Simple visual hallucinations
Flashing lights: Appear as flashes or flickers.
Geometric patterns: Grids, stripes, mosaic-like patterns.
Color perception abnormalities: The entire visual field may appear green (green vision or chloropsia)8).
Charles Bonnet Syndrome
Key Points at a Glance
Section titled “Key Points at a Glance”1. What is Charles Bonnet Syndrome?
Section titled “1. What is Charles Bonnet Syndrome?”Charles Bonnet Syndrome (CBS) is a condition characterized by complex visual hallucinations in individuals who have experienced partial or complete loss of vision. Cognitive function is preserved, and the absence of psychiatric illness is fundamental to this condition. In ICD-11, it is defined as “visual release hallucinations” 3).
The three core elements of CBS are visual hallucinations, ocular pathology, and intact cognition. The diagnostic criteria (Ffytche 2005) include the following four conditions1):
- Persistent or recurrent complex visual hallucinations
- Insight into the hallucinations (recognition that the hallucinations are not real)
- No other types of hallucinations
- No primary or secondary delusions
This condition was first described in 1760 by Swiss scientist Charles Bonnet, who reported his grandfather’s visual hallucinations. In the 1930s, neurologist George de Morsier named it Charles Bonnet Syndrome4).
Epidemiology
Section titled “Epidemiology”Reported prevalence varies widely. Estimates among visually impaired individuals range from 0.4% to 39%5), with some reports of 11–15% up to 40%6). In the UK, an estimated over 100,000 people experience CBS7). In Canada, it is suggested that about 1 in 5 (approximately 20%) of patients with low vision or vision loss may experience CBS3).
The prevalence by causative disease ranges from 2.8% to 20.1% in glaucoma patients (proportional to the severity of visual impairment)1), and the highest incidence is reported in AMD (age-related macular degeneration)1).
The problem of underreporting
Section titled “The problem of underreporting”CBS is significantly underreported. 21% of patients do not report visual hallucinations to anyone, 64% report only to family members, and only 15% report to healthcare professionals (Vukicevic & Fitzmaurice)4). A 2009 study found that only 9% of CBS patients consulted a healthcare provider6). Physicians’ awareness of CBS is only 45%3), and a 2010 Sydney survey found that only 2 out of 343 general practitioners knew about CBS4).
The stigma of misunderstanding visual hallucinations as a “sign of mental illness” prevents patients from seeking medical attention and reporting.
Q
How common is Charles Bonnet syndrome?
A
The estimated prevalence among all visually impaired individuals varies widely from 0.4% to 39%, and precise figures have not been established5). In Canada, it is said to affect 1 in 5 people with low vision3). Due to fear of being mistaken for a mental illness, underreporting is common, and the actual prevalence may be higher than reported.
2. Main symptoms and clinical findings
Section titled “2. Main symptoms and clinical findings”Subjective symptoms
Section titled “Subjective symptoms”Visual hallucinations in CBS are classified into two types: “simple” and “complex.”
Complex visual hallucinations
People/faces: Faces of strangers1), deceased family members4), children7).
Animals: Dogs4), sheep, horses3), etc.
Scenes: flying cars, hockey practice scenes3), hallways3), etc.
Other characteristics of the visual hallucinations are described below.
- Preserved insight: All patients recognize that the hallucinations are not real.
- Duration: From seconds to hours. Ranges from fleeting (seconds to minutes) to persistent7).
- Frequency pattern: Three types: episodic, periodic, and continuous.
- Triggers: Fatigue, stress, changes in light levels, staring at a white wall, sensory deprivation5)6). More common with eyes open and increase during sensory deprivation6).
- Spontaneous resolution: May disappear with repeated blinking or rapid eye movements5).
- Auditory CBS (ACBS): A subtype where musical hallucinations occur in patients with sensorineural hearing loss. Worsens when hearing aids are not worn2).
In retinitis pigmentosa, complex visual hallucinations of faces of people or animals, as in CBS, are known to occur.
Clinical Findings
Section titled “Clinical Findings”There are no specific neurological or ophthalmological findings unique to CBS. Objective items that physicians should confirm are listed below.
- Visual acuity loss: Visual acuity less than 20/50 is associated with CBS, but it can also occur with acuity around 20/40 to 20/508).
- Visual field defects: Various patterns such as bilateral temporal quadrantanopia1), unilateral visual field loss4), and arcuate scotoma8). Hallucinations often occur in the area of visual field loss (though not always)8).
- Cognitive function tests: Exclude dementia using MMSE or MoCA. Cognitive function in CBS patients is preserved (e.g., MMSE 28 points1), MoCA 30 points5)).
- The majority of CBS hallucinations are located centrally and are colored (Khan et al.)8).
Q
Is there a way to make the hallucinations disappear on one's own when they occur?
A
It has been reported that repeated blinking or rapid eye movements can make the visual hallucinations disappear 5). Switching to bright lighting or increasing visual stimulation (such as watching television) is also considered effective. Closing the eyes is another option.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”The most recognized risk factors for CBS are worsening vision and advanced age. It often occurs with sudden vision loss and is not seen in individuals who are congenitally blind or have been blind for a long time.
The main causative diseases and conditions are listed below.
- AMD (age-related macular degeneration): The most frequent cause of CBS.
- Glaucoma: Prevalence 2.8% to 20.1% (proportional to severity of visual impairment) 1).
- Retinitis pigmentosa: Visual hallucinations (CBS) are recognized as a known complication.
- Cataract: There are reports of legal blindness due to severe bilateral nuclear sclerotic cataracts causing CBS 6).
- Diabetic retinopathy, optic neuritis, high myopia: All are listed as related eye diseases.
- Vascular lesions: CRAO, RVO, temporal arteritis, occipital lobe infarction. About 20% of strokes result in visual or perceptual impairment4).
- Traumatic brain injury (TBI/mTBI): Up to 69% of patients experience visual disturbances after mTBI, which can trigger visual hallucinations3). There are case reports of hallucinations developing 8 months after mTBI and persisting for over 5 years3).
- Pituitary adenoma: There are reports of CBS due to compression of the optic chiasm1).
- Multiple sclerosis: Cases have been reported following vision loss due to untreated MS6).
- After ophthalmic procedures: Can be triggered after cataract surgery, laser iridotomy, anti-VEGF injections, or enucleation.
Other risk factors include social isolation, cortical atrophy, and cognitive impairment. Psychosocial factors (social isolation, loneliness) are also associated with CBS6). There is no consensus on sex differences, but some studies suggest a higher prevalence in women.
Q
Can visual hallucinations occur even without mental illness?
A
CBS does not involve mental illness. It occurs while cognitive function is preserved, and patients are aware that the hallucinations are not real (preservation of insight). However, because it is necessary to differentiate it from mental illness, it is important to undergo evaluation by a doctor at the initial consultation.
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”Standardized diagnostic criteria for CBS have not been established. Diagnosis is clinical, based on the presence of visual impairment, characteristics of complex visual hallucinations, and exclusion of other diseases.
ICD-11 defines CBS as “visual release hallucinations” and requires the following 3):
- Complex visual hallucinations in people who have experienced partial or complete vision loss
- Hallucinations are exclusively visual and usually temporary
- Exclude schizophrenia and other primary psychotic disorders
Tests to be performed
Section titled “Tests to be performed”Ophthalmic examination
- Visual acuity test, visual field test (Humphrey 24-2)
- OCT (evaluation of RNFL thickness, etc.) 8)
- Slit-lamp examination
Neurological examination and imaging
- Head CT/MRI: to rule out stroke, tumor (including pituitary adenoma) 4)8)
- EEG: to rule out epileptic seizures8)
Cognitive function assessment
- MMSE, MoCA: screening for dementia5)1)
Blood and other tests
- CBC, RPR, CRP, FTA-ABS, ESR, vitamin B12, folate, methylmalonic acid, homocysteine8)
- Urine toxicology screen5)
- Medication review: check for drugs that may induce hallucinations (e.g., digoxin, PDE5 inhibitors)8)
- Ishihara color vision test (if chromatopsia is the main symptom)8)
Differential Diagnosis
Section titled “Differential Diagnosis”The key to diagnosis is to exclude causes of visual hallucinations other than CBS.
| Disease/Condition | Differentiating Points |
|---|---|
| Dementia with Lewy bodies | Accompanied by cognitive decline and parkinsonism. CBS may later progress to dementia in some cases. |
| Migraine with aura | Typical aura such as scintillating scotoma. Often accompanied by headache. |
| Epileptic seizure | Abnormal waves on EEG. Visual hallucinations are brief and stereotyped |
| Acute psychotic disorder | Lack of insight. Accompanied by other hallucinations or delusions |
| Substance use disorder | Check medication history and alcohol withdrawal history7) |
5. Standard Treatment
Section titled “5. Standard Treatment”No curative treatment for CBS has been established. The mainstay of management is empathy and reassurance, along with patient education 6). Patients often experience more stress from concerns about being perceived as having a mental illness than from the content of the visual hallucinations, making explanation of the condition the most important intervention.
The SHaPED trial showed that education and promotion of symptom reporting in at-risk patients lead to improved outcomes 6). Patients who received CBS education had better outcomes, while those lacking information had poorer prognoses 3).
Non-Pharmacological Therapy
Section titled “Non-Pharmacological Therapy”The following methods are safe and worth trying.
- Repeated blinking: May cause visual hallucinations to disappear 5)
- Rapid eye movements: Effective in interrupting visual hallucinations 5)
- Eye closure: May be effective as hallucinations are more common when eyes are open
- Bright lighting: Reduces sensory deprivation
- Reducing social isolation and promoting socialization: Loneliness is associated with CBS4)
- Stress reduction
- Increasing visual stimulation (e.g., television, reading)
- Vision rehabilitation (e.g., convergence training, especially recommended for CBS after mTBI)3)
- Optimizing hearing aids (for ACBS: auditory-type CBS, as symptoms worsen without hearing aids)2)
If the underlying eye disease is correctable, treatment may lead to spontaneous remission of visual hallucinations. Reports include resolution of hallucinations after photodynamic therapy (PDT) in AMD patients, and disappearance of CBS after cataract surgery. A case has also been reported where hallucinations resolved one month after resuming prescribed glasses5).
Pharmacotherapy (case report level)
Section titled “Pharmacotherapy (case report level)”There is no pharmacotherapy with strong evidence. The following are reports from case reports or small series, and no strong recommendation is made. Individual consideration should be given in collaboration with multiple specialties (ophthalmology, psychiatry, neurology)6).
The main reported medications are shown below.
| Drug class | Drug name and dose | Reported effect |
|---|---|---|
| Antipsychotics | Olanzapine 5 mg/day | Complete resolution of visual hallucinations within 2 weeks1) |
| Antipsychotics | Risperidone 1 mg → 2 mg at bedtime | Significant reduction in frequency and intensity (ACBS) 2) |
| Antipsychotics | Haloperidol 2 mg during the day + 4 mg in the evening | Most effective in cases with delirium 6) |
| Antipsychotics | Quetiapine | Effective in some reports 6) |
| Antiepileptic drugs | Carbamazepine + Clonazepam | Successful in 6 cases of ACBS (antipsychotics ineffective) 2) |
| Antiepileptic drugs | Topiramate 150 mg × 2 | Effective in a case with traumatic brain injury (combined with escitalopram) 7) |
| Antiepileptic drugs | Valproic acid 500 mg × 2 | Partial improvement (case with delirium) 6) |
| SSRI | Escitalopram 5 mg | Case with traumatic brain injury (combined with topiramate) 7) |
| Other | Mirtazapine, venlafaxine, donepezil | Limited reports available 6) |
Q
Do medications work for Charles Bonnet syndrome?
A
Standardized pharmacotherapy has not been established, and evidence remains at the case report level. Cases of improvement have been reported with antipsychotics such as olanzapine, risperidone, and haloperidol, as well as antiepileptic drugs such as carbamazepine and topiramate 6). When considering pharmacotherapy, decisions should be made on an individual basis in collaboration with psychiatry and neurology departments.
6. Pathophysiology and Detailed Mechanisms
Section titled “6. Pathophysiology and Detailed Mechanisms”The underlying mechanism of CBS is not fully understood. Currently, the following four theories have been proposed, and they partially overlap.
Main Pathophysiological Theories
Section titled “Main Pathophysiological Theories”1. Deafferentation theory (most widely accepted)
This theory proposes that loss of afferent neurons responsible for visual transmission leads to abnormal hyperexcitability in the visual cortex 6). It is thought to involve increased presynaptic release of neurotransmitters, increased postsynaptic receptor numbers, and decreased release of inhibitory neurotransmitters. Neurons in the lateral geniculate nucleus (LGN) undergo deafferentation after vision loss, leading to spontaneous neural excitation 8). Deafferentation due to sensory deprivation in the V1 and V2 areas triggers spontaneous neural activity 7).
2. Perceptual release theory
This theory proposes that perceptual pathways are normally suppressed by higher cortical centers, but when perception decreases, this suppression is released, resulting in visual hallucinations 6)4). A decrease in serotonin concentration in the visual cortex is suggested to be involved.
3. Sensory deprivation theory
Even in healthy individuals, visual deprivation can cause hyperexcitability of the visual cortex. Normally, sensory input suppresses this hyperexcitability, but in visually impaired individuals, reduced sensory input leads to visual hallucinations according to this theory1).
4. Release theory
This theory proposes that neural deficits in the visual pathway generate abnormal signals, and the mixture of these abnormal signals with normal visual activity causes visual hallucinations1).
Similarity to phantom limb
Section titled “Similarity to phantom limb”CBS is sometimes compared to a visual “phantom limb”4)8). Similar to phantom limb pain after amputation, it is understood as a cortical release phenomenon where the visual cortex attempts to “fill in” the area that has lost sensory input through autonomous activity8).
Involvement of neurotransmitters
Section titled “Involvement of neurotransmitters”Acetylcholine, dopamine, and serotonin are suspected to be involved6). These neurotransmitter systems are thought to be related to the mechanism by which antipsychotics and antiepileptic drugs alleviate symptoms.
Mechanism of auditory CBS
Section titled “Mechanism of auditory CBS”In auditory CBS (ACBS), maladaptive neuroplastic changes in the auditory cortex due to auditory deprivation are thought to generate spontaneous activity, leading to musical hallucinations 2). fMRI studies have reported activation of brain regions associated with music perception (auditory cortex) during visual hallucinations 2).
7. Latest Research and Future Perspectives (Research-Stage Reports)
Section titled “7. Latest Research and Future Perspectives (Research-Stage Reports)”Electromagnetic Stimulation Therapy
Section titled “Electromagnetic Stimulation Therapy”Preliminary studies on electromagnetic stimulation therapies such as transcranial magnetic stimulation (TMS) have been conducted, and temporary symptom relief has been reported 4). However, formal approval has not been obtained at this time.
SHaPED Trial Framework
Section titled “SHaPED Trial Framework”A framework has been reported in which educational interventions in the emergency department (education for at-risk patients and promotion of symptom reporting) improve outcomes 6). Developing a systematic screening program to prevent diagnostic delay of CBS is a future challenge.
High-density EEG studies of brain activity
Section titled “High-density EEG studies of brain activity”High-density EEG studies comparing brain activity during and without visual hallucinations in CBS patients have been conducted (Piarulli et al. 2021) 7). The neural circuits involved during hallucinations are being elucidated.
Clarifying the link with dementia
Section titled “Clarifying the link with dementia”It is known that some CBS patients later develop dementia or dementia with Lewy bodies. Whether CBS can be an early marker of dementia or is merely a confound due to age remains to be clarified. It has also been suggested that CBS patients may have higher mortality compared to the general population (mortality marker hypothesis), and long-term natural history studies are needed.
Research on auditory CBS
Section titled “Research on auditory CBS”ACBS (auditory CBS) has only been reported in about 38 cases in the English literature 2), making it an extremely rare disease concept. Elucidation of neural circuits targeting the auditory cortex and development of targeted therapies are listed as future research tasks 2).
8. References
Section titled “8. References”- Ghabi H, Maamri A, Hajri A, Zalila H. Charles Bonnet Syndrome Related to a Pituitary Adenoma: A Case Study in a Tunisian Woman. Case Reports in Psychiatry. 2023;2023:9979128.
- D N, D L, B L, et al. Echoes of the Mind: Auditory Charles Bonnet Syndrome. Cureus. 2024;16(8):e66120.
- Campbell C, Manocha RH, Hill V, Debert CT. Charles Bonnet Syndrome Following a Mild Traumatic Brain Injury. Cureus. 2024;16(10):e70638.
- Voit M, Jerusik B, Chu J. Charles Bonnet Syndrome as Another Cause of Visual Hallucinations. Cureus. 2021;13(1):e12922.
- Somoza-Cano FJ, Abuyakoub A, Hammad F, Jaber J, Al Armashi AR. Nonpsychotic Hallucinations and Impaired Vision: The Charles Bonnet Syndrome. Cureus. 2021;13(8):e16801.
- Karson C, Kang C, Albrecht B, Levin G. Charles Bonnet Syndrome With Superimposed Delirium. Cureus. 2022;14(8):e27570.
- Irizarry R, Sosa Gomez A, Tamayo Acosta J, Gonzalez Diaz L. Charles Bonnet Syndrome in the Setting of a Traumatic Brain Injury. Cureus. 2022;14(9):e29293.
- Bhatnagar A, Ishihara R, Pakravan M, Charoenkijkajorn C, Lee AG. Chloropsia in the Charles Bonnet syndrome. Am J Ophthalmol Case Rep. 2022;28:101703.