Health Talk: Charles Bonnet Syndrome

Hallucinations have always been difficult to explain and interesting to witness. For some, these non-realistic images are seen throughout their day, every day of their lives. Charles Bonnet Syndrome (CBS) is a disorder in which mentally healthy people experience complex visual hallucinations. Patients with this syndrome are usually aware of the unreality of their visual experiences. Their hallucinations are often pleasant, but sometimes can be disturbing.

The patients have little control over these hallucinations, but they are noted to be well-defined, organized, and clear.
This illness was named after Charles Bonnet, a Swiss philosopher who, in 1760, noticed that his nearly blind grandfather was seeing patterns, figures, birds, and buildings that were not actually there. This syndrome affects 10 to 40 percent of people with poor vision. Research suggests that it is more likely to appear in those with visual acuity between 20/120 and 20/400.
This syndrome occurs more often among elderly people and frequently goes unrecognized in a clinical practice.
This could be because, currently, there is little known about the causes of this syndrome and how it correlates with the hallucinations, or how the brain receives information from the eyes to produce these images.

One explanation is that when people lose their sight, their brains are not receiving as many images as needed. To compensate for the loss of visual stimulus, the brain will sometimes release fantasy pictures or old pictures to fulfill that need.
This is comparable to another medical phenomenon, phantom limb syndrome. In phantom limb syndrome, when people’s limbs are missing, the limb’s nerves are still active and sending signals to the brain, which the brain interprets as signals from the missing limb.

It is important for people to understand that Charles Bonnet Syndrome is not actually a mental disorder, but rather that it is simply a side effect of vision loss. Mogk et al., in an article in the journal Vision Rehabilitation: Assessment, Intervention and Outcomes, describe ways to differentiate between mental disorders and side effects of loss in vision.

If the hallucinations occur while the patient is fully conscious, or if patients know they aren’t real and they suddenly disappear, then these are solely visual problems. Another criteria is that the hallucinations must simply be amusing and not grotesque.
CBS, though, could be aggravated by other circumstances such as sensory deprivation, diminished ability, stroke, aging, depression, or bereavement (for instance, seeing deceased kin).

According to a study conducted by Mogk and Mogk, their patients have reportedly seen a wide variety of visual hallucinations. According to research, patients have seen “cartoons, flowers in the bathroom sink, hands rubbing each other, waterfalls and mountains, tigers, maple trees in vibrant autumn foliage, and a dinner party and brightly colored balloons.”

It also seems that these hallucinations usually appear in the same situation each time: For example, one patient would see monkeys around sunset. In this case, the images involving the monkeys stayed for 10 or 20 minutes several times a week over the course of two years. They then began to appear less frequently.

It seems that hallucinatory activity may terminate spontaneously due to factors like improving visual function.
There is no known drug that is effective in preventing the hallucinations, but anticonvulsants have been shown to help.
When people first experience symptoms of Charles Bonnet Syndrome, they are often startled or embarrassed by them. Therefore, specific care such as physician awareness and careful management of the illness is important to the patient’s well-being.

It is also important for the doctor to begin treatment in the form of grief counseling or treatment of psychiatric problems, especially depression, if these conditions worsen the symptoms of CBS.

Since CBS is a side effect of vision loss, treating vision disorders may also help lower incidences of hallucinations. Luckily, most people find their hallucinations to be pleasant or entertaining — seldom disturbing. CBS, therefore, usually does not cause the person to become extremely uncomfortable. Mogk et al. suggest that the patient’s family and doctor should approach Charles Bonnet Syndrome with empathy and a good sense of humor.