Visual release hallucinations, also known as Charles Bonnet syndrome or CBS, are a type of psychophysical visual disturbance in which a person with partial or severe blindness experiences visual hallucinations. First described by Charles Bonnet in 1760, the term Charles Bonnet syndrome was first introduced into English-speaking psychiatry in 1982. A related type of hallucination that also occurs with lack of visual input is the closed-eye hallucination. Signs and symptoms
People with significant vision loss may have vivid recurrent visual hallucinations (fictive visual percepts). One characteristic of these hallucinations is that they usually are "lilliputian" (hallucinations in which the characters or objects are smaller than normal). Depending on the content, visual hallucinations can be classified as either simple or complex. Simple visual hallucinations are commonly characterized by shapes, photopsias, and grid-like patterns. Complex visual hallucinations consist of highly detailed representations of people and objects. The most common hallucination is of faces or cartoons. Sufferers understand that the hallucinations are not real, and the hallucinations are only visual, that is, they do not occur in any other senses (such as hearing, smell or taste). Visual hallucinations generally appear when the eyes are open, fading once the visual gaze shifts. It is widely claimed that sensory deprivation is instrumental in the progression of CBS. During episodes of inactivity, hallucinations are more likely to occur.
Disrupting cortical homeostatic processes after vision has been lost may prevent or setback the emergence of hallucinations. At varying stages of the cortical grading, acetylcholine (ACh) may impact the balance of thalamic and intracortical inputs as well as the balance in between bottom-up and top-down. Particularly in CBS, a shortage of acetylcholine at cortical locations should correspond to the onset of hallucinations.The syndrome can also develop after bilateral optic nerve damage due to methyl alcohol poisoning. Diagnosis
A variety of disciplines including optometry, ophthalmology, geriatric medicine, psychiatry, and neurology play a part in securing the diagnosis of CBS. Since CBS is not commonly recognized by all clinicians, it oftentimes goes misdiagnosed and identified as psychosis, delirium, or dementia. As a result of this, it is estimated that almost 60% of CBS patients hesitate to notify their physicians. By focusing on the specific type of visual hallucination, one may find an accurate diagnosis. If a patient presents symptoms indicative of Charles Bonnet syndrome, basic laboratory examinations like metabolic panel and blood count tests, as well as neuroimaging, may aid in an accurate diagnosis. Prognosis
There is no treatment of proven effectiveness for CBS. For those experiencing CBS, knowing that they are suffering from this syndrome and not a mental illness seems to be the most comforting treatment so far, as it improves their ability to cope with the hallucinations.