Published in Neuro

The Ophthalmologist's Map to Charles Bonnet Syndrome

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Discover strategies ophthalmologists can employ to manage Charles Bonnet syndrome, which causes visual hallucinations in patients with significant vision loss.
The Ophthalmologist's Map to Charles Bonnet Syndrome
Charles Bonnet syndrome (CBS) is a phenomenon in which an individual with poor vision begins to see images that do not exist—visual hallucinations. These visual hallucinations can often be confused for a mental illness or psychosis, and patients may visualize various patterns, nature, objects, and even people.1 Patients with CBS tend to only complain of visual disturbances, as they cannot smell, hear, or touch these images. However, these images may be recurrent and complex to describe.

What is the origin of the name?

The CBS eponym was derived from Charles Bonnet, a Swiss philosopher and writer. In 1760, Bonnet's grandfather accrued vision loss after bilateral cataract surgery. Shortly afterward, his grandfather reported seeing random "visions." These "visions" were described to Bonnet as being patterns, buildings, and people. Charles Bonnet deemed his grandfather's visual hallucinations mere "fictions" of the brain.1

His grandfather was cognitively sound and intact, and realized that these hallucinations were not real.

Ironically and unfortunately, Charles Bonnet also experienced similar visual hallucinations later in his life as his vision deteriorated. In 1967, another Swiss scientist, George De Morsier, eventually named these complex visual hallucinations in the setting of severe visual impairment as Charles Bonnet syndrome.2

Case report: Charles Bonnet syndrome

A 100-year-old white female presented to the eye clinic with complaints of recent onset visual hallucinations. She claimed she saw three young children, including a smaller boy who was persistently hopping around, next to two girls. She described them as well-dressed and looking "cute." She then related that occasionally she saw herself walking with these children but knew they were not real. She also stated she was unafraid of these images and believed that the children were there to "protect" her and watch over her.
The patient's previous ocular history included end-stage glaucoma in both eyes. She used timolol 0.5% BID and latanoprost 0.005% QHS in both eyes as treatment. She had selective laser trabeculoplasty in both eyes in the past. One year ago, her visual acuity was 20/80 OD and 20/400 OS. However, on today's visual acuity reading, she could only recognize hand motion when seeing out of the right eye and could only count fingers when seeing out of the left eye. There is no reported history of psychiatric illness or of hearing voices. Additionally, the patient was oriented to time, place, and person.
Her intraocular pressure was recorded at 15mmHg OD and 16mmHg OS. The patient's slit lamp exam was unremarkable, and she was pseudophakic in both eyes. Also, both optic nerves showed cup-to-disc ratios of 0.9. The fundus in the left eye was unremarkable except for macular mottling and a few small scattered drusen. The right eye fundus showed the typical "blood and thunder," as seen in a central retinal vein occlusion (CRVO).
What was the cause of this patient's visual hallucinations?
New onset CRVO, in the setting of advanced glaucoma, causing Charles Bonnet syndrome.
Figure 1 illustrates the fundus exam of the patient's right eye.
Fundus exam CBS
Figure 1: Image provided by authors.

Current theories explaining Charles Bonnet syndrome

While CBS cannot be explained as resulting from a mental illness, other theories try to explain this phenomenon.
  1. Phantom-Vision Theory (deafferentation theory) suggests that a lack of sensory input due to severe vision loss causes spontaneous visual cortex activity, resulting in visual hallucinations.3,4
  2. Release Theory claims that sensory deprivation, in this case, vision loss, may lead to a release of subconscious perceptions.3,4 These perceptions are known as engrams, which are physical and chemical changes that occur to help with new memory associations.5 This theory states that correcting a patient's vision may stop the visual hallucinations.
  3. Irritative Theory claims that spontaneous electrical discharges from the brain's visual cortex cause hallucinations; however, there has not been much research or results in neuroimaging that can validate this theory.3,4
  4. Neuromatrix Theory says that CBS may be due to a network of neurons imparting a pattern when visual information is received, such as a "neuro signature."3,4 This theory also states that any change in a human's sensory input will modulate that person's sensory output, potentially leading to hallucinations.3,4

Presentation of Charles Bonnet syndrome

Patients diagnosed with Charles Bonnet syndrome have variable and stereotypical presentations. Some of the images these patients see may last for seconds to hours, and the frequency of episodes can range from some happening every few days to others lasting for multiple years.3,4
The most common presentation of visual hallucinations is seeing people, but images of animals, places, simple patterns, colors, or even hallucinations in black-and-white have also been reported. CBS patients describe the images as static or dynamic and may also report seeing images of themselves—known as autoscopia.6
The average age of incidence of CBS is between 75 and 80 years, however, this syndrome has been reported in younger patients as well. The prevalence of CBS ranges between 0.4% and 30%.7 This wide range in prevalence was attributed to a combination of patient reluctance to disclose their hallucinations and physician misdiagnosis.7

Potential triggers for Charles Bonnet syndrome

Specific triggers can cause and exacerbate CBS, including but not limited to fatigue, stress, low levels of illumination, general sensory reduction, and social isolation.

Various medical conditions may affect the part of the brain that deals with visual hallucinations.

Parkinson's disease, Alzheimer's, mental illness, and strokes are just a few conditions that may cause an individual to have visual hallucinations.1 However, it is vital to recognize that there is no causation between CBS and any of the conditions listed above.

Managing patients with CBS

Many patients may be reluctant to disclose that they are having hallucinations out of fear of being misdiagnosed with a mental illness. Creating a safe and comfortable atmosphere for these individuals to discuss their concerns with their physician and a counselor can be valuable as a coping mechanism.
Dealing with a CBS episode may be frightening and challenging initially, but there are ways to help minimize the hallucinatory effect. Using the techniques listed below may allow patients to alleviate the increasing anxiety surrounding their episodes.
“Inhibitors” for hallucinations caused by CBS include:
  • Opening or closing the eyes
  • Blinking multiple times
  • Turning on a light
  • Looking for a distraction
  • Hitting and shouting at the hallucination

Techniques for addressing specific hallucinations

There are several ways to manage hallucinations when they present in different contexts.1 Hallucination of space are visions that can change the shape of rooms and streets, making ambulation difficult for a person. Reaching out and checking the area around is helpful, as well as using a cane or walking stick.

It has been noted that animal hallucinations are decreased by touching the images of animals seen.

Hallucinations of people are controlled by the understanding that if a person seen in a hallucination is wearing a costume or something other than "normal" clothes, it is most likely not real. Also, being aware of when people are supposed to be visiting a patient's home will help make it easier for the patient to recognize what is real and what is not. Most CBS patients recognize that the images they are seeing are not real.

Is there a treatment for CBS?

The diagnosis code for Charles Bonnet syndrome would fall under "psychophysical visual disturbances." The ICD-10 code to support this diagnosis is H53.16.8, and while there is no definitive treatment for CBS, there are existing treatment strategies.
Treatment strategies for Charles Bonnet syndrome include:3,6
  • Correcting the underlying ocular pathology, including cataract extraction to improve vision and overall brightness perception
  • Optical correction
  • Pharmacological agents, such as anticonvulsants and neuroleptics
  • Social interaction for patients

Takeaways for treating CBS

Patients with CBS recognize that the images they see are not real, even though they are very vivid. CBS only affects sight, so these patients can be reassured if there are no delusions of other senses, such as smell or sound, presently associated with the hallucination. It is also essential to explain to patients the origin of how vision can be affected in the brain.

Understanding the basics will allow patients to see how Charles Bonnet syndrome fits into this context.

Suppose there is a situation in which the visual pathway from the retina to the visual cortex is damaged; in that case, vision loss can occur, and the brain may process images that are unreal to the person. These patterns and images are experienced as hallucinations, which is the hallmark of Charles Bonnet syndrome.1 The best recommendation to rule out any psychiatric illness or related disease is to first speak with the patient's primary care provider (PCP). If no diagnosis is made with the PCP, then CBS could be very likely.
  1. RNIB.ORG.UK. Royal National Institute of Blind People. Understanding visual hallucinations. https://media.rnib.org.uk/documents/Understanding_Visual_Hallucinations_-_CBS_2021.pdf. Published June 2021. Accessed December 6, 2022.
  2. Omnia. (n.d.). Retrieved December 26, 2022. https://www.omnia.ie/index.php?navigation_function=2&navigation_item=/2020903/KKS13187&repid=1.
  3. Schultz G, Melzack R. The Charles Bonnet syndrome: phantom visual images. Perception. 1991;20:809-825.
  4. Cogan DG. Visual hallucinations as release phenomena. Graef Arch Klin Exp Ophthalmol. 1973;188:139-150.
  5. Josselyn SA, Tonegawa S. Memory engrams: Recalling the past and imagining the future. Science (New York, N.Y.). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7577560/. Published January 3, 2020. Accessed December 6, 2022.
  6. Menon GJ, Rahman I, Menon SJ, et al. Complex visual hallucinations in the visually impaired: The Charles Bonnet syndrome. Surv Ophthalmol 2003;48: 58-71.
  7. Soofi T, Mackner A, Skorin L. Why is this patient having visual hallucinations? J Am Acad Phys Assist. 2018;31(1):55-56. doi:10.1097/01.jaa.0000527712.46439.63.10
  8. ICD10data.com. 2023 ICD-10-CM diagnosis code H53.16.10. https://www.icd10data.com/ICD10CM/Codes/H00-H59/H53-H54/H53-/H53.16.  Accessed December 6, 2022.
Mohammed Zaman
About Mohammed Zaman

Mohammad Zaman is a medical student at the Arkansas College of Osteopathic Medicine. He is a graduate of Illinois State University with a bachelor's degree in exercise science.

Mohammed Zaman
Leonid Skorin, DO, OD
About Leonid Skorin, DO, OD

Dr. Skorin is a Consultant in the Department of Surgery, Community Division of Ophthalmology at the Mayo Clinic Health System in Albert Lea, MN and is an Assistant Professor of Ophthalmology, Mayo Clinic College of Medicine in Rochester, MN.

Leonid Skorin, DO, OD
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