The eponym Charles Bonnet syndrome (CBS) refers to the occurrence of formed visual hallucinations in older persons with normal cognition and insight. In 1760, the Swiss naturalist first described the syndrome in his grandfather, who had dense cataracts. Charles Bonnet syndrome has since been described in association with various pathologies leading to deterioration of vision at all levels of the visual system, such as in ocular pathology (e.g., cataract 1 and age-related maculopathy 2–4), optic nerve pathology in glaucoma 5,6 and temporal arteritis, 7 or secondary to pituitary tumor 8 and cortical damage. 9
The prevalence of CBS associated with these ocular pathologies is not clear. Several studies have reported CBS to be rather prevalent (approximately 12% to 13%) in patients with age-related macular degeneration. 2,4 Glaucoma may also lead to severe deterioration in vision, therefore one would expect to frequently encounter CBS among patients with glaucoma. However, aside from isolated descriptions of glaucoma patients with visual hallucinations, 5,6 this phenomenon is not well documented, and its prevalence is unknown.
We thus sought to study the prevalence of CBS in glaucoma patients with decreased vision who were attending an outpatient clinic in a tertiary care medical center, and to characterize the nature of these phenomena.
The population screened consisted of patients visiting the Glaucoma Clinic at the Department of Ophthalmology, Sapir Medical Center, during a period of 10 months. All patients with visual acuity of 20/80 or less in both eyes were included in this cross-sectional study. Each patient was questioned about whether he or she had experienced the occurrence of certain formed sights that were unreal. Those who responded positively were asked to describe their experiences in detail. Patients were included in the study only when the interviewer was convinced that the sight perceived by the patient was not a distorted figure, an entoptic phenomenon, a dream, or an unclear shadow of an actual object.
A thorough interview was then carried out relating the characteristics of the hallucination. The size, color, clearness, state of motion, content, frequency of appearance and duration, and area of appearance in the visual field were all documented. Data were collected regarding age, sex, ethnic origin, level of education, living situation, medical history, neurologic and psychiatric history, and substance abuse. The cognitive status of the patients was crudely estimated by an abbreviated Mini-Mental test. 10 Each patient underwent a complete ocular examination that included Snellen visual acuity measurement, applanation tonometry, slit lamp examination of the anterior segment, and a dilated fundus examination.
Eighty-nine patients met the inclusion criteria. Eleven patients (12.3%) admitted to having experienced visual hallucinations, and their characteristics are described in Table 1. Eight of these patients were male and three patients were female, and the mean age was 74 years (range, 60–96 years). The number of years of formal education varied from none to 15 years (mean, 7 years). None of the patients was taking a medication with hallucinatory potential. Except for one patient who was living in a nursing home, all patients were living either with a spouse (eight patients) or their family (two patients). Although almost all patients lived with a spouse or family member and half of patients experienced these hallucinations over a period of 1 year or more, only one patient (patient 11) had previously shared this experience of visual hallucinations with another person. In fact, when the patients were questioned about this experience, often the spouse that was present in the room immediately rejected such a possibility and was surprised to hear differently. However, most patients seemed to be relieved once they could finally share this experience without feeling ashamed and insecure about it.
The type of glaucoma and the additional relevant ocular findings for each patient are elaborated in Table 2. Except for two patients, all had at least one additional major ocular finding that could have contributed to the reduction of vision. Four patients had cataracts and three patients had suffered from central vein occlusion. A maculopathy was present in five eyes. Other vision-reducing findings were anterior ischemic optic neuropathy in one eye and a corneal opacity in another.
All patients were aware of the unreal nature of their hallucinations and rejected the possibility that they had misinterpreted a blurred image because of low vision. The contents of the visual hallucinations of each patient are described in Table 3. Though most patients had one repeatable sight, three experienced more than one sight. Patient 1 had four different hallucinations, each of which he was able to describe in detail. Although the visions were sharp for most patients, the figures were not always complete. Patient 1 saw only the head of an old man, patient 3 noted that the woman's face was blurred, and patient 5 described only the upper part of the body of the people that he saw. In some cases the sight was still, whereas in others the figures or objects were moving. However, in most cases there was no interaction between the vision and the patient except for two patients. Patient 3 described a vision of a woman dancing in front of him and approaching him fondly (to the dismay of his wife), and patient 9 saw a balloon moving away from him when climbing the stairs.
The size, color, frequency, and duration of the hallucinations are described in Table 4. The frequency of the hallucinations varied between daily and weekly, though three patients had a single episode. The figures and objects seen by the patients were not always of normal size. Some described abnormally large figures whereas others noted abnormally small, even “dwarf-like” figures. Although most hallucinations were chromatic, some were monochromatic or achromatic. For most patients the length of time of a single hallucination was estimated as 1 or 2 minutes. One patient estimated the time in seconds, and only one patient claimed that the vision lasted 30 to 60 minutes.
Twelve percent of our glaucoma patients with low vision admitted that they had experienced visual hallucinations. These results are in agreement with the report of an 11% prevalence of CBS among patients attending low vision clinics, 5 and a prevalence of 12% and 13% among patients with age-related macular degeneration 2,4 screened for visual hallucinations.
Formed visual hallucinations are not rare among patients with vision abnormalities. However, reports of their occurrence in the ophthalmologic literature are scarce. 4,11,12 Presumably, many of the patients are referred to psychogeriatric units for evaluation. Studies discussing CBS relate to patients recruited at these clinics, 13 and are published in neurologic, 14 geriatric, 15 and psychiatric 16 journals. Even studies surveying patients with low vision who were recruited in ophthalmology departments have been published in psychiatric literature 5,17; thus, many ophthalmologists are unaware of the relatively high prevalence of this phenomena among their patients with low vision.
Several neurologic diseases such as epilepsy, 18 Parkinsons disease, 19 and dementia 20 have been associated with visual hallucinations, but none of these was detected in our patients. Likewise, cerebral strokes have been associated with visual hallucinations. 9 Among our patients, only patient 3 suffered repeated strokes and an association between that occurrence and the hallucinations can be argued in that particular case.
Several ocular pathologies have also been described in association with visual hallucinations. 1–6 In our group of patients, five had macular pathology in addition to advanced glaucoma. It is impossible to estimate the relative contribution of the maculopathy to the overall low vision state in these patients. Dense cataracts were present in two patients. In one of these patients (patient 9), hallucinations ceased after the removal of the cataract and improvement in visual acuity.
An impaired cognition should be excluded before making a diagnosis of CBS. Many studies have incorporated psychologic tests into their routine evaluation of patients with complex visual hallucinations. 15 In our study we used an abbreviated form of the Mini-Mental State Examination. 10 None of our patients had impaired cognition.
The content and characteristics of the hallucinations in CBS were described by Schultz et al. 21 In their 60 patients, visual hallucinations were present for a few seconds and no motion occurred. The images were sharp, appeared and vanished suddenly, and were only present when the eyelids were open. In our group of patients, hallucinations were present for a longer period and images were in motion in some cases.
The pathogenesis of visual hallucinations in mentally healthy persons is unclear. Sensory deprivation has been implicated as a possible cause. 12 The reaction of the visual cortex to the sudden or progressive lack of visual stimulation results in release phenomena (i.e., the perception of nonexisting images). 22 Sensory deprivation is thought to be more prevalent in patients with decreased social contacts and low extroversion. 23 Thus, living alone has been implicated as a predisposing factor for the development of visual hallucinations. This factor was not relevant in our group of eleven patients because 10 were living with a spouse or family member.
An alternative approach to explaining the pathogenesis of CBS has regarded the condition as an irritative (ictal) phenomenon 18 secondary to epilepsy or cerebral space-occupying lesions. However, none of our patients had evidence of such lesions or a history of epilepsy.
Recently it has been suggested that different abnormal perceptions originate in different specialized cortical areas. 24,25 The functional magnetic resonance imaging has been instrumental in investigating this association. 26 In particular, the technology associated the ventral extrastriate region of the human brain with color perception and suggested that in some patients with CBS, a phasic increase in activity in this area was associated with chromatic hallucinations often reported as vivid. 27
Treatment for CBS is rarely needed unless patients are disturbed by the frequent occurrence of sights. Treatment with classic neuroleptics, antidepressants, or benzodiazepines is generally ineffective. Successful therapy has been observed with melperone 28 and carbamazepine. 29 Recently there have been reports of successful elimination of the hallucinations with cisapride, a potent 5-hydroxytryptophan antagonist. 30 In our group of patients, the occurrence of hallucinations was of no concern after the physicians explained their source and nature. Thus, no patient required treatment.
Our study suggests that CBS is not rare in glaucoma patients with low vision. Because patients tend to conceal this phenomena and rarely consult their ophthalmologists about these experiences, we recommend that all patients with low vision be questioned about occurrence of visual hallucinations. Undoubtedly, a discussion of these phenomena with the patients and assurance of their harmless nature will reduce the anxiety and shame associated with having visual hallucinations.
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© 2001 Lippincott Williams & Wilkins, Inc.