Abstract and Introduction
Introduction
A visual hallucination is a visual percept experienced when awake that is not elicited by an external stimulus. Historically, hallucinations have been synonymous with psychiatric disease, most notably schizophrenia; however, over recent decades, hallucinations have been categorized based on their underlying etiology as psychodynamic (primary psychiatric), psychophysiologic (primary neurologic/structural), and psychobiochemical (neurotransmitter dysfunction).[1] Presently, visual hallucinations are known to be caused by a wide variety of primary psychiatric, neurologic, ophthalmologic, and chemically-mediated conditions. Despite these causes, clinically differentiating the characteristics and qualities of visual hallucinations is often a lesser-known skillset among clinicians. The utility of this skillset is important for the clinician's ability to differentiate the expected and unexpected characteristics of visual hallucinations in patients with both known and unknown neuropsychiatric conditions.
Though many primary psychiatric and neurologic conditions have been associated with and/or known to cause visual hallucinations, this review focuses on the following grouped causes:
Primary psychiatric causes: psychiatric disorders with psychotic features and delirium; and
Primary neurologic causes: neurodegenerative disease/dementias, seizure disorders, migraine disorders, vision loss, peduncular hallucinosis, and hypnagogic/hypnopompic phenomena.
Because the accepted definition of visual hallucinations excludes visual percepts elicited by external stimuli, drug-induced hallucinations would not qualify for either of these categories. Additionally, most studies reporting on the effects of drug-induced hallucinations did not control for underlying comorbid psychiatric conditions, dementia, or delirium, and thus the results cannot be attributed to the drug alone, nor is it possible to identify reliable trends in the properties of the hallucinations.[2] The goals of this review are to characterize visual hallucinations experienced as a result of primary psychiatric and primary neurologic conditions and describe key grouping and differentiating features to help guide the diagnosis.
Curr Psychiatr. 2023;22(3):15-24. © 2023 Current Psychiatry
