The rarity of Charles Bonnet syndrome Yasuko Shiraishi a , Takeshi Terao a, *,KenjiIbi b , Jun Nakamura a , Akihiko Tawara b a Department of Psychiatry, University of Occupational and Environmental Health School of Medicine, Kitakyushu, Japan b Department of Opthalmology, University of Occupational and Environmental Health School of Medicine, Kitakyushu, Japan Received 11 November 2002; received in revised form 7 May 2003; accepted 11 June 2003 Abstract Charles Bonnet syndrome (CBS) is characterized by complex visual hallucinations in otherwise psychologically normal people. Estimates of the prevalence of CBS in different samples vary from a small percentage (around 1%), to a relatively large percen- tage (about 10%). The purpose of the present study is to determine whether CBS is rare or not. One-thousand ophthalmologic and optometric outpatients at a university hospital were consecutively screened by a questionnaire to identify patients possibly experiencing visual hallucinations. The mean corrected visual acuity in the best eye was 1.1. Those who positively responded to the questionnaire were further investigated to determine whether their symptoms were consistent with CBS. As a result, the pre- valence of CBS was 0.5% (5/1000). In subclass analyses, the prevalence was 3 of 372 (0.8%) in the low vision group, 2 of 346 (0.6%) in the elderly, and 1 of 120 (0.8%) in both conditions. These were not significantly different from each other or from the overall prevalence (0.5%). This low prevalence of CBS in our subjects may be due to their relatively good visual acuity because previousstudieswithhighprevalenceofCBSinvestigatedpatientswithavisualacuityoflessthan0.3.TheprevalenceofCBSmay be low in patients with these particular characteristics, and this syndrome seems to be rare in even ophthalmologic and optometric patients if they do not have seriously low vision. Further studies are needed to investigate the prevalence of CBS in general population. # 2003 Elsevier Ltd. All rights reserved. Keywords: Charles Bonnet syndrome; Visual hallucinations; Visual acuity; Advanced age; Prevalence 1. Introduction Charles Bonnet syndrome (CBS) was named after the Swiss Philosopher who first described the occurrence of vivid complex visual hallucinations in his visually impaired, otherwise psychologically normal, grand- father Charles Lullin in 1760 (Damas-Mora et al., 1982).Sincethen,thedisorderhasbeenwidelyreported but estimates of prevalence vary considerably from studytostudyfromaslowas0.4%(Adachi,1996)toas high as 12% (Teunisse et al., 1996). As such, it is pre- sently uncertain whether CBS is rare or not. An explanation for differences in the reported pre- valence of CBS may lie in the different diagnostic cri- teria applied and the samples used to investigate the disorder. There have been five sets of diagnostic criteria (Damas-Mora et al., 1982; Teunisse et al., 1996; Gold and Rabins, 1989; Podoll et al., 1990; Ball, 1991) for CBS and, with the exception of Ball (1991), all included the presence of insight to visual hallucinations; thus ‘‘psychological normality’’ may be at least partially guaranteedinCBSpatients(TeraoandCollinson,2001; Terao, 2002). In addition, the above-mentioned criteria donotrequirethepresenceofopticpathology,although clinicians commonly associate CBS with eye diseases (Fernandez et al., 1997). Thus, low visual acuity is not necessary for diagnosing CBS, but there remains a pos- sibility that in some CBS patients low visual acuity may actually bring about visual hallucinations. In any case, these criteria seem to be relatively consistent in diag- nosing visual hallucinations in otherwise psychologi- cally normal people but have nevertheless been applied to a range of very different samples from ophthalmolo- gic patients to psychogeriatric patients (Terao, 2002). Another possible reason for differences in the repor- tedprevalenceofCBSisthatalloftheabovementioned diagnostic criteria have been derived almost exclusively from cross-sectional observations. It is therefore 0022-3956/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0022-3956(03)00090-6 Journal of Psychiatric Research 38 (2004) 207–213 www.elsevier.com/locate/jpsychires * Corresponding author. Tel.: +81-93-691-7253; fax: +81-93-692- 4894. E-mail address: t-terao@med.uoeh-u.ac.jp (T. Terao).