Primer on Charles Bonnet Syndrome

Charles Bonnet (pronounced “bon-nay”) was a naturalist and philosopher born in Geneva in 1720. At around 40 years-old, he released a book called “Essai Analytique sur les Faculties de L’Ame” (Analytical Essays Concerning the Faculties of the Mind) in which he described how his 87 year-old grandfather, Charles Lullin, experienced visual hallucinations that occurred at spontaneous times. 

Fast forward to 1967, the term “Charles Bonnet Syndrome (CBS)” was introduced to the world by another Geneva native, George de Morsier.

CBS can be described as the presence of visual hallucinations among those with sight loss. These hallucinations are completely the product of visual impairments and are not signs of mental health deterioration. 

There are generally two main types of hallucinations experienced:

  • Simple patterns and shapes, like brickwork or mosaic
  • Complex images of people, landscapes, or objects

These will only affect a person’s sight. Smell, hearing, and touch will not be compromised. 

The reasons behind these hallucinations are not yet entirely clear. It is suggested that when sight loss occurs, the brain no longer receives as many signals from the eyes. It then attempts to make up for this lack of communication by creating its own. These end up translating into “phantom” images seen by the individual. 

CBS normally appears in the weeks and months following a big change in sight loss. Fortunately, for the majority of people, these hallucinations get less frequent with time, although reappearance of hallucinations five years after initially starting is a possibility. 

One of the most serious aspects of CBS is its unknown nature. Many people who begin experiencing hallucinations are often unaware of its true nature. This can cause fear for both the individual as well as their family and friends, due to visions being taken to be symptoms of mental health issues. 

Unfortunately, there is no direct way to diagnose the presence of CBS. Doctors will generally talk to the patient about their medical history and may carry out tests to rule out other causes for the visual hallucinations. 

Although no treatment is available, given enough time, CBS can improve over time. It has been found that often simply a better understanding of CBS can help patients cope better as they understand that it is purely a normal result of sight loss rather than anything to do with mental health. In some cases, medication for epilepsy, Parkinson’s Disease, and dementia have been able to help, but due to the possibility of severe side-effects, it is only recommended for those who are seriously affected and under supervision. 

There are, however, a few self-help methods that may relieve any hallucinations experienced:

  • Changing lighting conditions, i.e. making it brighter or dimmer
  • Scanning from left to right repeatedly without moving the head for 15 secs. This can be done 4 or 5 times if hallucination continues.
  • Staring at an image and blinking rapidly, or attempting to touch it. 
  • Performing a task that includes large movement, e.g. going to the kitchen to make coffee
  • Sleeping and resting well. Fatigue and stress may increase the likelihood of hallucinations.