Charles Bonnet syndrome (CBS) is a condition where people with significant vision loss experience vivid visual hallucinations, despite having no psychiatric illness or cognitive decline. It affects roughly one in six people with conditions like macular degeneration, glaucoma, or diabetic retinopathy. The hallucinations are a neurological response to vision loss, not a sign of mental illness.
Why Vision Loss Triggers Hallucinations
Your brain’s visual processing areas need a constant stream of input from your eyes. When eye disease reduces or cuts off that input, the visual parts of the brain don’t simply go quiet. Instead, they become hyperactive. Without real images to process, neurons in these regions begin firing spontaneously, generating images that feel real but have no external source.
Think of it like a radio picking up static when it loses a signal. Brain imaging studies show increased metabolic activity in the visual processing areas during hallucination episodes. Specific regions light up depending on the type of hallucination: areas that normally process faces become active when someone sees phantom faces, while pattern-processing regions activate when someone sees geometric shapes. Critically, the brain’s higher-level reasoning centers are not involved, which is why people with CBS typically recognize that what they’re seeing isn’t real. They don’t develop delusions or false beliefs about the hallucinations.
What the Hallucinations Look Like
CBS hallucinations are exclusively visual. There are no accompanying voices, sounds, or physical sensations. They range from simple to extraordinarily complex. On the simpler end, people may see geometric patterns, grids, flashes of color, or repeated shapes. More complex hallucinations can include detailed faces, small figures (sometimes called Lilliputian hallucinations), animals, buildings, or entire landscapes. Some people see strangers in period costumes. Others see flowers, trees, or intricate brickwork.
The images can appear suddenly and last anywhere from seconds to hours. They may be in vivid color or monochrome, and they can stay still or move. Many people describe the hallucinations as surprisingly sharp and detailed, sometimes clearer than their actual remaining vision. Episodes tend to happen more often in low light, during quiet moments, or when someone is alone and understimulated. The hallucinations are painless and carry no physical sensation, but they can be startling, especially the first few times.
Who Gets CBS
The common thread is significant vision loss. The eye conditions most frequently linked to CBS are age-related macular degeneration, glaucoma, cataracts, and diabetic retinopathy. Because these conditions become more common with age, CBS predominantly affects older adults, though it can occur at any age if vision loss is severe enough.
A 2025 systematic review found that CBS prevalence among ophthalmic patients ranges from about 12% to 18%, depending on the specific condition. That’s a substantial number of people, yet the syndrome remains widely underdiagnosed. The degree of vision loss matters: the more severe the visual impairment, the higher the likelihood of developing hallucinations. Social isolation and reduced sensory stimulation also appear to increase risk, likely because the brain has even fewer competing inputs to override the spontaneous visual activity.
The Fear of “Going Crazy”
One of the most damaging aspects of CBS is that many people who experience it never tell anyone. A survey of people living with the syndrome found that 60% feared being labelled as insane if they admitted to seeing things. Only 30% had ever revealed their hallucinations to another person. Another 30% lived in active fear that they were losing their minds.
This silence creates a cycle of unnecessary suffering. People endure distressing hallucinations alone because they assume visual hallucinations mean psychosis or dementia. In reality, CBS hallucinations arise from the eyes and visual brain, not from any psychiatric process. The defining feature of CBS is intact insight: you know the hallucinations aren’t real, even as you see them. That awareness is what separates CBS from psychotic disorders, where people typically believe their hallucinations are genuine.
How CBS Differs From Psychiatric Hallucinations
The distinction between CBS and psychiatric or neurological conditions that also cause hallucinations is important and usually clear. In schizophrenia or psychosis, hallucinations are most commonly auditory (hearing voices) and often come with delusions, disordered thinking, or paranoia. People experiencing psychotic hallucinations frequently believe the hallucinations are real. In CBS, hallucinations are purely visual, and the person recognizes they are not real.
In dementia with Lewy bodies, visual hallucinations also occur, but they’re accompanied by progressive cognitive decline, fluctuating alertness, and often movement symptoms similar to Parkinson’s disease. CBS requires that cognitive function remain intact. Some researchers have raised the question of whether CBS could occasionally be an early marker of dementia, so cognitive screening is part of a thorough evaluation. Other conditions that must be ruled out include epilepsy-related visual phenomena, medication side effects, and delirium.
How It’s Diagnosed
There is no blood test or brain scan that confirms CBS. Diagnosis is based on three core criteria: the person has significant vision loss, they experience recurring visual hallucinations, and they retain full awareness that the hallucinations are not real. Cognitive function must be normal, and there should be no psychiatric illness or other medical condition that better explains the symptoms. Doctors will typically check for medication side effects, perform a cognitive assessment, and sometimes order brain imaging to rule out other causes. Once those are excluded, the pattern of vision loss plus visual-only hallucinations with preserved insight points clearly to CBS.
Treatment and Coping
There is no standard medical treatment for CBS. For many people, simply learning that the condition exists and that it’s a recognized, benign neurological phenomenon provides enormous relief. That reassurance alone can reduce the distress significantly.
On a practical level, several techniques can help interrupt or reduce hallucinations. Increasing ambient lighting, especially in the evening, reduces episodes for some people. Staying socially active and mentally engaged gives the brain more competing input, which can suppress the spontaneous visual firing. Some people find that rapid eye movements, blinking deliberately, or shifting their gaze when a hallucination begins can cause it to fade. Turning on the television or radio, or simply moving to a different room, can also help by changing the sensory environment.
When hallucinations are severe, persistent, or cause significant anxiety, medications are sometimes tried. Antipsychotics, antidepressants, and anticonvulsants have all been used with mixed results. Case reports suggest that certain low-dose antipsychotics can reduce hallucinations in some individuals, but there are no large clinical trials establishing a reliable drug treatment. Medication is generally reserved for cases where the hallucinations are genuinely distressing and non-drug approaches haven’t helped.
Addressing the underlying vision loss, when possible, can also reduce symptoms. Cataract surgery, for instance, may restore enough visual input to quiet the overactive brain regions. Optimizing whatever remaining vision exists through better glasses, magnifiers, or improved lighting can help for similar reasons.
Long-Term Outlook
For many people, CBS hallucinations decrease in frequency and intensity over time. The brain appears to gradually adapt to the reduced visual input, and the spontaneous firing settles. In some cases, hallucinations resolve entirely within 12 to 18 months. For others, they persist for years but become less vivid or less frequent, and most people find them less distressing once they understand what’s causing them. If vision loss worsens, hallucinations may temporarily increase before the brain recalibrates again. The condition does not progress to psychosis, does not indicate cognitive decline on its own, and does not shorten life expectancy.