Charles Bonnet syndrome: low awareness among patients with glaucoma

© Annals of Eye Science. All rights reserved. Ann Eye Sci 2020 | http://dx.doi. org/10.21037/aes-20-115 Charles Bonnet syndrome (CBS) is a benign condition characterised by complex visual hallucinations in individuals with visual impairment (1). Approximately one-third of affected patients suffer from distress as a direct consequence of their hallucinatory experiences (2). The distress is often caused by fear of impending insanity, and may be propagated by lack of awareness and knowledge about CBS (3). The proportion of patients with glaucoma that are familiar with CBS is unknown. Therefore, we sought to investigate this in a population with primary open-angle glaucoma (POAG). Our study was part of a larger, yet unpublished, prospective study of the prevalence and clinical characteristics of CBS in POAG. Patients with a known diagnosis of POAG that had visited the glaucoma clinic at Skåne University Hospital in Malmö, Sweden, between April 1st 2018 and December 31st 2018 were included. We excluded patients with concurrent neurological and/or psychiatric disorders, or other known causes of vision loss, e.g. latestage age-related macular degeneration. We explored the patients’ precursory knowledge of CBS using the question (translated to Swedish): “Some patients with poor eyesight see things which they know are not there. These hallucinations occur on repeated occasions and are described as being vivid and complex, e.g., persons, animals, flowers, or patterns. This phenomenon is known as Charles Bonnet syndrome. Have you ever heard or read about this? ” in a written questionnaire (4). Patients responding affirmatively were contacted and further interviewed. Results from the patients’ visual acuity (VA) examinations and automated visual field tests were obtained from the medical records. The results closest in time to when the patient had responded to the questionnaire were chosen. Best corrected visual acuity (BCVA) was tested in both eyes using an electronic Snellen chart, and the automated visual field test 24-2 or 30-2 was conducted using the Swedish interactive thresholding algorithm on the Humphrey Field Analyser (Carl Zeiss Meditec, Dublin, CA, USA). Patients with suspected CBS also underwent objective examination of both maculae using Swept Source Optical Coherence Tomography (Triton, Topcon, Medical Systems, Tokyo, Japan). Statistical analysis was performed using the SPSS software (version 25, IBM, Chicago, IL, USA). For categorical data Fisher's exact test or Pearson’s chi-square test were used when the data sample was small or large, respectively. For continuous non-parametric variables, the Mann-Whitney U test was applied. A significance level of <0.05 was employed. A total of 338 patients with definitive glaucoma, i.e., confirmed glaucomatous visual field defects on at least two consecutive tests, were included in this study. Twelve (3.5%) patients claimed they had precursory knowledge of CBS when answering the written questionnaire. Four (1,2%) of these did, in fact, exhibit prior knowledge of CBS when contacted and interviewed. Two declared knowledge of CBS because a close relative with AMD had experienced visual hallucinations. One acquired knowledge through the Letter to the Editor