Visual Snow Syndrome

Key points at a glance

Main points of this condition

• Visual snow syndrome (VSS) is a neuro-ophthalmic disorder in which tiny flickering dots appear continuously in both eyes across the entire visual field, like television static.
• The diagnostic criteria (Schankin et al. 2014) require visual snow to persist for more than 3 months and to meet at least 3 of 4 additional visual symptoms.
• Migraine is present in 30–60% of cases, and the prevalence is about twice that of the general population, but it is established as an independent disorder distinct from persistent migraine aura.
• It is important that routine eye examinations (visual acuity, visual field, ERG, OCT) are usually normal.
• Neuroimaging has reported increased gray matter and increased metabolism in the lingual gyrus, as well as increased gamma-wave power in the primary visual cortex, suggesting that cortical hyperexcitability and an imbalance between excitation and inhibition are central to the condition.
• No established standard treatment exists, and reports have described attempts with lamotrigine, benzodiazepines, etc., but effectiveness is limited.
• Most cases follow a chronic, persistent course, and reports of spontaneous remission are limited.

What is Visual Snow Syndrome?

Visual Snow Syndrome (VSS) is a neuro-ophthalmic disorder in which bilateral, persistent, dynamic flickering dots appear across the entire visual field ²⁾. Patients often describe it as “snow,” “TV static,” or a “pixelated screen.” The dots are usually black and white, but can also be colored, transparent, or flash-like. It is generally more noticeable against plain backgrounds and less noticeable against textured backgrounds.

It was once considered a persistent migraine aura, but is now established as an independent disease concept ¹⁾. Some patients notice it lifelong from childhood, and there are also acute-onset cases. Distinguishing primary (unknown cause) from secondary (due to drugs or neurological disease) is important for diagnosis.

Diagnostic criteria

The Schankin et al. (2014) diagnostic criteria ¹⁾, which are currently the most widely used, consist of the following four items.

1. Visual snow (flickering dots) persists for 3 months or longer
2. Accompanied by at least 3 of the following additional visual symptoms
   • Palinopsia (persistent afterimages)
   • Photophobia
   • Nyctalopia (night blindness)
   • Increased entoptic phenomena (floaters, photopsia, blue field entoptic phenomenon, self-light of the eye)
3. Cannot be explained by migraine aura alone
4. Cannot be explained by other diseases (ophthalmic or neurological)

Q Is visual snow the same as a migraine aura?

A

It is a different disease concept. Migraine aura is episodic (lasting 5 to 60 minutes), whereas VSS is persistent. Although migraine is common in 30% to 60% of cases, VSS persists independently of migraine attacks, so it is treated as a separate condition.

2. Main symptoms and clinical findings

Visual symptoms

Visual snow (core symptom): Tiny flickering dots across the entire visual field. They are often black and white, but may also be colored or transparent. They persist in both dim and bright light.

Palinopsia: An image persists as an afterimage even after the visual stimulus has disappeared. It is thought to be caused by abnormally persistent visual memory.

Photophobia: Painful sensitivity to light. It can significantly reduce quality of life.

Nyctalopia: Reduced night vision. It is thought to be related to abnormal regulation of visual input and dysfunction of cone-rod interactions³⁾.

Increased entoptic phenomena: floaters, spontaneous flashes of light, blue field entoptic phenomenon (the perception of white blood cells moving when looking at a blue sky), and self-light of the eye (a swirling light sensation in the dark) become more pronounced.

Non-visual symptoms

Migraine: It co-occurs in about 50%. In the same study, migraine was found in 54.1% of the non-drug-induced VSS group, about twice the rate in the general population, and the proportion of patients with migraine with visual aura was high⁴⁾.

Tinnitus: High-pitched, persistent tinnitus is common, and it is thought to be caused by increased spontaneous activity in the subcortical auditory pathways. It may worsen with focused attention.

Hyperacusis, cutaneous allodynia, and tremor: Sensory hypersensitivity may involve multiple modalities⁵⁾.

Psychosocial impact: Difficulty concentrating, fatigue, depression, anxiety, and balance problems have been reported^{6, 7)}.

Clinical findings (importance of normal findings)

In a systematic neuro-ophthalmologic evaluation of 20 cases by Yoo et al., all of the following were confirmed to be normal⁶⁾.

• Corrected visual acuity and autorefraction
• Slit-lamp examination and dilated fundus examination
• Visual field testing and contrast sensitivity
• Pupillary light reflex
• Full-field ERG and multifocal ERG
• OCT (RNFL thickness)

It is characteristic of this condition that almost all cases show normal findings on routine ophthalmologic and neuro-ophthalmologic examinations.

Q Why do symptoms occur even though there are no abnormalities on eye exams?

A

VSS is thought to be a disorder of visual information processing at the cortical level, rather than a disease of the eye itself. Dysfunction is presumed to be posterior to the lateral geniculate body (at the cerebral cortex level), and it cannot be detected with routine eye examinations. Cortical hyperexcitability in the lingual gyrus and primary visual cortex is thought to underlie the symptoms.

3. Causes and risk factors

Most cases are primary (of unknown cause). A history of migraine, especially with aura, is considered an important risk factor.

Secondary triggers

Drug-related: VSS triggered by methylphenidate has been reported, and some cases improved after switching to atomoxetine²⁵⁾. Alcohol and recreational drugs can worsen or trigger symptoms.

HPDD (hallucinogen persisting perception disorder): Similar symptoms can occur in patients with a history of hallucinogen use. The symptoms resemble VSS, but the mechanism of onset is different, and confirming the drug history during the interview is key to distinguishing it.

Repetitive mild traumatic brain injury: VSS may be seen after concussion or mild traumatic brain injury, and neuro-visual function evaluation and treatment selection are being considered⁵⁾.

Cerebellar infarction: Conversion from episodic to chronic VSS has been reported after infarction in the superior cerebellar artery territory¹⁸⁾.

Expert note

VSS symptoms can worsen with attention and concentration. Carelessly labeling it as purely psychogenic can undermine trust with the patient. Putting a stigmatizing label on VSS may worsen the patient’s distress, so careful wording is needed.

4. Diagnosis and testing

Clinical diagnostic process

A definitive diagnosis is based on a detailed medical history. At present, there is no specific confirmatory test.

Items to confirm in the medical history:

• Whether visual snow is persistent or intermittent
• Whether there were triggers before onset (infection, medication, trauma, etc.)
• Whether there are additional visual symptoms (palinopsia, photophobia, night blindness, entoptic phenomena) and how many
• Whether there are non-visual symptoms (tinnitus, migraine)
• Factors that worsen the symptoms
• Use of recreational drugs (especially hallucinogens)
• History of migraine (especially with aura)

Neuroimaging (research-level findings)

Not an essential test in routine clinical practice, but the following findings have been reported in research.

Test	Main findings	References
fMRI	Hyperconnectivity between posterior lateral temporal, frontal, and parietal areas; increased gray matter in the right lingual gyrus	Aldusary 202010)
FDG-PET	Increased metabolism in the right lingual gyrus, decreased metabolism in the superior temporal gyrus and inferior parietal lobule	Schankin 202011)
MEG	Increased gamma-wave (40–70 Hz) power in the primary visual cortex, reduced alpha-gamma phase-amplitude coupling	Hepschke 202112)
DTI	Abnormalities in the frontal, temporal, and occipital white matter, with changes in the superior longitudinal fasciculus, middle longitudinal fasciculus, and sagittal stratum	Michels 202113)
Quantitative MRI	Lower T1 values in the cerebral cortical gray matter, thalamus, globus pallidus, and putamen	Strik 202230)
ASL-MRI	Increased regional cerebral blood flow in the cuneus, precuneus, posterior cingulate cortex, and other areas at rest and during visual stimulation	Puledda 202216)

Differential diagnosis

Visual Snow Syndrome

Persistence: lasting for more than 3 months

Extent: bilateral, full visual field

Additional symptoms: three or more items, including palinopsia

Ophthalmic examination: normal findings

Migraine aura

Duration: episodic (5–60 minutes)

Visual symptoms: positive symptoms such as scintillating scotoma

Relation to headache: precedes or accompanies it

Course: resolves spontaneously

HPPD (Hallucinogen Persisting Perception Disorder)

Required condition: history of hallucinogen use

Symptoms: similar to VSS

Mechanism of onset: drug-induced

Key differential point: detailed review of medication history

Other differentials include bilateral optic neuropathy (methanol poisoning, ischemia, LHON, folate/B12 deficiency) and bilateral retinal disease⁸⁾.

Warning signs requiring further evaluation (organic disease must be ruled out):

• New onset (especially in older adults)
• Intermittent or sudden worsening
• Unilateral or hemifield visual snow
• No additional visual symptoms
• History of ophthalmic or neurological disease

Note

If onset is rapid or one-sided, it is essential to rule out organic disease (optic neuropathy, retinal disease, cerebrovascular disease). Neuroimaging such as MRI should be actively considered.

Q What tests are needed to diagnose visual snow?

A

There is currently no specific confirmatory test. Diagnosis is based on history taking and exclusion. Normal routine ophthalmic tests (visual acuity, visual field, ERG, OCT) can actually be a clue to the diagnosis. If onset is acute or unilateral, MRI is used to rule out organic disease.

5. Standard treatments

Important: There is currently no established standard treatment. The pathophysiology is also not yet understood, and treatments based on the disease mechanism and RCTs have not yet been conducted.

Drug therapy

In a survey of 400 VSS patients by Puledda et al.²¹⁾, the following drugs were reported to have relatively high improvement rates.

• Benzodiazepines/hypnotics
• Triptans
• Lamotrigine (an antiepileptic drug. It has been tried most often, but there is also a risk of symptom worsening, and the improvement rate did not differ significantly from other drugs)
• Tricyclic antidepressants
• Gabapentin
• Beta blockers
• Topiramate (worsening has been reported in some cases. Exacerbation has been reported in pediatric cases²⁶⁾)
• Vitamins/nutritional supplements

In individual case reports, lamotrigine 25 mg/day, topiramate 25 mg/day, acetazolamide 750 mg/day, and propranolol 20 mg/day (2 cases each) were all ineffective⁶⁾.

Drugs to watch for:

• Atypical antidepressants and ADHD medications (such as methylphenidate): may carry a risk of worsening
• Alcohol and recreational drugs: may worsen or trigger symptoms

Cautions

No drug has been shown to be sufficiently effective. The evidence for all of them is limited to case reports and small studies, and there is also a risk that symptoms may worsen. If drug therapy is started, begin with a low dose and carefully assess the effect and side effects (especially worsening of visual symptoms). Not all patients want drug therapy, and many are very concerned about side effects.

Non-drug treatments

Color filters / tinted lenses: Reports suggest that FL-41 glasses and yellow-blue spectrum filters may help light sensitivity²⁴⁾. Blue-violet light may selectively increase excitation of S-cones (short-wavelength-sensitive cones) and worsen symptoms¹⁹⁾.

Repetitive transcranial magnetic stimulation (rTMS): 10+1 Hz rTMS has been reported to reduce the total visual-snow intensity score after 1 week (n=9)²²⁾. In another open-label feasibility trial protocol, enrollment of up to 10 cases was planned, but the paper did not report efficacy results²³⁾.

Phenylephrine eye drops: A case report described partial improvement in night blindness²⁴⁾.

Patient support

• Explaining that this is a benign condition is the most important step
• Do not conclude that it is purely psychogenic
• Guidance to avoid factors that can worsen symptoms (alcohol, recreational drugs, certain medications)
• Support the patient’s coping strategies

Q Can visual snow syndrome be cured?

A

Reports of spontaneous remission are limited, and most cases follow a chronic, persistent course. There is no established treatment, but symptom improvement has been reported in some patients with lamotrigine, rTMS, and other approaches. Color filter lenses may help relieve light sensitivity. A realistic goal is to keep quality of life as high as possible while living with the symptoms.

6. Pathophysiology and detailed mechanism of onset

Although the pathophysiology remains unclear, findings from multiple neuroimaging studies have accumulated as follows.

Evidence for a central origin

Because visual snow appears across the entire visual field, its source is thought to be behind the lateral geniculate nucleus, where visual input from both eyes is integrated, at the level of the cerebral cortex⁹⁾. Normal eye examinations also support this. It is considered a problem in visual information processing rather than a structural problem.

Abnormalities in the lingual gyrus

The lingual gyrus is a region involved in visual postprocessing, and consistent abnormalities have been reported in VSS.

• FDG-PET: increased metabolism in the right lingual gyrus¹¹⁾
• VBM (brain morphometry): increased gray matter volume in the right lingual gyrus. Positively correlated with symptom duration¹⁰⁾
• MRS (magnetic resonance spectroscopy): increased lactate concentration in the right lingual gyrus¹⁴⁾

Cortical hyperexcitability and imbalance between excitation and inhibition

Studies using MEG have shown increased gamma-wave (40–70 Hz) power and reduced alpha-gamma phase-amplitude coupling in the primary visual cortex, suggesting dysfunction of the visual cortex noise-canceling mechanism¹²⁾.

On the other hand, magnetic suppression perceptual accuracy (MSPA) is normal in VSS, suggesting that inhibition itself in the primary visual cortex may be preserved²⁰⁾.

Network dysfunction

This is characterized by impairment across multiple networks rather than a single structural abnormality.

• fMRI: abnormal connectivity within the visual pathways, attention network, and salience network¹⁵⁾
• Reduced BOLD response of the insular cortex to visual stimuli¹⁴⁾
• Increased local cerebral blood flow: widespread regions involved in complex sensory processing (cuneus, precuneus, premotor cortex, posterior cingulate cortex, left primary auditory cortex, etc.)¹⁶⁾
• DTI: microstructural changes in the frontal, temporal, and occipital white matter (changes in the superior longitudinal fasciculus, middle longitudinal fasciculus, and sagittal stratum)¹³⁾
• Involvement of the cerebellum (gray matter changes, chronicity after cerebellar infarction)^{17, 18)}

Cone pathway involvement

It has been shown that symptoms worsen with color modulation that selectively increases S-cone (short-wavelength-sensitive “blue” cone) excitation¹⁹⁾, and a hypothesis has been proposed that modulation of the koniocellular (KC) pathway increases parvocellular and magnocellular pathway activity, bringing subthreshold visual stimuli into conscious awareness.

Integrated hypothesis

Central hyperexcitability/cortical disinhibition and disruption of sensory processing and attention networks are thought to underlie visual snow. The “stochastic resonance” hypothesis suggests that internally generated visual signals below threshold, which are normally suppressed, may rise to awareness, and may also explain worsening tinnitus, photophobia, and intraocular phenomena.

7. Latest research and future prospects (research-stage reports)

For patients: Please read carefully

The following content is still at the research stage or in clinical trials and is not standard treatment available at ordinary hospitals. It is reference information for specialists about future medical developments.

Objective assessment using a saccade behavior profile

In a series of studies by Solly et al., eye movement tasks (prosaccade/antisaccade/IOR) are used to objectively evaluate changes in visual processing in patients with VSS.

Shortened prosaccade latency²⁷⁾, increased antisaccade errors²⁸⁾, and delayed onset of inhibition of return (IOR)²⁹⁾ have been reported, suggesting potential as objective indicators for future treatment-response monitoring.

Development of rTMS treatment

In the trial by Grey et al. (n=9), 10+1 Hz rTMS significantly reduced the total VS intensity after 1 week²²⁾. Grande et al. reported a non-blinded feasibility trial protocol involving up to 10 cases, but the paper did not report efficacy results²³⁾. The safety and efficacy of noninvasive brain stimulation for the visual cortex remain under investigation.

Future challenges

• Conducting large-scale prospective studies and RCTs
• Establishing objective biomarkers (saccade profiles and neuroimaging markers)
• Developing treatment strategies based on disease mechanisms (such as drugs targeting cortical hyperexcitability)
• Standardizing patient quality-of-life assessment measures

8. References

1. Schankin CJ, Maniyar FH, Digre KB, Goadsby PJ. ‘Visual snow’—a disorder distinct from persistent migraine aura. Brain. 2014;137(Pt 5):1419-1428. doi:10.1093/brain/awu050.

2. Puledda F, Schankin C, Digre K, Goadsby PJ. Visual snow syndrome: what we know so far. Current opinion in neurology. 2018;31(1):52-58. doi:10.1097/WCO.0000000000000523. PMID:29140814.

3. Schankin CJ, Goadsby PJ. Visual snow—persistent positive visual phenomenon distinct from migraine aura. Current pain and headache reports. 2015;19(6):23. doi:10.1007/s11916-015-0497-9. PMID:26021756.

4. Van Dongen RM, Alderliefste GJ, Onderwater GLJ, et al. Migraine prevalence in visual snow with prior illicit drug use (hallucinogen persisting perception disorder) versus without. Eur J Neurol. 2021;28(8):2631-2638. doi:10.1111/ene.14914.

5. Ciuffreda KJ, Han ME, Tannen B, Rutner D. Visual snow syndrome: evolving neuro-optometric considerations in concussion/mild traumatic brain injury. Concussion (London, England). 2021;6(2):CNC89. doi:10.2217/cnc-2021-0003. PMID:34084555; PMCID:PMC8162163.

6. Yoo YJ, Yang HK, Choi JY, Kim JS, Hwang JM. Neuro-ophthalmologic Findings in Visual Snow Syndrome. J Clin Neurol. 2020;16(4):646-652. doi:10.3988/jcn.2020.16.4.646.

7. White OB, Clough M, McKendrick AM, Fielding J. Visual Snow: Visual Misperception. Journal of neuro-ophthalmology : the official journal of the North American Neuro-Ophthalmology Society. 2018;38(4):514-521. doi:10.1097/WNO.0000000000000702. PMID:30095537.

8. Barral E, Martins Silva E, García-Azorín D, Viana M, Puledda F. Differential Diagnosis of Visual Phenomena Associated with Migraine: Spotlight on Aura and Visual Snow Syndrome. Diagnostics (Basel, Switzerland). 2023;13(2). doi:10.3390/diagnostics13020252. PMID:36673062; PMCID:PMC9857878.

9. Eren O, Schankin CJ. Insights into pathophysiology and treatment of visual snow syndrome: A systematic review. Progress in brain research. 2020;255:311-326. doi:10.1016/bs.pbr.2020.05.020. PMID:33008511.

10. Aldusary N, Traber GL, Freund P, Fierz FC, Weber KP, Baeshen A, et al. Abnormal Connectivity and Brain Structure in Patients With Visual Snow. Frontiers in human neuroscience. 2020;14:582031. doi:10.3389/fnhum.2020.582031. PMID:33328934; PMCID:PMC7710971.

11. Schankin CJ, Maniyar FH, Chou DE, Eller M, Sprenger T, Goadsby PJ. Structural and functional footprint of visual snow syndrome. Brain : a journal of neurology. 2020;143(4):1106-1113. doi:10.1093/brain/awaa053. PMID:32211752; PMCID:PMC7534145.

12. Hepschke JL, Seymour RA, He W, Etchell A, Sowman PF, Fraser CL. Cortical oscillatory dysrhythmias in visual snow syndrome: a magnetoencephalography study. Brain communications. 2022;4(1):fcab296. doi:10.1093/braincomms/fcab296. PMID:35169699; PMCID:PMC8833316.

13. Michels L, Stämpfli P, Aldusary N, Piccirelli M, Freund P, Weber KP, et al. Widespread White Matter Alterations in Patients With Visual Snow Syndrome. Frontiers in neurology. 2021;12:723805. doi:10.3389/fneur.2021.723805. PMID:34621237; PMCID:PMC8490630.

14. Puledda F, Ffytche D, Lythgoe DJ, O’Daly O, Schankin C, Williams SCR, et al. Insular and occipital changes in visual snow syndrome: a BOLD fMRI and MRS study. Annals of clinical and translational neurology. 2020;7(3):296-306. doi:10.1002/acn3.50986. PMID:32154676; PMCID:PMC7086005.

15. Puledda F, O’Daly O, Schankin C, Ffytche D, Williams SC, Goadsby PJ. Disrupted connectivity within visual, attentional and salience networks in the visual snow syndrome. Human brain mapping. 2021;42(7):2032-2044. doi:10.1002/hbm.25343. PMID:33448525; PMCID:PMC8046036.

16. Puledda F, Schankin CJ, O’Daly O, Ffytche D, Eren O, Karsan N, et al. Localised increase in regional cerebral perfusion in patients with visual snow syndrome: a pseudo-continuous arterial spin labelling study. Journal of neurology, neurosurgery, and psychiatry. 2021;92(9):918-926. doi:10.1136/jnnp-2020-325881. PMID:34261750; PMCID:PMC8372400.

17. Puledda F, Bruchhage M, O’Daly O, Ffytche D, Williams SCR, Goadsby PJ. Occipital cortex and cerebellum gray matter changes in visual snow syndrome. Neurology. 2020;95(13):e1792-e1799. doi:10.1212/WNL.0000000000010530. PMID:32759201; PMCID:PMC7682819.

18. Puledda F, Villar-Martínez MD, Goadsby PJ. Case Report: Transformation of Visual Snow Syndrome From Episodic to Chronic Associated With Acute Cerebellar Infarct. Frontiers in neurology. 2022;13:811490. doi:10.3389/fneur.2022.811490. PMID:35242098; PMCID:PMC8886039.

19. Hepschke JL, Martin PR, Fraser CL. Short-Wave Sensitive (“Blue”) Cone Activation Is an Aggravating Factor for Visual Snow Symptoms. Front Neurol. 2021;12:697923. doi:10.3389/fneur.2021.697923.

20. Eren OE, Ruscheweyh R, Rauschel V, Eggert T, Schankin CJ, Straube A. Magnetic Suppression of Perceptual Accuracy Is Not Reduced in Visual Snow Syndrome. Frontiers in neurology. 2021;12:658857. doi:10.3389/fneur.2021.658857. PMID:34017304; PMCID:PMC8129492.

21. Puledda F, Vandenbussche N, Moreno-Ajona D, Eren O, Schankin C, Goadsby PJ. Evaluation of treatment response and symptom progression in 400 patients with visual snow syndrome. The British journal of ophthalmology. 2022;106(9):1318-1324. doi:10.1136/bjophthalmol-2020-318653. PMID:34656983; PMCID:PMC9411880.

22. Grey V, Klobusiakova P, Minks E. Can repetitive transcranial magnetic stimulation of the visual cortex ameliorate the state of patients with visual snow? Bratisl Med J. 2020;121(6):395-399.

23. Grande M, Lattanzio L, Buard I, McKendrick AM, Chan YM, Pelak VS. A Study Protocol for an Open-Label Feasibility Treatment Trial of Visual Snow Syndrome With Transcranial Magnetic Stimulation. Frontiers in neurology. 2021;12:724081. doi:10.3389/fneur.2021.724081. PMID:34630299; PMCID:PMC8500216.

24. Coleman W, Sengupta S, Boisvert CJ. A case of visual snow treated with phenylephrine. Headache. 2021;61(5):792-793. doi:10.1111/head.14118. PMID:34021593.

25. Naguy AM, Naguy C, Singh AM. Probable Methylphenidate-Related Reversible “Visual Snow” in a Child With ADHD. Clin Neuropharmacol. 2022;45(4):105-106. doi:10.1097/wnf.0000000000000512.

26. Guay M, Lagman-Bartolome AM. Onset of Visual Snow Syndrome After the First Migraine Episode in a Pediatric Patient: A Case Report and Review of Literature. Pediatr Neurol. 2022;126:46-49. doi:10.1016/j.pediatrneurol.2021.08.005.

27. Solly EJ, Clough M, McKendrick AM, Foletta P, White OB, Fielding J. Ocular motor measures of visual processing changes in visual snow syndrome. Neurology. 2020;95(13):e1784-e1791. doi:10.1212/WNL.0000000000010372. PMID:32675081.

28. Solly EJ, Clough M, McKendrick AM, Foletta P, White OB, Fielding J. Eye movement characteristics provide an objective measure of visual processing changes in patients with visual snow syndrome. Scientific reports. 2021;11(1):9607. doi:10.1038/s41598-021-88788-2. PMID:33953220; PMCID:PMC8099863.

29. Foletta PJ, Clough M, McKendrick AM, Solly EJ, White OB, Fielding J. Delayed Onset of Inhibition of Return in Visual Snow Syndrome. Frontiers in neurology. 2021;12:738599. doi:10.3389/fneur.2021.738599. PMID:34603190; PMCID:PMC8484518.

30. Strik M, Clough M, Solly EJ, Glarin R, White OB, Kolbe SC, et al. Microstructure in patients with visual snow syndrome: an ultra-high field morphological and quantitative MRI study. Brain communications. 2022;4(4):fcac164. doi:10.1093/braincomms/fcac164. PMID:35974797; PMCID:PMC9373960.