Charles Bonnet syndrome

Charles Bonnet syndrome (CBS) occurs in patients with loss of vision (usually due to ocular pathology) who experience visual hallucinations. 

Epidemiology

Although numerous causes are seen (any cause of gradual ocular visual failure can theoretically produce Charles Bonnet syndrome, as can other locations for visual loss, e.g. optic chiasm, optic radiation, and occipital lobes), the most common is macular degeneration ¹; representing how prevalent this condition is. Therefore, not surprisingly, elderly patients are most commonly affected ¹.

Clinical presentation

Patients typically experience hallucinations when awake with eyes open, typically in the evenings or at night ¹. The hallucinations themselves are not stereotyped (i.e. they vary from day to day), and patients have insight into the fact that these are not real, and tend not to be distressed by them ¹.

Radiographic features

Imaging of the brain is two-fold:

• in patients with ocular pathology, to exclude other causes of visual hallucinations (e.g. peduncular hallucinosis, Lewy body dementia)
• in those without ocular pathology, a lesion along the optic tracts-occipital cortex should be sought

History and etymology

Charles Bonnet syndrome is named after Charles Bonnet, pronounced "bon-nay", (1720-1792) a Swiss-born French biologist who made important contributions to entomology and botany. He was also the first individual to use evolution in the biological sense. In 1760 he published an essay in which he described distinctive visual hallucinations as related to him by his grandfather. It was not until in 1967 that George de Mosier, another renowned Swiss scientist, named the syndrome after his famous compatriot ⁴.