Charles Bonnet syndrome (CBS) is an under-recognised condition affecting people who have lost vision due to various eye conditions such as Age-Related Macular Degeneration (AMD), glaucoma, and diabetic retinopathy.

CBS was first described in 1760 by Charles Bonnet (1720‐1792), an eminent naturalist and philosopher who described the visual hallucination suffered by his grandfather. It was named in 1937 by George de Moasier who, like Charles Bonnet, was a native of Geneva, Switzerland. CBS is characterised by vivid, elaborate and recurrent visual hallucinations in psychologically normal people.

It most often occurs in older, visually impaired persons. AMD has been reported as a leading cause. The prevalence of Charles Bonnet Syndrome varies and ranges from 0.4% to 30%, depending on the study.3 The wide variability in prevalence is due to several reasons. There is no universally accepted definition of CBS, the diagnosis of CBS is made across different disciplines and many people are hesitant to report that they experience visual hallucinations.

The incidence of CBS is higher in subjects with worse visual acuity. Worse vision is associated with an increased risk of experiencing visual hallucinations. Complex hallucinations tend to occur in people with lower acuity, more extensive field loss and poor social contact. Some authors have suggested there may be an increased risk of CBS symptoms in those with declining cognitive function. However, this remains controversial, and other studies have suggested this is not the case and that a requirement for the diagnosis of CBS is normal neuropsychological function.

CBS may occur due to a significant ocular disorder such as AMD, or cortical causes such as damage of the sensory nerve fibres in the cerebral cortex, the outer layer of the cerebrum in the brain. A simple explanation is that the visual hallucinations experienced by some people with vision loss are like the phantom limb sensations that may occur
after amputation – the brain is active and is filling in vision gaps caused by the underlying disorder.

CBS hallucinations can range from simple shapes and dots of colours to detailed pictures of people, animals, landscapes or buildings. The images usually last for a few minutes, but in some cases, a few hours. CBS only affects vision and none of the other senses, i.e. hearing, smelling, touch and taste. CBS hallucinations occur in a clear state
of consciousness when the patient is alert and awake.
© Copyright 2014 – The Royal Australian and New Zealand College of Ophthalmologists.

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