Charles Bonnet syndrome: definition, causes and symptoms.

Visual hallucinations caused by an impairment of visual and spatial perception.

Among the various perceptual systems, the visual system is the main tool through which our species perceives and reacts to its environment. Already from birth we possess a visual capacity that allows us to detect and react to the stimuli around us.

Sight, however, is an evolving sense, developing mainly during the first year of life. From a certain age, it is common for visual capacity to be reduced and problems such as eyestrain, cataracts and even glaucoma to appear.cataracts and even glaucoma. It is also possible that the areas of the brain responsible for vision may stop functioning with the usual precision, or that visual connections with other sensory and even intellectual processes may weaken.

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

What is Charles Bonnet Syndrome?

Charles Bonnet Syndrome is the clinical picture characterized by the appearance of visual hallucinations in patients with problems in the visual pathway, whether these problems are located in the visual organs, their connections to the brain or the brain 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 alterations, psychiatric, neurological or substance use disorders that could explain their appearance.

In other words, these hallucinations occur in healthy subjects with no other problem than visual hallucinations.The presence of dementia (a condition that sometimes also presents visual hallucinations), intoxications and other disorders must be ruled out.

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

Visual hallucinations

The hallucinations present in this type of disorder are very variable.The hallucinations present in this type of disorder are very variable, although they present a series of common characteristics such as occurring with clarity of consciousness, without any illusion of reality (i.e. the patient knows that it is not real), they are combined with normal perceptions, they appear and disappear without a clear cause and they are a phenomenon that surprises the sufferer, although there is not usually a great fear of them.

Regarding the content of the hallucinations that occur in Charles Bonnet Syndrome, the perception of human figures or animals of small size is frequent (type of hallucination called (type of hallucination called lilliputian), as well as of flashes or bright colors.

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

These hallucinations occur without a clear cause that triggers them.However, stress, excessive or poor lighting, or a lack or overload of sensory stimulation facilitate their appearance. The duration of the hallucinations is usually short, varying from seconds to hours, and they usually fade spontaneously when closing the eyes or redirecting the gaze towards them or towards another point.

Causes (etiology)

The causes of this syndrome, as already mentioned, are to be found in the loss of vision. This loss is usually caused by damage to the visual system, generally due to macular degenerations or glaucoma, and appears mainly in older subjects. However, it is also possible that this loss of vision is due to the presence of a brain pathology that hinders the connection between the eye and the occipital lobe.

But, even if an eye disease causes the loss of vision, the question arises as to why the hallucinations and Charles Bonnet Syndrome appear. In this sense, there is a wide diversity of theories that work on the subject, being one of the most accepted theories the Neuronal Deafferentiation Theory.

This theory is based on the consideration that due to the eye disease there is a loss of nerve impulses that should reach the occipital cortex, the area of the brain in charge of processing visual information. This causes the brain to become particularly sensitive to the stimuli that reach it, being affected by other stimuli as well.It is also affected by other sensory stimulations which, due to the hypersensitivity of the receptors, could lead to the perception of hallucinations, activating the visual area.

Treatment

Regarding the treatment of Charles Bonnet Syndrome, at a psychological level, the first thing to do is to reassure and provide information to the patient, who may be very anxious because he/she does not know what is happening and believes that he/she has some kind of dementia or mental disorder. It should be explained that the visions experienced are a consequence of the loss of vision.It would be advisable for ophthalmologists to report the possibility of the occurrence of this phenomenon as a consequence of vision loss in patients with diseases that degenerate this sense, encouraging patients to report their experiences.

At the pharmacological level, in general this type of disorder does not usually 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 in this syndrome is to treat the medical cause of the vision loss by increasing visual acuity as much as possible. It has been found that some patients with this syndrome have not returned to hallucinations after being operated on or treated for their visual problem.

Bibliographic references:

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