Visual hallucinations due to Charles Bonnett Syndrome may be more common than you think
Are these cows real, or a visual hallucination?
According to an article in the August Edition of Review of Optometry, visual hallucinations experienced by people with poor vision may be due to Charles Bonnett Syndrome, or CBS. It occurs when visually impaired people experience complex visual hallucinations. These people are otherwise healthy, with normal mental ability and no evidence of psychiatric problems or brain abnormalities.
The syndrome is named after Swiss philosopher Charles Bonnett, who first recognized it.
Interestingly, even though people who experience CBS have poor vision, the hallucinations can be very vivid and detailed. Images can be quite distinct, allowing the person to identify different animal types or even faces. Strangely, the faces can be very clear, yet unfamiliar to the person experiencing the hallucination. Essentially they can see a very clear image of a stranger.
Research suggests 10% to 40% of visually impaired people can experience CBS, but this number is likely low. Many people don’t want to admit they experience hallucinations for fear of being labeled as suffering from dementia.
The exact reason for these hallucinations remains uncertain. One theory suggests nerves spontaneously generate images when they no longer receive stimulation from vision. Another theory claims the brain is responsible, attempting to “fill in” missing or distorted spots in the vision. While not entirely accurate, it helps to compare CBS to “phantom limb” syndrome, where a person who loses a limb from trauma sometimes states he can still feel the missing limb even though he knows it’s not there.
CBS is more common in elderly women, and the most common eye disease associated with the syndrome is age-related macular degeneration. Other conditions that may cause CBS include cataracts, glaucoma, retinitis pigmentosa, retinal detachments, and diabetic retinopathy.
My own patients have admitted to hallucinations including images of people, animals (cows and elephants), and trees. Sometimes they only realize the images are hallucinations when someone with them reveals it. For example, I had one patient look out her window and say to a friend, “Look how those cows have gathered in that field.” Her friend pointed out that the field was empty. Other times patients realize they are hallucinating, like the patient who told me she saw a beautiful grove of trees in the middle of the highway.
Unfortunately, not much can be done for people experiencing visual hallucinations. The good news is the frequency of the hallucinations tends to decrease with time. This can be comforting to someone suffering from CBS. Also, the best treatment may be to maximize remaining vision and decrease glare. A low vision specialist may be helpful in many cases.
Another good idea is to realize that Charles Bonnett Syndrome exists at all. If you work with or have family or friends suffering from impaired vision, it can be helpful to simply ask if they have experienced visual hallucinations. It may be the first step to getting them the help they need.
