Over 250 years have passed since Charles Bonnet’s seminal essay, in which he described the symptoms of the syndrome that now takes his name [1]. Charles Bonnet Syndrome (CBS) describes the occurrence of visual hallucinations in people with significant visual loss and no underlying psychiatric illness [2].
Patients describe hallucinations ranging from unformed images, such as flashes and spots, to complex formed images like “acrobats balancing on bicycles” and “spiders crossing meals” [1]. Despite vivid hallucinations, patients uniquely retain insight that they are not real and often describe the nature of hallucinations as benign [3].
Yet the experience is not always harmless. Several studies investigating patients’ experiences of CBS highlight that a significant proportion of individuals suffer clinically relevant consequences, such as fear-inducing, longer-lasting hallucination episodes or concerns about impending insanity [4]. Since Bonnet’s original work, our understanding of CBS has advanced but remains limited, and clinical awareness is insufficient. This article explores current challenges in diagnosing CBS and highlights why improving awareness is essential for better research, management and patient care.
A prevalent but underdiagnosed condition
Recent evidence suggests CBS is far more common than previously believed. A 2022 systematic review reported a prevalence of around 20% among people with low vision [5]. Despite this, CBS remains underdiagnosed.
Stigma surrounding visual hallucinations and their perceived association with psychiatric conditions is stated as a major barrier to patients disclosing these symptoms [4]. These concerns are also not unfounded, with CBS frequently misdiagnosed as a neuropsychiatric disorder [6]. In parallel, clinician awareness of CBS is low, with a recent cross-sectional survey of 499 family physicians in Canada revealing that 55% were unaware of the diagnosis and 85% never discussed the possibility of CBS with patients presenting with visual loss [7]. A study revealed that among those with CBS who sought medical advice, one-third of patients felt that the professional did not understand the condition [4]. Awareness of CBS is low even amongst patients with visual impairment, with reports that two-thirds of patients with CBS had never heard of it when their symptoms began [4].
With an increasing incidence of visual impairment, it is crucial that physicians screen for and are aware of CBS as a possible differential diagnosis for visual hallucinations [8]. This is important as studies suggest that the majority of patients with CBS are relieved when they receive information on CBS or reassurance that these visual hallucinations do not represent sinister pathology [4,9]. Screening questions for CBS should therefore be incorporated into assessments of high-risk groups. Medical professions can further support patients by providing reliable information or signposting organisations such as Esme’s Umbrella, the national charity supporting people living with CBS.
Beyond visual impairment, studies have reported that old age and social isolation may be risk factors for CBS [10]. Recent data suggest that visual hallucinations in CBS were exacerbated during the Covid-19 pandemic, which may partly be explained by social isolation and loneliness [11]. Increasing research and awareness will equip medical professionals with the knowledge of risk factors and pave the way to better management, which may include social prescribing and community support.
Diagnostic criteria
Accurate diagnosis is key to appropriate management. It was only in 2019 that CBS was introduced into the Classification of Diseases – 11 as a standalone diagnosis [12]. A recent systematic review of the diagnostic criteria for CBS demonstrated considerable diagnostic heterogeneity across studies. For instance, whilst core features (visual hallucinations, insight into their unreal nature, vision loss and exclusion of confounding neuropsychiatric disorders) were general consistent, there was variability in defining hallucination properties, severity of vision loss and inclusion or exclusion of cognitive impairment [9]. Heterogeneity in the diagnostic criteria likely has important implications for translational observational and interventional studies.
The clinical research landscape
Research on CBS remains limited and dominated by case reports and small observational studies which, although valuable in advancing clinical practice, can lead to over-generalisation if excessively relied upon [1]. Under-diagnosis and poor awareness restrict recruitment for larger trials, slowing progress in understanding the underlying mechanisms and developing effective therapies. A search of clinical study registries (ClinicalTrials.gov, the ISRCTN registry, the EU clinical trials register, and the NIHR Clinical Research Network portfolio managed by Ophthalmology) revealed only four registered studies when ‘Charles Bonnet Syndrome’ and ‘visual release hallucinations’ were searched for.
Currently, no targeted medical treatment exists beyond improving vision where possible and reassurance [9]. However, emerging work is promising. Case studies suggest that oxygen therapy and antipsychotics may show promise for the pharmacological treatment of CBS, but further research is necessary to assess wider clinical applications [1,2]. The results of a recent randomised controlled trial investigating transcranial direct current stimulation in the treatment of visual hallucinations in CBS are particularly exciting and demonstrate that compared to placebo, inhibitory stimulation of the visual cortex resulted in a significant reduction in the frequency of visual hallucinations with no adverse effects reported [13]. Further research is required to understand long-term efficacy. Clinical research paves the way for better patient-centred diagnostics, treatments, and services [8].
Conclusion
Sight loss can be devastating and isolating, and CBS adds an additional, often frightening layer to this experience. Despite affecting a significant proportion of people with visual impairment, CBS remains under and inconsistently diagnosed, poorly understood and historically under-researched. Improving awareness of CBS amongst clinicians, patients and the wider community aims to reduce stigma and enhance patient identification, care and advocacy. This, coupled with the development of consistent diagnostic criteria, will likely propel more translational clinical research, which will form the foundation for new evidence-based guidelines to aid clinicians in the diagnosis and management of CBS.
References
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[All links last accessed January 2026]
Declaration of competing interests: None declared.
