Charles Bonnet syndrome: definition, causes and symptoms

Among the various perceptual systems, the visual system is the main tool by which our species perceives and reacts to its environment. From birth, we have a visual capacity that allows us to detect and respond to stimuli around us.

Sight, however, is an evolving sense, developing primarily during the first year of life. From a certain age, the visual impairment is often reduced and problems such as tired eyesight appear., Cataracts and even glaucoma. It is also possible that the areas of the brain in charge of vision cease to function with the usual precision, or that the visual connections with those of other sensory and even intellectual processes are weakened.

This type of problem can cause our visual system to perceive stimuli that are not present, as in the case of Charles Bonnet syndrome.

What is Charles Bonnet syndrome?

By Charles Bonnet syndrome is meant the clinical picture characterized by the appearance of visual hallucinations in patients with visual problems, whether these problems are localized in the visual organs, their connections with the brain or the areas involved in vision.

The main diagnostic criteria for this syndrome are the aforementioned presence of visual hallucinations and that these occur in the total absence of cognitive and consciousness disorders, psychiatric, neurological or drug addiction disorders which could explain their appearance.

In other words, these hallucinations occur in healthy subjects without any problem other than the visual itself, Duty to exclude the presence of dementia (an image that sometimes also has visual hallucinations), poisoning and other disorders.

Thus, Charles Bonnet syndrome appears mainly in healthy individuals who do not suffer from any alteration other than vision loss. Since a large proportion of visual problems appear during old age, it is particularly prevalent in the elderly population.

visual hallucinations

The hallucinations present in this type of disorder are very variable, Although they have a number of common characteristics such as occurring with a clear awareness, without presenting an illusion of reality (i.e. the patient knows that it is something unreal), they are combined with perceptions. Normal, appear and disappear without a clear cause for it and is a surprising phenomenon that affects them, although there is usually no great fear about them.

As for the content of the hallucinations that occur in Charles Bonnet syndrome, the perception of small human or animal figures is frequent (A type of hallucination called Lilliputian), as well as flashes or bright colors.

The perception itself is clear and vivid, located in the space outside the person (i.e. false perceptions are perceived as elements of the environment, although they are recognized as unreal) , with a high level of definition that contrasts sharply with real perception (remember that this syndrome occurs in people with visual loss, who therefore see more blurred real stimuli).

These hallucinations occur without a clear cause that triggers them; although stress, excessive or poor lighting, or lack or overload of sensory stimulation facilitate its onset. The duration of hallucinations is usually short and can vary from a few seconds to a few hours, and usually subsides spontaneously when you close your eyes or redirect your gaze to them or to another point.

Causes (etiology)

The causes of this syndrome, as already mentioned, are found in the loss of vision. This loss is usually caused by damage to the visual system, being mainly macular degeneration or glaucoma and occurring mainly in the elderly. However, it is also possible that this loss of vision is due to the presence of a brain pathology that makes it difficult to connect the eye to the occipital lobe.

But even if eye disease causes vision loss, one has to wonder why hallucinations and Charles Bonnet syndrome arose. In this sense, there is a great diversity of theories that work on the subject, one of the most accepted being the Neuronal dissociation theory.

This theory is based on the consideration that due to eye disease, there is a loss of nerve impulse that should reach the occipital cortex, the area of ​​the brain responsible for processing visual information. This makes the brain particularly sensitive to stimuli that reach it, Being additionally affected by other sensory stimuli which before receptor hypersensitivity could form the perception of hallucinations, activating the visual area.


Regarding the treatment of Charles Bonnet syndrome, on a psychological level, the first thing to do is to reassure and inform the patient, who may present with great anxiety not knowing what is going on and believing that ‘he has a form of dementia. or a mental disorder. Explain that the visions you experience are a consequence of vision lossIt is recommended that ophthalmologists report the possibility of this phenomenon as a result of vision loss in patients with diseases that degenerate this sense, encouraging patients to share their experiences.

Pharmacologically, in general, this type of disorder does not generally respond positively to neuroleptics, although in some cases haloperidol and risperidone have shown some efficacy. Anticonvulsants such as carbamazapine have also been proposed.

However, the most useful thing in this syndrome is to treat the medical cause that is causing the vision loss, increasing visual acuity as much as possible. It has been found that some patients with this syndrome no longer had hallucinations after being operated on or treated for their visual problem.

Bibliographical references:

  • Belloch, A., Bains, R. and Perpiñá, C. (2008) Psychopathology of perception and imagination. In A. Belloch, B. Sandín and F. Ramos (Eds.) Handbook of Psychopathology (2nd edition). Vol I, Madrid: McGraw Hill Interamericana.
  • Burke, W. (2002). The neural basis of Charles Bonnet’s hallucinations: a hypothesis. J Neurol neurosurgery Psychiatry; 73: 535-541
  • Morsier, G. (1936) Pathogenesis of peduncular hallucinations. About a new case. Schweizerische Medizinische Wochenschrift; 27: 645-646.
  • Luque, R. (2007). Hallucinations: historical and clinical review. Psychiatric Information, nº189.
  • Podoll, K .; Osterheider, M. and Noth, J. (1989). Charles Bonnet syndrome. Advances in neurology and psychiatry; 57: 43-60.
  • Santhouse, AM; Howard, RJ and Ffytche, DH (2000). Visual hallucinatory syndromes and visual anatomy of the brain. Brain; 123: 2055-2064.
  • Lapid, MI; Burton. MC; Chang, MT et al. (2013) Clinical phenomenology and mortality in Charles Bonnet syndrome. J Geriatr Psychiatry Neurol; 26 (1): 3-9.
  • Tan, CS; Yong, VK and Au Eong, KG (2004) Appearance of Charles Bonnet syndrome (visual hallucinations formed) after bilateral peripheral laser iridotomies. Eye; 18: 647-649.
  • Yacoub, R. and Ferruci, S. (2011). Charles Bonnet syndrome. Optometry; 82: 421-427.

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