Visual hallucinations are hallucinations of the visual modality. They can range from elementary flashes of light through fully formed visions of animals, objects and persons, to complex scenes.
Visual hallucinations characteristically occur in organic brain disturbances (delirium, occipital lobe tumors, epilepsy, dementia) and in the context of psychoactive substance use (lysergic acid diethylamide (LSD), mescaline, petrol/glue-sniffing, alcoholic hallucinosis [Details of these are described below]).
It is sometimes difficult to distinguish between internal images, illusions and clear visual hallucinations. An experience is described in Box X-1.
|A 69-year-old married man was referred to the duty psychiatrist in a casualty department for assessment. He said that his life was at an end and he deserved to die, as he had been caught masturbating by his daughter-in-law and grandchildren that afternoon. His wife said that this was not true; he had become very agitated and distressed over 12 hours and no one had visited the house that day. During interview, he was intensely agitated and put his hands in front of his face. He claimed that he could see clearly a sheet of glass half a meter in front of him, which he attempted to move. Later, he described seeing dust falling down everywhere and was trying to catch it. He manifested clouding of consciousness. A diagnosis of viral encephalitis was made on the basis of the history of persistent headache, the neurological signs and the finding of lymphocytosis in the cerebrospinal fluid.|
It is often difficult to decide whether the full criteria for the presence of a hallucination have been fulfilled in the visual modality. Distortion of visual percepts, based on either sensation of external stimuli or internal interference with the visual pathway, may produce disturbances that are similar to those occurring with entirely new perceptions.
Sometimes, the account of his experience given by the patient sounds like a sensory transformation rather than a hallucination, but the bizarre and complex nature of the experience renders phenomenological description difficult.
Visual hallucinations occur with occipital lobe tumors involving the visual cortex, for example tuberculous granuloma in the left occipital lobe caused a ‘starburst’ effect in the right visual field (Werring and Marsden, 1999).
Hallucinations Opens in new window and other visual disturbances may occur with other physical lesions, such as:
- loss of color vision, homonymous hemianopia (loss of half of the field of vision, the same half in both eyes; Komel, 1985),
- dyslexia (inability to read at a level appropriate to the individual’s age and intelligence) and alexia in a dominant hemisphere lesion, and cortical blindness (blindness due to a lesion of the cortical visual centre). They may, as in delirium tremens Opens in new window, be associated with an affect of terror or with an affect of hilarious absurdity.
Similar visual hallucinations, illusions Opens in new window and changes in mood occur in other forms of delirium Opens in new window. Visual hallucinations also occur in the post-concussional state, in epileptic twilight states and in metabolic disturbances, for example hepatic failure.
Visual hallucinations have also been described in association with various dementing processes, including:
- Alzheimer’s disease Opens in new window (Burns et al., 1990) ,
- senile dementia (Haddad and Benbow, 1992),
- multi-infarct dementia (Cummings et al., 1987),
- Pick’s disease Opens in new window (Ey, 1973) and
- Huntington’s chorea (Lishman, 1989).
Visual perceptual disturbances have also been observed in individuals after sniffing glue and petrol. The drugs mescaline and lysergic acid diethylamide are potent causes of visual perceptual change.
Visual hallucinations are infinitely variable in their content. They range from quite crudely formed flashes of light or color (elementary hallucinations), through more organized patterns and shapes, to complex, full, visual perceptions of people and scenes.
Visual and auditory hallucinations Opens in new window may occur synchronously in organic states, for example in temporal lobe epilepsy a visual hallucination of a human figure was also heard to speak.
Visual hallucinations are very uncommon in schizophrenia Opens in new window (although some of the earlier writers used the term hallucination for other visual abnormalities that occurred). Persaud and Cutting (1991) cautiously refer to ‘anomalous perceptual experiences in the visual modality’ in schizophrenic patients as, for example, the patient who although still recognizing a face considers it to be distorted.
These authors report four such cases of perceptual disturbance in one visual field, always the left field.
Visual hallucinations are not reckoned to occur in uncomplicated affective psychoses. It is common in schizophrenia for the patient to describe auditory hallucinations associated with visual pseudohallucinations Opens in new window.
Although the phonemes are complete and appear to have all the characteristics, subjectively, of a normal percept, the visual experiences are often inferred on the basis of the auditory hallucinations Opens in new window and of contemporaneous delusions Opens in new window.
It is possible to see, in most instances, how psychotically disordered fantasy accounts for the content of the visual experiences. Vivid elaborate scenic hallucinations have been described in oneiroid states of schizophrenia. In these states, there is also an altered state of consciousness.
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- Research data for this literature has been adapted from these following manuals:
- Sims' Symptoms in the Mind: An Introduction to Descriptive Psychopathology By Femi Oyebode
- Crash Course Psychiatry - E-Book By Katie FM Marwick, Steven Birrell
- Core Psychiatry E-Book, Edited by Padraig Wright, Julian Stern, Michael Phelan