Charles Bonnet, His Life, and His Syndrome

doi:10.1016/j.survophthal.2006.10.007

Survey of Ophthalmology

Volume 52, Issue 1, January–February 2007, Pages 111-114

https://doi.org/10.1016/j.survophthal.2006.10.007 Get rights and content

Abstract

Charles Bonnet (1720–1792) was an eminent naturalist and philosopher whose contributions to botany and philosophy were highly regarded and honored by his contemporaries in the scientific community of his era in France and England. In1760 he first described and analyzed formed visual hallucinations experienced by his grandfather. The syndrome was named after Bonnet in 1937 by George de Mosier, another native of Geneva, Switzerland.

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Throughout the lifespan, the cerebral cortex adapts its structure and function in response to changing sensory input [1, 2]. Whilst such changes are typically adaptive, they can be maladaptive when they follow damage to the peripheral nervous system, including phantom limb pain and tinnitus [3, 4]. An intriguing example occurs in individuals with acquired ocular pathologies—most commonly age-related macular degeneration (MD) [5]—who lose their foveal vision but retain intact acuity in the peripheral visual field. Up to 40% of ocular pathology patients develop long-term hallucinations involving flashes of light, shapes, or geometric patterns and/or complex hallucinations, including faces, animals, or entire scenes, a condition known as Charles Bonnet Syndrome (CBS) [6, 7, 8]. Though CBS was first described over 250 years ago [9, 10], the neural basis for the hallucinations remains unclear, with no satisfactory explanation as to why some individuals develop hallucinations, while many do not. An influential but untested hypothesis for the visual hallucinations in CBS is that retinal deafferentation causes hyperexcitability in early visual cortex. To assess this, we investigated electrophysiological responses to peripheral visual field stimulation in MD patients with and without hallucinations and in matched controls without ocular pathology. Participants performed a concurrent attention task within intact portions of their peripheral visual field, while ignoring flickering checkerboards that drove periodic electrophysiological responses. CBS individuals showed strikingly elevated visual cortical responses to peripheral field stimulation compared with patients without hallucinations and controls, providing direct support for the hypothesis of visual cortical hyperexcitability in CBS.
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Visual hallucinations and illusions comprise some of the most vivid and sometimes bizarre symptoms in neuro-ophthalmology. Hallucinations are defined as perceptions that occur in the absence of a corresponding external sensory stimulus. Visual hallucinations can be classified as unformed/simple (e.g., dots, flashes, zig-zags) or formed/complex (actual objects or people). In contrast, illusions are misinterpretations of a true sensory stimulus. Visual hallucinations and illusions are generally positive phenomena, in contrast to visual loss, which is a negative phenomenon.
The causes of visual hallucinations and illusions can be grouped into several major categories: migraine, release phenomena (in the setting of impaired vision), entoptic (ocular) phenomena, alcohol and drug-related, seizures, neurogenerative disease, central nervous system lesions, psychiatric disease, and narcolepsy. This chapter details the various categories, but first the history, examination, and diagnostic and therapeutic considerations in patients with hallucinations and illusions are reviewed.
Bonnet, Charles
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Anton, balint, charles bonnet, and the others: The abc of cerebral visual syndromes (a historical guide and an update)
2024, Canadian Journal of Neurological Sciences

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: The author thanks Etienne Las Fargues, PhD, for the translations from the old French, and Thomas R. Hedges, III, MD, for assistance with the manuscript.

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History of OphthalmologyCharles Bonnet, His Life, and His Syndrome

Abstract

Surv Ophthalmol

Visual hallucinations as release phenomena

Albrecht Von Graefes Arch Klin Exp Ophthalmol

History of Ophthalmology
Charles Bonnet, His Life, and His Syndrome