Visual hallucination

Visual hallucinations in psychosis are reported to have physical properties similar to real perceptions. They are often life-sized, detailed, and solid, and are projected into the external world. They typically appear anchored in external space, just beyond the reach of individuals, or further away. They can have three-dimensional shapes, with depth and shadows, and distinct edges. They can be colorful or in black and white and can be static or have movement. == Conditions ==

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) identifies hallucinations as a critical diagnostic criterion for psychotic disorders, including schizophrenia and schizoaffective disorder. 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. In delirium, visual hallucinations are the most common type. 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. Simple vs. complex Visual hallucinations may be simple/non-formed visual hallucinations, or complex/formed visual hallucinations. Simple visual hallucinations without structure are known as phosphenes and those with geometric structure are known as photopsias. Sometimes, hallucinations are 'Lilliputian', i.e., patients experience visual hallucinations where there are miniature people, often undertaking unusual actions. Lilliputian hallucinations may be accompanied by wonder, rather than terror. Most people have multiple VH types. The content of hallucinations varies as well. Preliminary research has found that most individuals had multiple types of visual hallucinations. Scenes involving people and/or animals were the most common, followed by simple geometric images. Complex (formed) visual hallucinations are more common than Simple (non-formed) visual hallucinations. In contrast to hallucinations experienced in organic conditions, hallucinations experienced as symptoms of psychoses tend to be more frightening. An example of this would be hallucinations that have imagery of bugs, dogs, snakes, distorted faces. Visual hallucinations may also be present in those with Parkinson's, where visions of dead individuals can be present. In psychoses, this is relatively rare, although visions of God, angels, the devil, saints, and fairies are common. Individuals often report being surprised when hallucinations occur and are generally helpless to change or stop them. In general, individuals believe that visions are experienced only by themselves. ==Primary visual cortex==

V1's functional connection with other brain regions is reduced in psychotic patients who experience visual hallucinations. This contrasts with the expectation that V1 would be active during conscious visual perception. ==Causes==

Two neurotransmitters are particularly important in visual hallucinations – serotonin and acetylcholine. They are concentrated in the visual thalamic nuclei and visual cortex. The similarity of visual hallucinations that stem from diverse conditions suggest a common pathway for visual hallucinations. Three pathophysiologic mechanisms are thought to explain this. The first mechanism has to do with cortical centers responsible for visual processing. Irritation of visual association cortices (Brodmann's areas 18 and 19) cause complex visual hallucinations. 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. == Prevalence ==

Studies show that visual hallucinations are present in 16%–72% of patients with schizophrenia and schizoaffective disorder. Furthermore, visual hallucinations are reported in over 20% of individuals with dementia with Lewy bodies. ==See also==