These experiences are involuntary and possess a degree of perceived reality sufficient to resemble authentic visual perception.
[2][3] Visual hallucinations are not restricted to the transitional states of awakening or falling asleep and are a hallmark of various neurological and psychiatric conditions.
[3] They are documented in schizophrenia, toxic encephalopathies, migraines, substance withdrawal syndromes, focal central nervous system lesions, and psychotic mood disorders.
[3] Although traditionally linked with organic aetiologies, visual hallucinations occur in approximately 25% to 50% of individuals with schizophrenia.
[1] Despite their prevalence, the underlying mechanisms remain poorly understood, which hinders the development of targeted therapeutic approaches.
Conditions causing complex visual hallucinations include schizophrenia, Charles Bonnet syndrome, migraine coma, treated idiopathic Parkinson's disease, epilepsy, narcolepsy-cataplexy syndrome, Lewy body dementia without treatment, peduncular hallucinosis, and hallucinogen-induced states.
[13] Stimulant intoxication (e.g., cocaine or methamphetamine) is frequently accompanied by visual hallucinations, which may involve perceptions of crawling insects due to associated tactile disturbances.
[citation needed] The frequency of hallucinations varies widely from rare to frequent, as does duration (seconds to minutes).
[7][8] V1's functional connection with other brain regions is reduced in psychotic patients who experience visual hallucinations.
[17][21] The second mechanism is deafferentation, the interruption or destruction of the afferent connections of nerve cells, of the visual system, caused by lesions, leading to the removal of normal inhibitory processes on cortical input to visual association areas, leading to complex hallucinations as a release phenomenon.
[19][21] Studies show that visual hallucinations are present in 16%–72% of patients with schizophrenia and schizoaffective disorder.