Screening for Charles Bonnet syndrome: Should the definition be reconsidered?

Purpose: Charles Bonnet syndrome (CBS) is a condition in which individuals with visual impairment (VI) and with no cognitive deficits experience visual hallucinations, typically with no other sensory hallucinations. Although few isolated case reports of CBS from India have been published, the prevalence for CBS in India is largely unknown. The primary aim of this study was to estimate CBS prevalence in patients with vision impairment visiting a tertiary eye care center. Methods: The study was conducted in two phases. In phase 1, patients with VI, age ≥40 years with presenting visual acuity worse than 20/63 were enrolled. In phase 2, patients with presenting visual acuity worse than 20/63 and/or with binocular visual field loss, age ≥18 years were recruited. A CBS survey was administered only to those who passed a screening test for cognition impairment. Results: A total of 218 patients were screened (phase 1 = 113 and phase 2 = 105). Two-hundred ten patients (mean age ± standard deviation = 49.2 ± 17.3 years, males = 139) were found eligible to complete the CBS survey. Fourteen patients were found to have visual hallucinations. In addition, three other patients had visual hallucinations with associated auditory input to the visual imagery. All patients had complete insight about their hallucinations. Conclusion: Depending on the inclusion criteria, we found the prevalence for CBS in patients with VI to vary between 6.7% to 8.1% (if including patients with auditory input). More investigation is needed to assess the associated role of other sensory inputs (e.g. auditory) with the visual imagery experienced in CBS.