Different Types of Visual Hallucination
Visual hallucinations are defined as perceptions of an object or occurrence in the absence of physical stimuli. The differential diagnosis for this phenomenon is broad and encompasses ophthalmic, neurologic, metabolic and psychiatric etiologies. In order to discern the underlying cause of a visual hallucination, a thorough patient history in conjunction with various metabolic and imaging studies may be utilized to rule out pathologic etiologies. Here, the differential diagnoses for visual hallucinations are discussed.
The most common patient demographic that experiences visual hallucinations is highly variable and contingent upon the cause for the hallucination. For patients experiencing visual hallucination secondary to primary psychosis, the most common demographic would be dictated by the epidemiology of the psychiatric disease. For instance, schizophrenia is typically diagnosed in the later teens to early thirties and more frequently affects men. For patients experiencing hallucinations secondary to delirium, hospitalized patients and patients who suffer from substance withdrawals are the most common demographic. Visual hallucinations related to migraines are more common in women as migraines are more common among this population; additional information may be found here: Ophthalmologic Manifestations of Migraines. Visual hallucinations secondary to seizures can occur in any age group depending on the etiology of the seizure (i.e. intracranial hemorrhage, stroke, infection, etc.) Additional information regarding the most common demographic experiencing visual hallucinations secondary to seizures may be found here: Ophthalmologic Manifestations of Epilepsy. Visual hallucinations occurring secondary to sleep deprivation may occur in patients of any age or gender experiencing insomnia. Visual hallucinations due to drug effects more commonly occur among young adults who use recreational substances or older adults taking prescription medication with neuroactive side effects. Patients experiencing visual hallucinations secondary to a brain tumor range widely in age and demographic; therefore, the most common patient population is dictated by tumor type and location. Visual hallucinations secondary to optic nerve damage more commonly occurs affects a varied group of patients depending on the etiology of the optic nerve damage (i.e. papilledema, infectious optic neuritis, etc.) Charles Bonnet syndrome is a type of visual hallucination more commonly seen in elderly patients as this syndrome is detected in patients with minimal visual acuity due to severe ophthalmic disease. Peduncular Hallucinosis, Alice in Wonderland Syndrome, and Anton-Babinski syndrome are all causes of visual hallucination with a highly variable patient demographic. Palinopsia is a visual hallucination thought to be related to etiologies such as brain tumors and substance use, so the most common demographic affected is related to the etiologies of those underlying causes.
The pathogenesis of visual hallucination is dependent on its etiology and has complex mechanisms. The hallucinations secondary to primary psychosis and delirium are likely due to increased dopaminergic transmission and neurotransmitter imbalances within the subcortical regions of the brain. Visual hallucinations secondary to migraines are related to stimulation of the occipital cortex, and further information regarding their pathogenesis can be found here: Ophthalmologic Manifestations of Migraines. The pathogenesis of visual hallucinations secondary to seizures can be found here: Ophthalmologic Manifestations of Epilepsy. The etiology of visual snow arises from hypersensitivity to visual stimuli; more information is found here: Visual Snow. Visual symptoms arising from dementia-inducing pathologies, such as Parkinson’s and Alzheimer’s, arise from disease involvement of the visual cortex; more information can be found here: Visual Symptoms of Parkinson’s Disease, Visual Variant of Alzheimer’s Disease. Prolonged sleep disturbances may induce hallucinations similar to the clinical picture of psychosis, and their pathogenesis is thought to be linked to dysfunction of the reticular activating system. Drug usage and withdrawal may precipitate visual hallucinations due the stimulation of 5-HT(2A) on neocortical pyramidal cells. Furthermore, certain drugs may precipitate a lasting hallucination known as hallucinogen persisting perception disorder; more information on this disorder may be found here: Hallucinogen Persisting Perception Disorder. Tumors may induce visual hallucinations if they compress the optic tract or affect the posterior visual cortex due to disruption in transmission in visual information. Optic nerve damage secondary to a variety of etiologies, such as papilledema and optic neuritis, is thought to cause visual phenomena due a disruption in the integrity of the retinal nerve fibers. The pathogenesis of Charles Bonnet Syndrome can be found here: Charles Bonnet Syndrome. The pathogenesis of Peduncular Hallucinosis can be found here: Peduncular Hallucinosis. The pathogenesis of Alice in Wonderland Syndrome can be found here: Alice in Wonderland Syndrome. The pathogenesis of Anton-Babinski Syndrome can be found here: Anton Syndrome. The pathogenesis of palinopsia can be found here: Palinopsia.
Physical Examination and Diagnostics
Clinical findings and testing recommendations for a patient experiencing visual hallucinations is variable and dependent on the underlying pathology. In order to discern the underlying etiology of visual hallucination, a thorough ophthalmologic workup consisting of dilated fundus exam (DFE), Humphrey visual field testing, and OCT macula/RNFL testing is recommended to rule out ophthalmic pathology. Neurologic etiologies should be explored through a thorough neurologic examination, brain imaging (including CT and MRI), EEG studies, and/or sleep studies. Metabolic causes may be excluded through a metabolic work up consisting of BMP, CBC, and LFTs. If a psychiatric cause is suspected, a psychiatric evaluation is recommended for appropriate diagnosis and management. Certain pathologies, such as psychiatric disease, seizures, and delirium, do not always require ophthalmologic work-up and instead likely warrant medical management. Imaging, such as MRI and CT, and metabolic analyses should be performed to rule out any co-existing cause of visual hallucination. Tumors may produce repeatable visual field deficits on visual field testing depending on its location along the visual pathway. Further brain imaging (MRI) should be performed for additional information on the size and location of the lesion. Optic nerve damage has a wide range of ophthalmologic presentations on examination depending on the cause for damage, and may be assessed with a thorough dilated examination, OCT RNFL, and visual field testing.
Symptoms of visual hallucinations due to psychiatric disease, neurologic pathology, or substance use are highly variable, even among patients experiencing visual phenomena due to identical underlying etiologies. Hallucinations may involve simple images, such as the perception of flashing lights or squiggling lines, to complex and complete images, such as animals, religious figures or family members. Certain etiologies of visual hallucination, such as migraine-induced hallucinations, have a characteristic presentation. In the aforementioned example, the classic presentation of visual hallucination is a bilateral flickering central distortion that then spreads to the periphery and leaves a residual central scotoma. Other etiologies of hallucinations with a classic presentation include visual snow, which involves a visual distortion causing the visual field to appear as if it were viewed on a static-filled television.
Psychosis is a feature of many psychiatric disorders and involves delusions, thought disorganization, and/or hallucinations. Some notable causes of primary psychosis include primary psychotic disorders, such as schizophrenia disorder, schizophreniform disorder, delusional disorders and brief psychotic disorders. While auditory hallucinations are more common among this group of patients, visual hallucinations may also present in a patient experiencing psychosis due to the aforementioned psychiatric illness. These visual hallucinations may be with preserved insight (i.e. reality testing is intact, and the patient recognizes that the hallucination is unreal) or without insight (i.e. reality testing is absent). Examples of visual hallucinations among patients with psychosis are visual hallucinations similar to migraine aura, sleep-related hallucinations (i.e. hypnagogic and hypnopompic hallucinations), and vibrant scenes involving family members, religious figures, and animals.
Delirium is characterized by an acute fluctuation in cognition and decreased consciousness in the absence of other neurocognitive disorders, and often is accompanied by visual hallucinations. Etiologies that may precipitate delirium include underlying medical conditions (i.e. metabolic encephalopathy), substance withdrawal, or medication side effect. Delirium is particularly common among elderly hospitalized patients. The contents of these visual hallucinations may range from simple shapes to perceptions of crawling insects, the latter of which is especially reported among patients experiencing delirium tremens secondary to alcohol withdrawal.
Migraines occur in 15-29% of the general population, and among those, 31% of patients report seeing visual auras in association with their migraines.  The most common presentation of a visual aura initially starts as a colorless, fortification flickering distortion in the central vision that gradually built and march to the periphery and leaves a residual central scotoma. The entirety of this visual phenomena typically lasts from less than 30 minutes. Additional information are detailed here: Ophthalmologic Manifestations of Migraines.
Seizures are characterized by aberrant neuronal activity occurring within the cortex of the brain and may present with visual hallucinations that often consist of flashing shapes or vibrant dots.  More complex visual hallucinations may be due to involvement of the visual association cortex. Additional information may be found here: Ophthalmologic Manifestations of Epilepsy.
Visual snow is a primarily neurological etiology of visual hallucination that consists of constant positive visual disturbances which are perceived as multiple small dots covering the entire visual field, creating a “static” effect. Additional information can be found here: Visual Snow.
Dementia, defined as the clinical syndrome characterized by significant losses of cognition and emotional ability, has various clinical subtypes which may be associated with visual hallucinations. Dementia with Lewy bodies (DLB) is the second most common type of dementia and includes visual hallucinations as a prominent symptom of the disease, occurring in up to 20% of patients with DLB. Other symptoms of DLB include parkinsonian movement disorders and decreased cognition. Up to 25% of Parkinson’s patients may also experience visual hallucinations, with common hallucinations including seeing animals or family members. Additional information regarding visual symptoms of Parkinson’s disease can be found here: Visual Symptoms of Parkinson’s Disease.
Posterior cortical atrophy is a rare neurodegenerative disease affecting the parietal and occipital lobes that often represents a variant of another neurodegenerative disease, such as Alzheimer’s disease or LBD. Patients with posterior cortical atrophy may present with early visual symptoms including visual agnosia and Gerstmann syndrome, with visual hallucinations being a less common manifestation of the disease.
Alzheimer’s disease (AD) may also be accompanied by visual hallucinations, with reported incidence of visual phenomena occurring in 12-53% of patients diagnosed with AD. Hallucinations are often associated with lower cognition scores and behavioral disturbances. Additional information can be found here: Visual Variant of Alzheimer’s disease.
Hypnagogic and hypnopompic hallucinations with intact consciousness may occur in conjunction with narcolepsy, a neurologic disorder characterized by atypical daytime sleepiness and disruptive rapid eye movement sleep stage. While auditory hallucinations are more common in narcolepsy than visual hallucinations, types of visual hallucinations experienced include passage types (i.e. brief visions of animal or person moving sideways) and presence types (perception of a living person or animal without actually seeing or touching it).
Hallucinogenic drugs, such as lysergic acid diethylamide (LSH), mescaline and psilocybin, may induce visual hallucinations at high doses, although mere alteration of perceptions are more common at lower doses. These drugs agonize 5-HT(2A) receptors, which is theorized to be responsible for their hallucinogenic effects.
A rare complication of prior hallucinogen use is known as Hallucinogen Persisting Perception Disorder (HPPD), which involves continual perceptual distortions lasting for months to years after cessation of the initial substance usage. More information regarding HPPD can be found here: Hallucinogen Persisting Perception Disorder.
Tumors located along the optic path or that induce compression may induce visual hallucinations. Common locations for tumors are in the temporal lobe, as evidenced by a case series that reported 13 of 59 patients with temporal lobe tumors experiencing visual hallucinations. Other potential locations for tumors include those that affect the parietal and occipital lobes.
Optic Nerve Damage
Patients with papilledema may experience simple visual hallucinations of flashing lights, likely due to transient irritation of retinal photoreceptors secondary to edema within the retinal ganglion axonal layer. Optic neuritis may also present with simple visual hallucinations as this visual phenomenon has been documented in up to 30% of patients with optic neuritis and are typically precipitated by eye movement.
Charles Bonnet Syndrome
Charles Bonnet Syndrome (CBS) is a disorder consisting of visual hallucinations occurring in patients with significant visual impairment secondary to primary ophthalmic disease (i.e. advanced macular degeneration, retinal detachment, glaucoma) or deafferentation of the visual cortex. CBS patients notably have intact cognition. Visual hallucinations experienced by patients with CBS are highly variable and range from simple flashes of light to complex images of people or animals. Additional information can be found here: Charles Bonnet Syndrome.
Peduncular hallucinosis is a rare type of visual hallucination thought to be secondary to ischemic lesions in the thalamus and midbrain. These hallucinations often consist of vibrant visions of animals and people. Patients with peduncular hallucinosis often have insight into their hallucinations, despite difficulty distinguishing the complex hallucination from reality. Additional information can be found here: Peduncular Hallucinosis.
Alice in Wonderland Syndrome
Alice in Wonderland Syndrome (AIWS) is a rare neuro-ophthalmologic disorder characterized by alteration of body image due to distortions in visual perception. While the exact causes of AIWS are unknown, there are presumed associations with migraines, temporal lobe epilepsy, brain tumors and Epstein-Barr-Virus (EBV) infections. Additional information regarding AIWS can be found here: Alice in Wonderland Syndrome.
Anton-Babinski syndrome (Anton syndrome) is characterized by visual anosognosia (denial of vision loss) in association with confabulations in the setting of severe vision loss, either due to primary ophthalmic disease or cortical blindness. Anton syndrome is most commonly secondary to cerebrovascular accident and is therefore detected more commonly among elderly patients. More information can be found here: Anton Syndrome.
Hallucinatory palinopsia is a perceptual distortion where high-resolution images persist or recur for long periods of time after the visual stimulus. Palinopsia is thought to occur in association with brain tumors, epilepsy, and drug usage. Additional information can be found here: Palinopsia.
Other rare causes of visual hallucinations include post-concussive syndrome (Neuro-Ophthalmic Manifestations of Post-Concussion Syndrome), reversible posterior leukoencephalopathy syndrome (Reversible Posterior Leukoencephalopathy Syndrome), certain inborn errors of metabolism (i.e. homocysteine remethylation defects, urea cycle defects, GM2 gangliosidosis, Neimann-Pick disease type C, and α-mannosidosis), Creutzfeldt-Jakob Disease (Ophthalmologic Manifestations of Creuzfeldt-Jakob), and Familial Fatal Insomnia (Ophthalmologic Manifestations in Fatal Familial Insomnia).
Medical therapy should be used only to manage the pathologic underpinnings of the systemic disease that led to visual hallucination, and not for the hallucination itself. Psychosis and delirium are often managed with environmental alterations, inciting drug discontinuation (if appropriate) and anti-psychotic medications (i.e. typical antipsychotics, such as haloperidol). Migraines may be managed acutely with NSAIDs, triptans, as well as chronically with beta blockers, topiramate, and other prophylactic medications. Seizure disorders are managed with appropriate anti-epileptic drug regimens specific to the underlying etiology for seizure. The treatment for optic nerve damage is highly contingent on the cause of damage, and may involve appropriate treatment for underlying infection or inflammation. More information on the management of some optic nerve disorders can be found here: Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION), Diagnostic Approach to Atypical Optic Neuritis, Demyelinating Optic Neuritis. For additional information regarding the medical management of other causes of visual hallucination, please refer to the following links: Charles Bonnet Syndrome; Peduncular Hallucinosis; Alice in Wonderland Syndrome; Anton Syndrome; Palinopsia; manifestations of post-concussion syndrome (Neuro-Ophthalmic Manifestations of Post-Concussion Syndrome), reversible posterior leukoencephalopathy (Reversible Posterior Leukoencephalopathy Syndrome), inborn errors of metabolism, Creutzfeldt-Jakob Disease (Ophthalmologic Manifestations of Creuzfeldt-Jakob), familial fatal insomnia (Ophthalmologic Manifestations in Fatal Familial Insomnia)
While the visual hallucination itself does not impact visual function, it may portend poor visual outcomes depending on the etiology of the hallucination. Furthermore, certain pathologies that induce visual hallucinations, such as Creutzfeld-Jakob Disease, have a rapid disease course with high mortality rates. However, other causes such as visual snow are benign and have very good visual prognoses. Further information regarding the prognosis related to the specific underlying cause of visual hallucination can be found here: migraines; epilepsy; visual snow; dementia, Visual Variant of Alzheimer’s Disease; drug effects; Charles Bonnet Syndrome; Peduncular Hallucinosis; Alice in Wonderland Syndrome; Anton Syndrome; Palinopsia.
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