Visual hallucinations in psychosis are hallucinations accompanied by delusions, which are abnormal beliefs that are endorsed by patients as real, that persist in spite of evidence to the contrary, and that are not part of a patient’s culture or subculture.
Visual hallucinations in psychoses 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 colourful or in black and white and can be static or have movement.
Simple versus Complex
Visual hallucinations may be simple, or non-formed visual hallucinations, or complex, or formed visual hallucinations.
Simple visual hallucinations are also referred to as non-formed or elementary visual hallucinations. They can take the form of multicoloured lights, colours, geometric shapes, indiscrete objects. Simple visual hallucinations without structure are known as phosphenes and those with geometric structure are known as photopsias. These hallucinations are caused by irritation to the primary visual cortex (Brodmann’s area 17).
Complex visual hallucinations are also referred to as formed visual hallucinations. They tend to be clear, lifelike images or scenes, such as faces of animals or people. 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.
The frequency of hallucinations varies widely from rare to frequent, as does duration (seconds to minutes). The content of hallucinations varies as well. 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.
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 centres 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.
The third mechanism has to do with the reticular activating system, which plays a role in the maintenance of arousal. Lesions in the brain stem can cause visual hallucinations. Visual hallucinations are frequent in those with certain sleep disorders, occurring more often when drowsy. This suggests that the reticular activating system plays a part in visual hallucinations, although the precise mechanism has still not fully been established.
Hallucinations in those with psychoses are often experienced in colour, and most often are multi-modal, consisting of visual and auditory components. They frequently accompany paranoia or other thought disorders, and tend to occur during the daytime and are associated with episodes of excess excitability. The DSM-V lists visual hallucinations as a primary diagnostic criterion for several psychotic disorders, including schizophrenia and schizoaffective disorder.
The lifetime prevalence of all psychotic disorders is 3.48% and that of the different diagnostic groups are as follows:
- 0.87% for schizophrenia.
- 0.32% for schizoaffective disorder.
- 0.07% for schizophreniform disorder.
- 0.18% for delusional disorder.
- 0.24% for bipolar I disorder.
- 0.35% for major depressive disorder with psychotic features.
- 0.42% for substance-induced psychotic disorders.
- 0.21% for psychotic disorders due to a general medical condition.
Visual hallucinations can occur as a symptom of the above psychotic disorders in 24% to 72% of patients at some point in the course of their illness. Not all individuals who experience hallucinations have a psychotic disorder. Many physical and psychiatric disorders can manifest with hallucinations, and some individuals may have more than one disorder that could cause different types of hallucinations.