Charles Bonnet Syndrome ( CBS for short) is defined as visual hallucinations occurring in patients with severe vision loss who have a normal cognitive function. This condition was first described in 1760 and affects about 30% of people with severe vision loss.
People experiencing CBS sees objects that they know are not real. Symptoms often start with seeing simple patterns and objects, such as bricks and fences. As the disease progresses, more complex hallucinations such as animals and even faces are seen.
Hallucinations may come and go and can last seconds to hours. Symptoms often are worse right after the vision loss and tend to subside within two years.
What’s going on? Let’s start by looking at the normal visual system. The eye captures images, conveys it to the part of the brain called the visual cortex, where the image is processed. This is how we perceive our world.
When a person has severe vision loss from diseases such as macular degeneration, the visual system is disrupted. The eye no longer captures images properly, but the other components of the visual pathway are healthy. The visual cortex, not having an image to process, starts to fill in the missing parts of the vision. The images that the visual cortex use to fill in the missing vision are images that the patient has seen before. These start with simple repeated patterns, then simple objects such as a fence or a brick wall. In advanced stages, animals and faces are often perceived.
Unlike patients with hallucinations from severe mental disorders, patients with CBS remember their hallucinations vividly. Awareness of their hallucinations makes people suffering from CBS frustrated and scared, thinking they have are crazy. It’s important to for doctors and family to talk to those with recent vision loss about these experiences. Reassure the patient that these hallucinations often improve and may resolve with time.
There is no reliable treatment for CBS. Because CBS is similar to another condition called phantom limb syndrome, some doctors may prescribe similar treatment for patients with severe CBS symptoms.