An 84-year-old woman, who has advanced atrophic age-related macular degeneration (AMD) and disciform scarring, started seeing things a few months ago. Specifically, she continually sees two black Labrador retrievers and three calico kittens. The animals do not make any noise; they just look at her. The woman knows these animals do not exist. She wants to tell her family and doctor about them but decides against doing so. She is afraid that if she tells her family and doctor, they will have her committed.

This patient has Charles Bonnet syndrome (CBS), a condition in which patients experience complex visual hallucinations, often pleasant in nature, that cannot be explained by any disturbance of thought or the presence of a psychiatric disorder.1-3


CBS affects 12% to 15% of visually impaired patients, yet the condition often goes undiagnosed.4 There are two reasons for this: Patients, such as this one, are reluctant to tell anyone about these hallucinations for fear of being labeled crazy or insane. Also, many doctors lack awareness of this condition.2

As primary-care clinicians, we can educate ourselves and our patients (particularly those who already have or are at risk for CBS) about the condition. This, in turn, may make patients who have CBS less reluctant to tell us about their visual hallucinations. Here, we will discuss the epidemiology and history of CBS, its pathogenesis, diagnosis and management.

Epidemiology
CBS most often occurs in elderly individuals who are usually mentally healthy.5 Patients are always fully aware that the visual hallucinations they experience are not real.6

The mean age of incidence is about 57 to 80, but CBS also has been reported in children who have rapid vision loss.2,7 The predilection for the elderly merely reflects the increased incidence of sudden, profound vision loss in that age group.2 Although most CBS patients have vision loss, this is not required to diagnose the condition.5

We use the term Charles Bonnet Plus (CBS Plus) to describe clinical cases in which visual hallucinations are associated with other cognitive, psychopathologic or neurological disorders.8 Patients who have CBS Plus have cognitive impairment, while CBS patients are wholly mentally intact. The difference between CBS Plus and mental illness is that patients who have CBS Plus have both cognitive and visual deficits that contribute to their state of sensory deprivation.

The History of CBS
CBS is named after Charles Bonnet (1720-1793), a Swiss naturalist, biologist and philosopher who was the first person to use a scientific approach in the study of hallucinations and related phenomena.3

Charles Bonnet was the first person to use a scientific approach in the study of hallucinations and related phenomena.

In 1760, he published a book, Essai analytique sur les facults de lame which translated to English means an analytical essay on the blade faculties. The book summarily described his 89-year-old grandfathers experience with hallucinations. Dr. Bonnets grandfather, Charles Lullin, experienced substantial vision loss and reported seeing subjective, vividly clear images of men, women, birds, carriages, buildings and other things a decade after he underwent bilateral cataract surgery.9 These images appeared and disappeared, approached and receded, and increased or decreased in size, Mr. Lullin reported. None of the images were accompanied by sound, he said.10

Mr. Lullin, a magistrate, remained cognitively intact and fully realized that his visions were fictions of his brain.2,11 He told his grandson that he was not frightened by these images but rather intrigued and amused by them.3,12 Ironically, Dr. Bonnet also experienced these visual hallucinations as his own vision worsened near the end of his life.1,6 (No source can be found that reveals the cause of Bonnets visual deterioration.)

Pathogenesis
Bilateral simultaneous or sequential vision loss from any cause can result in visual hallucinations. (See A Look at Visual Hallucinations) AMD is the most com-mon triggering pathology of CBS, although it also has been associated with pathology at any level of the visual system.12,13 This includes any condition that affects the visual pathway from the eyeball, optic nerve and visual radiations of the brain to the occipital cortex. These visual hallucinations are often referred to as release hallucinations because they arise from or are released in a visual cortex that no longer receives the incoming visual sensory impulses that usually filter out nonvisual stimuli.14

This release phenomenon is part of the sensory deprivation theory that explains CBS.12,15 The vision loss produces a state of relative sensory deprivation that allows these images to be released into conscious perception.16 This theory has also been called the phantom-vision theory and has been compared with phantom-limb syndrome. Phantom-limb syndrome occurs in a patient who experiences sensory sensations, such as burning at the soles of her foot, even though her leg was amputated.2,16,17

Cortical input from other areas of the brain, such as memory association areas, also may fill in for the lack of sensory input from the eyes. Indeed, CBS patients who undergo vision-restoring surgery (cataract surgery, macular translocation, etc.) no longer experience visual hallucinations.12,18-20

The degree of visual impairment is important in the formation of these release hallucinations. CBS occurs more frequently in patients who have a higher degree of visual impairment and bilateral pathology.2,19,20 Patients do not experience unilateral hallucinations unless they perceive the images more in one eye than in the other. Release visual hallucinations usually occur in patients who have a visual acuity of 20/60 or worse in the better eye.2,19,20

Most visually impaired individuals do not experience visual hallucinations. The reason for this is not known.21 Also consider individuals who live alone or experience other forms of social isolation. These circumstances reduce external sensory stimulation, which in turn, is conducive to forming visual hallucinations in some visually impaired individuals.16,22


A Look at Visual Hallucinations
Visual hallucinations generally are defined as a visual experience based on endogenous neural activity rather than on exogenous viewed objects.12 Patients subjectively experience a visual event although no external objective stimuli are present.22

Patients who experience visual hallucinations report seeing stimuli as if the stimuli truly exist.1 These patients are awake and see something that others in the same environment do not see.29 As with pain, paresthesia and other sensory complaints, we cannot verify visual hallucinations.29

If visual hallucinations are accompanied by hallucinations of other sensory organs, such as auditory hallucinations, you should suspect a major mental illness.6 In one study of 100 patients who had chronic schizophrenia, 32% experienced auditory hallucinations, and nearly every patient who experienced visual hallucinations also experienced auditory hallucinations.30 The term pseudohallucination describes patients who are completely aware that their sensory experience is unreal.2

Two Categories
Visual hallucinations fall into two categories: unformed and complex. Unformed visual hallucinations, also known as elementary hallucinations, phophenes or photopsias, are the most common of all visual hallucinations and usually originate from within the eye.31 They consist of colored or colorless bright lights, such as points, flashes, stars, sparks, spots or streaks.2 Phosphenes that take the shape of lightning are known as Moores lightning streaks. These likely result from traction of the vitreous on the retina.29,31 

Another unformed visual hallucination: alterations in a patients color perception. These include:

Xanthopsia, or yellow vision. This is the most common change of color vision.29 Xanthopsia may occur in patients who use digoxin and digitoxin. It occurs in about 80% of patients who have digoxin intoxication (the experience of nausea, vomiting, abdominal discomfort and cardiac arrhythmias) but can also be detected in individuals who are at therapeutic drug levels.32

Cyanopsia or blue color changes. These can occur with systemic use of amphetamines, chloroquine, digitalis, nalidixic acid, oral contraceptives and medications used to treat erectile dysfunction.31 Patients who undergo cataract surgery and intraocular lens implantation may initially report seeing a blue tint on and around objects. The natural crystalline lens with a cataract absorbs the blue light. Then, the IOL lets the full spectrum of light in, and the patient now sees the blue light (which was previously blocked) as an exagerrated perception.

Erythropsia, or a reddish tint. This may occur in patients who use atropine, ergotamine and various sulfa drugs. Hemorrhages in the anterior chamber, vitreous or retina may also cause erythropsia.31

Less common color distortions. These include chloropsia (green vision), ianthinopsia (violet) and brunescence (brown). Chloropsia and ianthinopsia occur secondary to digitalis toxicity, while brunescence most often occurs in patients who have advanced cataracts. Cataract patients can experience either hallucinations or illusions depending on how significantly their vision is affected.

Complex, or formed visual hallucinations involve images of objects or persons that may be related to the patients past experiences.13 Formed visual hallucinations may occur after extensive visual field loss, even when central visual acuity is preserved.16 In one study, up to 62% of patients with homonymous hemianopsia and formed visual hallucinations were not aware of their visual loss in the blind hemifield (hemianopic anosognosia).33 Patients who experience new-onset visual hallucinations should undergo formal visual field testing.33

Other Phenomena
An hallucination is the visualization of something that is not in the environment. An illusion is a misinterpretation of what one is seeing in the environment. Hallucinations occur in those who have a very severe decline in visual acuity. Other visual phenomena include altered perceptions of a viewed object. For example, patients might mistake a rope for a snake or polka dots on a dress for insects.12,34,35 Patients who have altered sensory experiences, whether illusory or hallucinatory and believe the images they see are real, suffer from delusions.12 This perception of reality, especially if accompanied by non-visual sensory phenomena (e.g., auditory hallucinations) is a sign of psychosis.6

Palinopsia is a unique type of visual illusion in which patients see a previously viewed scene suddenly played back before their eyes.12 There are at least two forms of palinopsia: immediate and delayed.14 With the immediate form, an image persists after the actual scene disappears. This usually fades after several minutes. With the delayed form, an image of a previously seen object reappears after an interval of minutes to hours; this sometimes occurs repeatedly for days or even weeks. This type of delayed palinopsia may be considered a hallucination rather than an illusion.12

Palinopsia is also known as visual perseveration.22,14 The recurrent images may occupy all or only a part of the visual field and most often are seen in a blind or reduced-acuity hemifield.15 In some patients, palinopsia is part of a focal seizure, while lesions of the right posterior hemisphere cause this phenomena in other patients.12,14,15 L.S.


Diagnosing CBS
There are several diagnostic criteria for CBS, namely the occurrence of visual hallucinations in elderly, mentally healthy individuals.5 These visual hallucinations are:

Detailed, clearly focused images and are sometimes colored. They either move through space or remain stationary.16,21,23

Gradual and increase in frequency. More often, however, a sudden onset of hallucinations occurs several times a day.16 There does not appear to be any common trigger; although fatigue, stress and dim or bright light are significant triggers in some patients.20,24

Appearing off and on for days, months or even years.5,9,16 They tend to disappear as the patient loses vision completely, though they may remain even as the patient becomes totally blind.11

Typically involving neutral or pleasant emotional reactions.16,21,23 Any type of image can be seen, but the most common one is that of a human.12 Some patients report different hallucinations with each episode, while others see the same image each time.7 Patients usually do not recognize the people in their visions; although some will perceive images of themselves, possibly at an earlier stage in their lives. This type of imagery is known as heautoscopia.2

Dry atrophic macular degeneration in an 84 year-old woman diagnosed with CBS.

There is no evidence that patients who have CBS have delirium or dementia or that the patients visual images have a negative impact on intellectual capacity. There is also no evidence of deterioration as in the affective syndromes, such as chronic depression, paranoid developments, psychosis, intoxication or neurological disease.5

Also, the patient should not experience other delusions or hallucinations of the other senses.16,21,23 Interestingly, elderly patients who develop hearing loss may exhibit a similar phenomenon to CBS known as musical hallucinations, but this type of hallucination is much more rare.25

Loss of vision due to ocular disease is a specifying factor in most cases of CBS, but it is not obligatory for diagnosis.5 Because auditory hallucinations can occur, the coexistence of hallucinations of other modalities does not preclude a diagnosis of CBS, provided subjects are aware that their experiences are unreal.26

Management
The most critical management strategy for CBS is reassurance and counseling patients and their families or caregivers. Once patients understand that they are not crazy or going insane, the hallucinations usually do not bother them anymore. Patients more readily accept the hallucinations, and some patients even report enjoying these visions.14

For most patients, the visual hallucinations will likely disappear spontaneously, either with improvement or further deterioration of visual function.27 Even among patients who have no further vision change, hallucinatory episodes tend to occur less frequently over time.16

Pharmacotherapy has not been shown to be especially effective for patients who find the hallucinations annoying, upsetting or distracting.2 However, the anticonvulsants carbamazepine, clonazepam and valproate sodiumalong with the neuroleptics (antipsychotic drugs) thioridazine hydrochloride and haloperidolhave been used with some success.2

Moving patients into a more stimulating environment, keeping them socially involved and busy with hobbies and activities also can lessen the hallucinations.14,28 Surgical procedures that maximize the patients visual acuity (e.g., cataract surgery), meticulous refraction or low-vision aids can also be helpful.2

By educating ourselves about the history, pathogenesis, diagnosis and management of CBS, we can educate those who may have CBS or are at risk of developing it. And, we can ensure that patients will confide in us rather than hide in fear.

Dr. Skorin is the staff osteopathic ophthalmologist at Albert Lea Eye ClinicMayo Health System, Albert Lea, Minn.

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Vol. No: 142:10Issue: 10/15/2005