Charles Bonnet Syndrome: When Visual Loss Conjures Mischief

This article is from February 2008 and may contain outdated material.

Walter J. Burghardt, SJ, can’t see more than hand motion with one eye or count fingers at three feet with the other. Yet the 93-year-old Jesuit scholar and theologian “sees” a country garden. Sometimes he even sees joggers, rows and rows of them, running through the greenery.

Fr. Burghardt, who lives in Philadelphia, has Charles Bonnet syndrome (CBS), a disorder of visual hallucinations that occurs in cognitively normal persons with severe bilateral visual loss or deafferentation of the visual cortex. In his case, the visual loss is due to neovascular macular degeneration, though any visual impairment can trigger the hallucinatory visions. The more severe the impairment, the greater the chance of having the visual aberrations, which can last seconds, minutes or hours.

“The hallucinations are often genuinely formed and quite vivid,” said Eric Eggenberger, DO, professor of neurology and ophthalmology at Michigan State University. “The patients can tell you minute details about the scenes they’re seeing. It’s almost like a running movie.”

The etiology and the prevalence of CBS are both ill-defined. But everyone agrees that as the population ages, more people will develop the blinding conditions that can result in CBS.

How common? In a review of the literature, Barry W. Rovner, MD, a geriatric psychiatrist who conducts research on depression and AMD, found the prevalence of CBS patients attending ophthalmology clinics ranges from 0.4 percent to 14 percent.¹

Gary C. Brown, MD, director of the retina service at Wills Eye Institute in Philadelphia and professor of ophthalmology at Jefferson Medical College, and Melissa M. Brown, MD, adjunct assistant professor of ophthalmology at the University of Pennsylvania, wrote a paper not yet in print on CBS with Fr. Burghardt. They report that 59 percent of 100 patients they looked at with neovascular AMD saw photopsias in the central visual field—whirly colored or white lights. Another 12 percent had formed visual hallucinations, which in Fr. Burghardt’s case took the form of scenery and joggers. Others have reported seeing flowers, insects, buildings, faces and branching structures.

Etiology Unknown

Charles Bonnet, the Swiss naturalist and philosopher who first described the eponymous condition in 1760 after observing it in his 87-year-old mentally alert grandfather, writes that “all of this appears to have a seat in that part of the brain involved with sight.”²

A failure to communicate. One current theory holds that CBS is most often related to direct damage to the visual system. A contrasting theory is that the images represent release phenomena due to deafferentation of the visual association areas of the cerebral cortex.¹ It’s the same idea as phantom limb syndrome, explained Dr. Rovner, who is professor of psychiatry and neurology at Jefferson Medical College in Philadelphia. “Why would you feel something in your leg, when you have no leg?” Yet some people do. When, for example, the nerve cells that once went to the foot and that continue to be represented in the brain become active, they can lead to the perception that one’s foot is tingling.“If you don’t have the normal input from those nerve cells, then those nerve cells are free to go off on their own direction,” Dr. Rovner explained.

Something similar happens with CBS hallucinations, Dr. Rovner said. Sometimes, when the pathway between the eye and the occipital cortex is interrupted, “those cells or their connections can go haywire, do things on their own, without regard to real stimuli.”

“You’re Not Going Crazy”

While seeing things that aren’t there might sound distressing, most patients report their visions in a nonemotional way. “They’re not distressed,” Dr. Eggenberger said. “Patients describe it more in the realm of a nuisance or a distraction, rather than something that’s driving them crazy.”

Still, the experts agree that it’s important to reassure patients that they aren’t “crazy,” that they don’t have a psychiatric disorder, but, rather, a recognized condition with a name. And since there is no consistently effective treatment or generally agreed upon treatment for CBS, reassurance is often the best—and perhaps the only—thing a physician can do for patients who are seeing things.

“The first thing I tell patients is, ‘This does not mean you’re going nuts. This is a well-known phenomenon.’ It’s your brain making up vision because you can’t see anymore,’” said Karl C. Golnik, MD, professor of neuro-ophthalmology and neurosurgery at the University of Cincinnati and the Cincinnati Eye Institute. After this reassurance, said Dr. Golnik, some patients confess that they were afraid to mention the hallucinations, that they thought they were going mad, even that they feared their children would put them in a nursing home.

Take the initiative. Because fear can prevent patients from mentioning the hallucinations, experts say doctors should initiate the conversation. “I would prefer for physicians, when they have people with severe bilateral visual loss, to educate them that this can occur,” said Dr. Melissa Brown.

Dr. Eggenberger agrees. While it’s not necessary to discuss CBS with every patient, he advised raising the issue with any patient whose visual acuity is 20/100 or 20/200 in both or the best seeing eye. “I couch it in benign terms,” he said, usually by saying, “It is possible that people develop visions when their vision is bad.” Then, rather than the accusatory inquiry, “Are you seeing things?” he prefers, “Are your eyes playing tricks on you?”

Dr. Rovner uses similar phrasing, such as, “Do you ever see anything that other people don’t see?”

Dr. Gary Brown reassures patients that the hallucinations will go away with time. “Sometimes it can take weeks to months. But they do go away.” (See “Mind Over Mirage.”)

Is It CBS or Something Else?

Dr. Eggenberger said a diagnosis of CBS requires ruling out widespread dementia or some other condition that more globally affects cognition.

To make a diagnosis of CBS, he advises looking for the following:

• A normal cognitive exam.
• Absence of psychosis.
• Normal attention level.
• Sufficient visual loss—20/100 or 20/200 in both or the best-seeing eye. Dr. Golnik said that if any of the following are observed, it’s probably not CBS:
• The patient had poor vision for years, but only recently had hallucinations. CBS typically occurs around the time of vision loss.
• The patient has good vision in either eye. A diagnosis of CBS requires poor vision in both eyes.
• Ophthalmologists think about the eyes, but the hallucinations may be a signal of something else going on in the brain. If a patient complains of systemic symptoms such as numbness, tingling, weakness on one side of the body or a new peripheral visual field defect, consider stroke.
• If the patient is not aware that it’s a hallucination and really believes his or her eyes, then that’s a red flag.

Treatment Options

Some patients are extremely bothered by the hallucinations. In that event, medication may be an option. (See “Banishing Bumblebees.”)

Referral to a low vision specialist is another option. Because the hallucinations tend to resolve when vision improves, the patient might benefit from instruction in improved lighting or the use of optical devices.

Dr. Melissa Brown aims for preserving quality of life and mental outlook in these patients. “Even if our patients can’t see well, if we can just let them know that what they’re seeing is an expected phenomenon and not a psychiatric event, then they accept it and their quality of life is greatly enhanced.”

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1 Rovner, B. W. Curr Opin Ophthalmol 2006;6:275–277.

2 Hedges, T. R. Surv Ophthalmol 2007;1:111–114.