Visual hallucinations: Differentiating psychiatric and neurologic causes

Content and perceived physical properties. Hallucinated entities are most often perceived as solid, 3-dimensional, well-detailed, life-sized people, animals, and objects (often fire) or events existing in the real world.³ The entity is almost always perceived as real, with accurate form and color, fine edges, and shadow; is often out of reach of the perceiver; and can be stationary or moving within the physical properties of the external environment.³

Timing and triggers. The temporal properties vary widely. Hallucinations can last from seconds to minutes and occur at any time of day, though by definition, they must occur while the individual is awake.³ Visual hallucinations in psychosis are more common during times of acute stress, strong emotions, and tiredness.³

Patient reaction and belief. Because of realistic qualities of the visual hallucination and the perception that it is real, patients commonly attempt to participate in some activity in relation to the hallucination, such as moving away from or attempting to interact with it.³ Additionally, patients usually perceive the hallucinated entity as uncontrollable, and are surprised when the entity appears or disappears. Though the content of the hallucination is usually impersonal, the meaning the patient attributes to the presence of the hallucinated entity is usually perceived as very personal and often requiring action. The hallucination may represent a harbinger, sign, or omen, and is often interpreted religiously or spiritually and accompanied by comorbid delusions.³

Visual hallucinations of delirium

Delirium is a syndrome of altered mentation—most notably consciousness, attention, and orientation—that occurs as a result of ≥1 metabolic, infectious, drug-induced, or other medical conditions and often manifests as an acute secondary psychotic illness.¹² Multiple patient and environmental characteristics have been identified as risk factors for developing delirium, including multiple and/or severe medical illnesses, preexisting dementia, depression, advanced age, polypharmacy, having an indwelling urinary catheter, impaired sight or hearing, and low albumin levels.^13-15 The development of delirium is significantly and positively associated with regular alcohol use, benzodiazepine withdrawal, and angiotensin receptor blocker and dopamine receptor agonist usage.¹⁵ Approximately 40% of patients with delirium have symptoms of psychosis, and in contrast to the hallucinations experienced by patients with schizophrenia, visual hallucinations are the most common type of hallucinations seen in delirium (27%).¹³ In a 2021 review that included 602 patients with delirium, Tachibana et al¹⁵ found that approximately 26% experienced hallucinations, 92% of which were visual hallucinations.

Content, perceived physical properties, and reaction. Because of the limited attention and cognitive function of patients with delirium, less is known about the content of their visual hallucinations. However, much like those with primary psychotic symptoms, patients with delirium often report seeing complex, normal-sized, concrete entities, most commonly people. Tachibana et al¹⁵ found that the hallucinated person is more often a stranger than a familiar person, but (rarely) may be an ethereal being such as a devil or ghost. The next most common visually hallucinated entities were creatures, most frequently insects and animals. Other common hallucinations were visions of events or objects, such as fires, falling ceilings, or water. Similar to those with primary psychotic illness such as schizophrenia, patients with delirium often experience emotional distress, anxiety, fear, and confusion in response to the hallucinated person, object, and/or event.¹⁵

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