When the eyes deceive – Charles Bonnet syndrome

Charles Bonnet syndrome (CBS) is not a visual condition itself, but rather a syndrome that is linked to visual impairment characterised by hallucinations.

People experiencing CBS see things that are not actually there. They may see people, animals or fantasy creatures, or geometric patterns such as lines or dots. For example, one client described seeing wolves sitting in the middle of the road. Another complained of constantly seeing a pink grid in her visual field. The experience of these hallucinations varies for people – some may see static images, some see moving ones, and some see the images in black and white while others see them in colour. The biggest difference between the hallucinations associated with CBS and those experienced by someone with mental illness is that the person with CBS knows they are hallucinating. The hallucinations are also purely visual (no strange voices accompany them).

Statistics report that one in five people with a visual impairment experiences the hallucinations of CBS. This number has been said to be as high as 50% in people with macular degeneration. Such statistics prove that it is an important syndrome for clients to know about. As the initial experience of these hallucinations can be scary, knowing that this is a common occurrence can bring comfort and support and give people the confidence to talk about it with their eye care specialist.

 

What causes CBS?

The cause of CBS is visual impairment itself, including even mild cases of visual impairment.

The occipital lobe, which receives visual information via the optic nerve, sends this neural (nerve) information to the brain, where it is decoded and transformed into images that make sense to us. When visual impairment is present, the visual areas of the brain stop receiving a stream of nerve activity. They are so used to being constantly stimulated and active that, when there is a sudden break in nerve activity, it is as if they don’t know what to do with themselves and try to fill in the gaps. To counteract the loss of stimulation, the visual brain areas start firing off nerve activity spontaneously and create the ‘made-up’ images experienced with CBS.

As different visual images are processed in different parts of the brain, the area of the brain that fires off spontaneously determines the type of hallucination a person sees.

 

It is common for CBS to be experienced in the first few weeks or months that follow a big change in vision as the brain adjusts to the change in incoming visual nerve activity. It is not yet clear why some people with visual impairments experience CBS and others do not.  

 

What are the symptoms of CBS?

Visual hallucinations are the key symptom a person with CBS will experience. They are normally very vivid images, which could last for a few minutes or even a few hours. People can experience them on and off for months or even years. The two distinct types of images experienced are simple pattens/shapes and complex images of objects, people or landscapes.

Some additional examples of CBS hallucinations include:

• Bright coloured patterns laid on top of the visual field, like a grid pattern
• Bright, clear shapes that intermix, like pink squares surrounded by yellow dots
• Patterns that look like tree branches spread across the visual field
• Distorted faces that appear in front of the person seeing them
• Waterfalls or a flowered garden that appear when looking at a kitchen
• Fantasy creatures like unicorns or elves when looking at a bedroom or bathroom
• People from different time periods, such as traditional Zulu warriors, appearing in view

 

How is CBS treated?

Diagnosis and treatment of CBS are not easy, as there are no real tests for diagnosing it, and not many treatment options.

To confirm its presence, the current protocol is for doctors to rule out any chance of the existence of any other mental illnesses that might be linked to the hallucinations. Some psychiatric tests might be involved. Other than that, if a person has vision loss and describes hallucination symptoms, it is generally considered a CBS diagnosis.

In recent years, doctors have tried prescribing medication used for other diseases, such as Alzheimer’s, Parkinson’s and epilepsy. Although using these has shown some positive results in helping people manage severely disturbing hallucinations, the medications are not prescribed as a standard treatment (a factor in this is their severe side-effects). Recent research has looked at the possibility of using electric current as another treatment option. However, further investigation is required before it is offered as a mainstream option.

For now, some of the best techniques used to ‘treat’ CBS hallucinations involve behavioural adaptations. Keeping the head still and moving the eyes left to right for 15-30 seconds is one option for people to try. Shutting the eyes and looking away from the hallucinated image or reaching for the image are other ways to try to interrupt the brain activity creating it. Changing activities or the lighting in a room might also help.

There still is much to learn about CBS. It is helpful for people to know that they are not alone in it and that the symptoms do not mean they have any kind of mental illness.

Written by Tracey Joubert, Orientation and Mobility Practitioner