Charles Bonnet Syndrome

After watching Oliver Sacks’ TED talk, “What Hallucination Reveals About Our Minds”, I was intrigued by a dementia patient who was experiencing hallucinations after going blind through macular degeneration. Sacks had concluded that she was suffering from Charles Bonnet Syndrome, or also called Visual Release Hallucinations. This post aims to give an outline of the syndrome, and explore treatments and causes.

Charles Bonnet Syndrome (CBS) is characterised as a type of psychophysical visual disturbance and sufferers are blind or severely visually impaired and experience intricate visual hallucinations. A characteristic of these hallucinations is the that they appear “lilliputian”, i.e. they are smaller than usual. Cartoons are typical hallucinations, as Sacks’ patient commonly experienced. The significant part of CBS is that the sufferer’s are aware that the hallucinations are not real.

The prevalence of CBS was explored in an Australian Study which found that amongst adults over 65, 17.5% experienced these hallucinations. However the incidence may be higher as sufferer’s may be fearful of reporting the hallucinations for fear of being labelled mentally ill.

The syndrome can be developed after damage to the bilateral optic nerve occurs through methyl alcohol poisoning. Macular degeneration combined with restriction of the visual field after glaucoma can also predispose CBS. Diabetes-related eye conditions and cataracts can also lead to visual hallucinations. The hallucinations experienced in CBS can be heightened through intense emotional distress such as grief, or depression, sensory deprivation, strokes and impaired cognitive abilities.

The hallucinations occur as a result of the brain reacting to losing sight, the brain reacts to visual loss by producing images that had previously been seen, as it is no longer receiving any visual input.

There are not express treatments for CBS, however it has been observed that after the patients are aware that the hallucinations are not part of a mental disorder, but a reaction to loss of sight, the hallucinations become less frequent. It is believed that no treatment is required due to the fact that the hallucinations are believed not to be permanent and will eventually fade away on their own.

However, it has been found that drugs used to treat Parkinson’s, dementia and epilepsy have been found to alleviate the hallucinations- but it must be known that these medications have side-effects, and it is also possible that these medications intensify the hallucinations.


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