New Research: Rethinking Charles Bonnet Syndrome and Visual Hallucinations

British Journal of Ophthalmology logo

Charles Bonnet (“Bo-NAY”) Syndrome (CBS) is a condition that causes vivid, complex, recurrent visual hallucinations, usually in older adults with later-life vision loss from eye conditions that can include macular degeneration, diabetic retinopathy, and glaucoma.

The visual hallucinations associated with CBS can range from animated, colorful, dreamlike images to less complicated visions of people, animals, vehicles, houses, and other everyday items. By some estimates, as many as 20-30% of adults with vision loss are affected by CBS, although actual numbers are difficult to determine, since few people who experience these symptoms are likely to discuss them with family members, friends, or physicians.

It is thought that these hallucinations are relatively benign and begin to recede in approximately 12-18 months, after the brain adjusts to the individual’s vision loss.

A new study from the United Kingdom, however, has shed new light on CBS, indicating that CBS hallucinations may last far longer (five years or more) and have more serious psychological consequences than previously acknowledged.

The study also suggests that there may be significant discrepancies between established medical opinion and the realities of CBS.

The British Journal of Ophthalmology

The study, entitled Negative Outcome Charles Bonnet Syndrome, has been published online as an Open Access article in the May 13, 2014 edition of the British Journal of Ophthalmology (BJO). The authors are Thomas M. Cox and Dominic H. ffytche, who represent the Department of Old Age Psychiatry, Institute of Psychiatry, King’s College London, UK.

About Charles Bonnet Syndrome

Who Was Charles Bonnet?

engraving of Charles Bonnet in profile

Charles Bonnet (March 13, 1720 – May 20, 1793) was a Swiss naturalist and philosopher and the first person to describe the syndrome.

Initially, he observed symptoms of the syndrome in his 87-year-old grandfather, who was nearly blind from cataracts, yet still “saw” men, women, birds, carriages, buildings, scaffolding, and tapestries before his eyes.

In 1760, Bonnet described his eponymous syndrome, in which he documented a range of complex visual hallucinations that occurred in seemingly psychologically intact persons.

What Is Charles Bonnet Syndrome?

Charles Bonnet Syndrome (CBS) was first introduced into the English-speaking psychiatric literature in 1982. Lighthouse Guild International provides helpful illustrations and a definition of CBS, including an important distinction between CBS visions/illusions and delusions:

[Individuals] who perceive these visions know they’re … mirages, of sorts. That is, the images are illusions, not delusions. The difference is that a person with delusions is convinced that what s/he sees is real. [People] with Charles Bonnet Syndrome may initially second-guess themselves, but ultimately accept that their perceptions have no substance.

In other words, adults with CBS are usually in good mental health and come to understand that these illusions or “hallucinations” are not sensate or “real.” In addition, the illusions associated with CBS are usually solely visual and do not occur in conjunction with the other senses (hearing, smell, taste, or touch).

What Causes Charles Bonnet Syndrome?

CBS is sometimes referred to as “phantom vision” syndrome, and can be compared to “phantom limb” syndrome, in which an individual can continue to receive sensation – and even pain signals – from a limb that has been amputated. Similarly, in CBS, when retinal cells no longer receive and relay visual images to the brain, due to eye disease or damage to the optic pathways, the visual system begins creating its own “phantom” images.

More about the Study

From Better education needed on sight loss hallucinations at The Macular Society:

The research, published online by the British Journal of Ophthalmology, documented the experiences of 492 visually impaired people who had experienced visual hallucinations. They suggest there is a serious discrepancy between medical opinion and the realities of the condition.

The phenomenon, known as Charles Bonnet Syndrome, is widely considered by the medical profession to be benign and short-lived. However, the research shows that 80% of respondents had hallucinations for five years or more and 32% found them predominantly unpleasant, distressing and negative.

The study described this group of people as having “negative outcome Charles Bonnet Syndrome.” The group was more likely to have frequent, fear inducing, longer duration hallucinations, which affected daily activities. They were more likely to attribute hallucinations to serious mental illness and were less likely to have been warned about the possibility of hallucinations before they started.

Of respondents, 38% regarded their hallucinations as startling, terrifying or frightening when they first occurred and 46% said hallucinations had an effect on their ability to complete daily tasks [and] 36% of people who discussed the issue with a medical professional said the professional was “unsure or did not know” about the diagnosis.

Dr. Dominic ffytche, clinical senior lecturer at King’s College London’s Institute of Psychiatry who led the research said, “With no specific treatments for Charles Bonnet Syndrome, the survey highlights the importance of raising awareness to reduce the distress it causes, particularly before symptoms start. All people with Charles Bonnet Syndrome are relieved or reassured to find out about the cause of their hallucinations and our evidence shows the knowledge may help reduce negative outcome.”

More from the British Journal of Ophthalmology

From the article abstract:

Methods: 4,000 members of the Macular Society were sent a structured questionnaire covering the phenomenology of CBS, its prognosis and impact, symptom reporting, patient knowledge and sources of information.

Results: 492 people with CBS were identified. Kaplan–Meier analysis suggested 75% had CBS for 5 years or more. Thirty-two per cent had negative outcome. Factors associated with negative outcome were: (1) frequent, fear-inducing, longer-lasting hallucination episodes, (2) one or more daily activities affected, (3) attribution of hallucinations to serious mental illness, (4) not knowing about CBS at the onset of symptoms. Duration of CBS or the type of content hallucinated were not associated with negative outcome.

Conclusions: CBS is of longer duration than previously suspected with clinically relevant consequences in a third of those affected. Interventions that reduce the frequency, duration or fear of individual hallucination episodes and education prior to hallucination onset may help reduce negative outcome.

VisionAware will provide updates of Charles Bonnet Syndrome research as they become available

Additional Information

Charles Bonnet image source: Wikimedia Commons. This image is in the public domain because its copyright has expired.