visual cortex does not fall quiet. It carries on firing, and in the absence of real input it generates its own imagery. The brain, in effect, fills the silence.
That story is intuitive and may still be broadly right, but a 2024 study measuring the main excitatory and inhibitory chemicals in the visual cortex of people with CBS found no difference from matched controls, so the mechanism remains open. What is not in doubt is the company CBS keeps: it sits alongside tinnitus and phantom limb sensation as something the brain does when a sensory channel goes quiet. Nobody thinks tinnitus means you are losing your mind.
It is not dementia. Here is how to tell.
This is the fear that keeps people silent, so it is worth being precise. In CBS, the hallucinations are visual and nothing else, they are silent, and insight is preserved. Thinking, memory and judgement are unaffected, and correctly diagnosed CBS does not mean you are more likely to develop dementia.
Visual hallucinations in dementia with Lewy bodies arrive alongside other changes: fluctuating alertness, memory and concentration difficulties, slowed movement, stiffness or tremor, vivid dreams acted out in sleep, and falls. Insight is often incomplete or lost.
So the things that warrant assessment rather than reassurance are: hallucinations involving hearing, smell or touch as well as sight; any loss of conviction that the images are unreal; new confusion or memory change; and new tremor, stiffness or unsteadiness. A sudden change in vision itself, or new flashes and floaters, is a separate matter and needs urgent attention. None of this is a reason to keep quiet. It is a reason to speak up, so the right answer can be found.
What actually helps
There is no cure, and the medical options are thin. Antipsychotics, anticonvulsants, anti-dementia drugs and SSRIs have all been tried, but the evidence sits almost entirely in individual case reports and no medication carries a definitive recommendation. Most people are prescribed nothing.
Reassurance and understanding. Simply being told what CBS is, that it is common, and that it says nothing about your mental health, measurably reduces its psychological impact. For many people that alone is the whole treatment.
Interrupting an episode. People living with CBS have developed their own techniques, sometimes called brain shunting: blink rapidly several times; move your eyes from side to side without turning your head; make the room brighter; stand up, walk into another room, or start a different task; put the radio on or ring someone. The common thread is competing stimulation and shifted attention. What works varies: some find that looking straight at a hallucination and mentally naming it makes it fade, while others do better ignoring it entirely.
Managing the triggers. Fatigue, stress, low arousal, poor lighting and long stretches alone all make episodes more likely. Research links loneliness and low mood to finding the hallucinations more distressing, which is a strong argument for company, routine and daylight rather than for tablets.
Making the most of the sight you have. An up-to-date prescription, proper task lighting, magnifiers and low-vision aids, and treating whatever is treatable in the underlying eye condition all reduce the sensory gap the brain is trying to fill.
Where to get support in Ireland
Vision Ireland, formerly the NCBI, has established the first peer support group in the country specifically for people living with Charles Bonnet syndrome. It meets online monthly, with plans to gather in person twice a year, and their Community Resource Workers will also talk through your experience one to one. Ring the InfoLine on 1800 911 250 to ask about the group and about local services.
Fighting Blindness runs Insight Counselling, a free and confidential service for anyone affected by sight loss, including family members: 01 674 6496 or [email protected].
Your GP and eye clinic. You are entitled to raise this, and clinicians are now being actively encouraged to ask about it. If the word hallucination feels too loaded, borrow the phrasing researchers recommend to doctors and turn it around: “Some people with eye problems like mine see things that aren’t really there. That has been happening to me.” A note of what you see, when it happens and how long it lasts makes the conversation far easier.
Esme’s Umbrella, the UK charity behind much of the global awareness effort, is a useful further resource, and CBS Awareness Day falls on 16 November each year. In Northern Ireland, RNIB NI runs its own peer support group.
The thing worth remembering
Charles Bonnet syndrome is the brain doing something extraordinary with too little information. It is not a warning about your mind, it is a consequence of what has happened to your eyes. In the Teunisse study, only 28% found their hallucinations genuinely distressing, and in 77% of cases the images carried no personal meaning at all. The bigger harm, for most people, is the silence around it.
If you or someone close to you has been seeing things and saying nothing, that is the part worth changing this week. Tell one person. Ring the InfoLine.
At Críonna Health we write about ageing as it actually happens, including the parts people find hard to raise. This article is for general information and is not a substitute for individual medical advice: if it described something familiar, bring it to your GP or optometrist.
📷 Photo by Ahmet Yüksek on Unsplash
