Visual hallucinations in psychosis are

hallucination A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinati ...

s accompanied by delusions.

Presentation

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 colorful or in black and white and can be static or have movement.

Simple vs. complex

Visual hallucinations may be simple, or non-formed visual hallucinations, or complex, or formed visual hallucinations. Simple visual hallucinations without structure are known as

phosphenes A phosphene is the phenomenon of seeing light without light entering the eye. The word ''phosphene'' comes from the Greek words ''phos'' (light) and ''phainein'' (to show). Phosphenes that are induced by movement or sound may be associated wit ...

and those with geometric structure are known as

photopsias Photopsia is the presence of perceived flashes of light in the field of vision. It is most commonly associated with: * posterior vitreous detachment * migraine aura (ocular migraine / retinal migraine) * migraine aura without headache * scinti ...

. These hallucinations are caused by irritation to the

primary visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

( Brodmann's area 17). 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.

Content

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 Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms become ...

, 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.

Causes

Two neurotransmitters are particularly important in visual hallucinations – serotonin and

acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Par ...

. They are concentrated in the visual thalamic nuclei and

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

. 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 Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...

, the interruption or destruction of the afferent connections of nerve cells, of the visual system, caused by

lesions A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classif ...

, leading to the removal of normal inhibitory processes on cortical input to visual association areas, leading to complex hallucinations as a release phenomenon.

Prevalence

The DSM-V lists visual hallucinations as a primary diagnostic criterion for several psychotic disorders, including schizophrenia and schizoaffective disorder. 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.

References

{{Reflist Hallucinations Medical signs Psychosis Symptoms and signs of mental disorders