Table 1

Visual hallucinations in wider clinical and non-clinical context

ConditionKey features
Parkinson’s diseaseOccurs throughout PD from early stage disease without cognitive impairment to PDD (see above). Other hallucination modalities can be involved in later stages.
Charles Bonnet syndromeEye or visual pathway disease (see above).
DementiaIncludes AD, DLB, PDD, AD, VaD (see above). Other hallucination modalities can be involved.
Comorbid diseaseEye and neurodegenerative disease combined (see above).
Schizophrenia/bipolar disorderVisual hallucinations are less prevalent than auditory hallucinations in schizophrenia and other psychoses. VH in these conditions rarely occur without auditory hallucinations during the course of the illness and are typically interspersed with unimodal auditory hallucinations.
BereavementVH of the deceased can occur as part of normal grief reaction but are less frequent than sensed presence of the deceased.
DeliriumVH are the most common modality of hallucination in delirium where they occur in the context of clouded consciousness, sleep dysregulation and affective symptoms.
Sleep-relatedOccasional VH can be normal experiences at the margins of sleep (hypnagogic/hypnopompic hallucinations). They may also present as part of a sleep-disorder (eg, narcolepsy).
Medication side effectsPD medication can precipitate VH but the exact mechanism and its relation to PD neurodegeneration is unclear. Medication with anti-muscarinic effects and opiates are particularly implicated in VH.
Hallucinogen useVisual perceptual phenomena including visual snow (see below) afterimages, palinopsia and flashback VH may persist after hallucinogen exposure (hallucinogen persisting perception disorder).
Peduncular hallucinationsComplex visual hallucinations caused by brainstem or thalamic lesions. When caused by brainstem lesions, VH are associated with sleep disturbance and eye movement dysfunction. Hallucinations in other modalities can occur.
Occipital/temporal seizuresIctal phenomenology is based on location of seizure. Simple VH are associated with occipital foci. Complex VH imply involvement of the temporal lobe and limbic cortex.
MigraineTeichopsia in classical migraine aura and other visual perceptual phenomena.
Visual snow syndromeA syndrome characterised by persistent dynamic visual noise (snow), palinopsia, entopic phenomena, photophobia and nyctalopia. Associated with migraine.
  • AD, Alzheimer’s disease; DLB, dementia with Lewy bodies; PD, Parkinson’s disease; PDD, Parkinson’s disease dementia; VaD, vascular dementia; VH, visual hallucinations.