Your grandmother has had macular degeneration for years and her vision is now quite limited. Lately, she’s mentioned seeing little people in the living room, especially in the evening. Does that mean that she now has dementia? Is she experiencing a mental illness or disconnect from reality?
Quite likely she is not! Hallucinations with severe vision loss are more common than you might expect, and there is a name for it: Charles Bonnet Syndrome. The condition is named after Charles Bonnet, a Swiss philosopher and writer who first described the condition in 1760 after witnessing his grandfather experience vision-loss hallucinations.
Charles Bonnet Syndrome (CBS) is a condition of temporary hallucinations in people with severe vision loss. The vision loss is usually due to one of the following three conditions:
- Macular degeneration
- Diabetic retinopathy
The visual hallucinations are typically quite simple—-seeing people, animals, houses, or other everyday objects. In some cases, more complex visions are animated or dreamlike and continue for a longer duration. These visual hallucinations are almost like a mirage, and often contain greater detail than what someone can detect in their actual surroundings.
CBS is sometimes referred to as “phantom vision syndrome” because it is similar to “phantom leg” syndrome. After an amputation, someone may continue to “feel” sensation in a limb that is no longer present. The feeling is created and experienced in the brain; there are no stimuli to create the sensation. Likewise, with CBS, the retinal cells in the eye are no longer receiving the visual images (due to damage from macular degeneration, glaucoma, or diabetic retinopathy). The brain begins creating its own “phantom” images using images stored in memory to create new “vision”.
The eye is only creating general images and cannot provide detail due to damage from the illness, yet the brain is still seeking those details. The brain will compensate for the weakness of the optic nerves and retina. Sometimes, the brain will do this by completing an image (i.e.: adding details that are not present); at other times, the brain may create whole images that are not present.
The hallucinations with Charles Bonnet Syndrome are visual illusions and are distinct from delusions. Visual illusions are a misinterpretation of external visual stimuli (interpreting the sweater on the couch for a cat, and adding the details of whiskers and eyes). Visual illusions affect only vision, none of the other senses. A delusion is believing something that is not true but believing it wholeheartedly (believing oneself to be the messiah). A delusion may include any of the senses and often a delusion is supported by more than one sense (hearing voices and seeing things for which there are no external stimuli).
Someone who is experiencing a visual illusion will accept that they have misinterpreted an image; someone who is delusional will not. Those with CBS are often quite aware that their perceived illusions are not real—they are able to rationalize that there cannot be miniature people standing in their living room. Some visions are surreal—small people, dragons, exotic animals—and other visions are realistic, such as seeing cows in a field.
CBS is most likely to affect someone soon after vision loss. The brain is still trying to interpret visual stimuli, even though the optic nerve and retina are no longer producing the images. Often, the brain will adapt to the loss of the incoming stimuli and the hallucinations will dissipate after 12-18 months, though some people have experienced CBS for many years.
CBS often goes undetected and undiagnosed. There is limited awareness of CBS—not just in the general public, but also in medical communities as well. Patients are often hesitant to report the symptoms of CBS because they fear being labelled “crazy” or mentally unstable.
Most estimates suggest 10-30% of those with severe vision loss will experience CBS; the most recent study conducted by the CNIB (Canadian National Institute for the Blind) surveyed 2500 people with low vision and found 18.8% had experienced hallucinations.
Of those who experienced hallucinations:
- Most common hallucinations were of people, animals, shapes or patterns
- Most people hallucinated daily—but for just a few seconds or minutes at a time
- 1/3 could get rid of hallucination by blinking
- 1/2 hallucinated in dim light, darkness, or while falling asleep
- 1/3 could not detect a pattern to their hallucinations
- 2/3 did not find their hallucinations to be bothersome
For many people, just knowing about CBS is a huge relief—it reassures them that they are not disconnected from reality and that there is a real phenomenon to explain their experiences. Unfortunately, there is no cure or treatment for CBS, and there isn’t one simple test to diagnose CBS. It is important that the doctor is alerted to hallucinations because it can be a symptom of other conditions, all of which should be ruled out before settling on a diagnosis of CBS.
While there is no cure for CBS, there are coping strategies such as:
- Closing your eyes or blinking rapidly
- Shifting eyes left to right every second for half a minute
- Adjusting lighting—some people need more light to reduce hallucinations; others find bright light causes hallucinations
- Watching TV or moving locations
- Explain to family and friends what you are experiencing