Visual snow syndrome
Other namesPersistent positive visual phenomenon,[1] visual static, aeropsia
Animated example of visual snow-like noise
SpecialtyNeurology, Neuro-ophthalmology
SymptomsStatic and auras in vision, Palinopsia, Blue field entoptic phenomenon, Nyctalopia, Tinnitus
ComplicationsPoor quality of vision, Photophobia, Heliophobia, Depersonalization and Derealization[2]
Usual onsetVisual Snow can appear at any time, but it commonly appears at birth, late teenage years, and early adulthood.
CausesUnknown,[3] hyperexcitability of neurons and processing problems in the visual cortex[4][5]
Risk factorsMigraine sufferer,[6] psychoactive substance use
Differential diagnosisMigraine aura,[7] Persistent aura without infarction, Hallucinogen persisting perception disorder[8][9]
MedicationAnticonvulsants[7][3] (limited evidence and success)
FrequencyUncommon (understudied)

Visual snow syndrome (VSS) is a form of visual hallucination that is characterized by the perception of small, bilateral, simultaneous, diffuse, mobile, asynchronous dots usually throughout the entire visual field, but it can be partial, and it is present in all conditions of illumination. The dots remain individual and do not clump together or change in size. Visual snow exists in one of two forms: the pulse type and the broadband type.

In the Pulse type the dots are the same color as their background, black or white, and the noise is monopolar. In black pulse visual snow, the dots are always darker than their background, whereas in white pulse the dots are always lighter than their background.

In the Broadband type the dots noise is bipolar and occurs in contrast to the background: with a light background the dots will appear dark, and with a dark background the dots will appear light.[7][4]

Other common symptoms are palinopsia, enhanced entoptic phenomena, photophobia, and tension headaches.[10][11] The condition is typically always present and has no known cure, as viable treatments are still under research.[12] Astigmatism, although not presumed connected to these visual disturbances, is a common comorbidity. As well, migraine and tinnitus are common comorbidities which are both associated with a more severe presentation of the syndrome.[13] TMJ may also be a common comorbidity.

The cause of the syndrome is unclear.[3] The underlying mechanism is believed to involve excessive excitability of neurons in the right lingual gyrus and left anterior lobe of cerebellum. Another hypothesis proposes that visual snow syndrome could be a type of thalamocortical dysrhythmia and may involve the thalamic reticular nucleus (TRN). A failure of inhibitory action from the TRN to the thalamus may be the underlying cause for inability to suppress excitatory sensory information.[4][6] Research has been limited due to issues of case identification and diagnosis, the latter now largely addressed, and the limited size of any studied cohort. Initial functional brain imaging research suggests visual snow is a brain disorder.

There is no established treatment for visual snow syndrome. Medications that may be used to treat the condition include lamotrigine, acetazolamide, or verapamil.[4] However, in absence of a secondary pharmaceutical indication, these do not necessarily result in benefits, and the evidence for their use is limited.[7][3]

Signs and symptoms

Normal vision vis-à-vis disturbed vision

In addition to visual snow, many of those affected have other types of visual disturbances such as starbursts, increased afterimages, floaters, trails, and many others.[14]

Visual snow likely represents a clinical continuum, with different degrees of severity. The presence of comorbidities such as migraine and tinnitus is associated with a more severe presentation of the visual symptoms.[13]

Diagnosis

Visual snow syndrome is usually diagnosed with the following proposed criteria:[15][16][13]

  • Visual snow: dynamic, continuous, tiny dots observed across the entire visual field at any time of the day, regardless of lighting conditions, persisting for more than three months.
    • The dots are usually black/gray on a white background and gray/white on a black background; however, they can also be transparent, white flashing, or colored.
  • Presence of at least 2 additional visual symptoms of the 4 following categories:
  • Symptoms are not consistent with typical migraine aura.
  • Symptoms are not better explained by another disorder (ophthalmological, drug abuse).

Additional and non visual symptoms like tinnitus, ear pressure or brain fog and more might be present. It can also be diagnosed by PET scan.

What is not visual snow?

  1. Perceiving visual static, flickering, or graininess on monochrome colors, in the sky, or in darkness can be a normal phenomenon associated with neural noise, amplified in the absence of bright visual stimuli. This effect is known as the Ganzfeld Effect (Wiki)/ Ganzfeld Effect (External Source). In conditions of low illumination, especially in dimly lit environments, this phenomenon is related to how the eyes and the brain process visual information in insufficient lighting. The visual system becomes more sensitive to light and can amplify noise or minor changes in visual signals. It's important to note that the perception of such phenomena may vary among different individuals due to individual differences in perception and sensitivity.
  2. When the eyes are closed, visual static may be related to the first level of visual hallucination.
  3. Eye pathologies or other neurological conditions can also be a cause of visual anomalies, including the appearance of visual static or other changes in perception.

Comorbidities

Migraine and migraine with aura are common comorbidities. However, comorbid migraine worsens some of the additional visual symptoms and tinnitus seen in "visual snow" syndrome. This might bias research studies by patients with migraine being more likely to offer study participation than those without migraine due to having more severe symptoms. In contrast to migraine, comorbidity of typical migraine aura does not appear to worsen symptoms.[6]

Psychological side effects of visual snow can include depersonalization, derealization, depression, photophobia and heliophobia in the individual affected.[2]

Patients with visual "snow" have normal equivalent input noise levels and contrast sensitivity.[17] In a 2010 study, Raghaven et al. hypothesize that what the patients see as "snow" is eigengrau.[17] This would also explain why many report more visual snow in low light conditions: "The intrinsic dark noise of primate cones is equivalent to ~4000 absorbed photons per second at mean light levels; below this the cone signals are dominated by intrinsic noise".[18]

Causes

The causes are unclear.[3] The underlying mechanism is believed to involve excessive excitability of neurons within the cortex of the brain,[4] specifically the right lingual gyrus and left cerebellar anterior lobe of the brain.[6]

Persisting visual snow can feature as a leading addition to a migraine complication called persistent aura without infarction,[19] commonly referred to as persistent migraine aura (PMA). In other clinical sub-forms of migraine headache may be absent and the migraine aura may not take the typical form of the zigzagged fortification spectrum (scintillating scotoma), but manifests with a large variety of focal neurological symptoms.[20]

Visual snow does not depend on the effect of psychotropic substances on the brain.[13] Hallucinogen persisting perception disorder (HPPD), a condition caused by hallucinogenic drug use, is sometimes linked to visual snow,[21] but both the connection of visual snow to HPPD[8] and the cause and prevalence of HPPD is disputed.[9] Most of the evidence for both is generally anecdotal, and subject to spotlight fallacy.[8][9]

Timeline

  • In May 2015, visual snow was described as a persisting positive visual phenomenon distinct from migraine aura in a study by Schankin and Goadsby.[22]
  • In December 2020, a study[23] found local increases in regional cerebral perfusion in patients with visual snow syndrome.
  • In September 2021, two studies[24] found white matter alterations in parts of the visual cortex and outside the visual cortex in patients with visual snow syndrome.

Treatments

It is difficult to resolve visual snow with treatment, but it is possible to reduce symptoms and improve quality of life through treatment, both of the syndrome and its comorbidities.[4] Medications that may be used include lamotrigine, acetazolamide, verapamil,[4]clonazepam or propranolol but these do not always result in benefits.[7][3] As of 2021, there were two ongoing clinical trials using transcranial magnetic stimulation and neurofeedback for visual snow.[25][26]

A recent study in the British Journal of Ophthalmology has confirmed that common drug treatments are generally ineffective in visual snow syndrome (VSS). Vitamins and benzodiazepines, however, were shown to be beneficial in some patients and can be considered safe for this condition.[27]

Victoria Pelak, a Professor of Neurology and Ophthalmology in the Department of Neurology at the University of Colorado Anschutz Medical Campus has recently directed, published, and completed enrollment for a TMS study protocol. The study protocol aims to investigate the use of rTMS intervention to improve symptoms and visual dysfunction associated with visual snow (VS); the study protocol also describes the challenges during the COVID-19 pandemic.[28]

In addition, Pelak described during her practice that she lets patients know that current treatment options are only limited to alleviating symptoms. She recommends that her patients focus on pharmaceutical and non-pharmaceutical treatments to control migraine, headaches, anxiety, and depression. As for light sensitivity complications, Pelak advises patients to use FL-41 tinted lenses indoors. She also recommends visual occupational therapists who assist patients with color-tinted lenses to alleviate VSS symptoms. Furthermore, Pelak states that exercising, meditation, and a healthy balanced diet can improve overall daily functioning.[29]

References

  1. ↑ Licht, Joseph; Ireland, Kathryn; Kay, Matthew. "Visual Snow: Clinical Correlations and Workup A Case Series". researchgate.net. Larkin Community Hospital. Retrieved 3 September 2017.
  2. 1 2 "Diagnostic Criteria | Visual Snow Initiative". 23 March 2023.
  3. 1 2 3 4 5 6 Brodsky, Michael C. (2016). Pediatric Neuro-Ophthalmology. Springer. p. 285. ISBN 9781493933846.
  4. 1 2 3 4 5 6 7 Bou Ghannam, A; Pelak, VS (March 2017). "Visual snow: a potential cortical hyperexcitability syndrome". Current Treatment Options in Neurology. 19 (3): 9. doi:10.1007/s11940-017-0448-3. PMID 28349350. S2CID 4829787.
  5. ↑ Bou Ghannam, A.; Pelak, V. S. (2017). "Visual Snow: A Potential Cortical Hyperexcitability Syndrome". Current Treatment Options in Neurology. 19 (3): 9. doi:10.1007/s11940-017-0448-3. PMID 28349350. S2CID 4829787.
  6. 1 2 3 4 Schankin, CJ, Maniyar, FH, Sprenger, T, Chou, DE, Eller, M, Goadsby, PJ, 2014, The Relation Between Migraine, Typical Migraine Aura and "Visual Snow", Headache, doi:10.1111/head.12378
  7. 1 2 3 4 5 Dodick, David; Silberstein, Stephen D. (2016). Migraine. Oxford University Press. p. 53. ISBN 9780199793617.
  8. 1 2 3 Schankin, C.; Maniyar, F.; Hoffmann, J.; Chou, D.; Goadsby, P. (22 April 2012). "Visual Snow: A New Disease Entity Distinct from Migraine Aura (S36.006)". Neurology. 78 (Meeting Abstracts 1): S36.006. doi:10.1212/WNL.78.1_MeetingAbstracts.S36.006.
  9. 1 2 3 Halpern, J (1 March 2003). "Hallucinogen persisting perception disorder: what do we know after 50 years?". Drug and Alcohol Dependence. 69 (2): 109–119. doi:10.1016/S0376-8716(02)00306-X. PMID 12609692.
  10. ↑ "Visual snow syndrome - About the Disease - Genetic and Rare Diseases Information Center". rarediseases.info.nih.gov. Retrieved 2022-10-30.
  11. ↑ Puledda, Francesca; Schankin, Christoph; Goadsby, Peter J. (2020-02-11). "Visual snow syndrome: A clinical and phenotypical description of 1,100 cases". Neurology. 94 (6): e564–e574. doi:10.1212/WNL.0000000000008909. ISSN 0028-3878. PMC 7136068. PMID 31941797.
  12. ↑ Schankin, CJ; Goadsby, PJ (June 2015). "Visual snow--persistent positive visual phenomenon distinct from migraine aura". Current Pain and Headache Reports. 19 (6): 23. doi:10.1007/s11916-015-0497-9. PMID 26021756. S2CID 6770765.
  13. 1 2 3 4 Puledda, Francesca; Schankin, Christoph; Goadsby, Peter (2020). "Visual snow syndrome. A clinical and phenotypical description of 1,100 cases" (PDF). Neurology. 94 (6): e564–e574. doi:10.1212/WNL.0000000000008909. PMC 7136068. PMID 31941797.
  14. ↑ Podoll K, Dahlem M, Greene S. Persistent migraine aura symptoms aka visual snow. (archived Feb 8, 2012)
  15. ↑ Schankin, Christoph J.; Maniyar, Farooq H.; Digre, Kathleen B.; Goadsby, Peter J. (2014-03-18). "'Visual snow' – a disorder distinct from persistent migraine aura". Brain. 137 (5): 1419–1428. doi:10.1093/brain/awu050. ISSN 1460-2156. PMID 24645145.
  16. ↑ "Headache Classification Committee of the International Headache Society (IHS) The International Classification of Headache Disorders, 3rd edition". Cephalalgia. 38 (1): 1–211. 2018-01-25. doi:10.1177/0333102417738202. ISSN 0333-1024. PMID 29368949.
  17. 1 2 Raghavan, Manoj; Remler, Bernd F.; Rozman1, Stephanie; Pelli, Denis G. (2010). "Patients with visual 'snow' have normal equivalent input noise levels" (PDF). Investigative Ophthalmology & Visual Science (51). Archived from the original (PDF) on 2016-04-11. Retrieved 2017-04-12.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  18. ↑ Dunn, FA; Rieke, F (August 2006). "The impact of photoreceptor noise on retinal gain controls". Current Opinion in Neurobiology. 16 (4): 363–70. doi:10.1016/j.conb.2006.06.013. PMID 16837189. S2CID 15543432.
  19. ↑ International Headache Society. The International Classification of Headache Disorders, 2nd edition" Cephalalgia 2004; 24 (suppl. 1): 1-160.
  20. ↑ "Headache". casemed.case.edu. Archived from the original on 2020-02-26. Retrieved 2019-11-04.
  21. ↑ Abraham HD (1983). "Visual phenomenology of the LSD flashback". Arch Gen Psychiatry. 40 (8): 884–889. doi:10.1001/archpsyc.1983.01790070074009. PMID 6135405.
  22. ↑ Schankin, Christoph; Goadsby, Peter (2015). "Visual Snow—Persistent Positive Visual Phenomenon Distinct from Migraine Aura" (PDF). Current Pain and Headache Reports. Uncommon and/or Unusual Headaches and Syndromes (6): 23. doi:10.1007/s11916-015-0497-9. PMID 26021756. S2CID 6770765.
  23. ↑ Puledda, Francesca; Goadsby, Peter (2021). "Localised increase in regional cerebral perfusion in patients with visual snow syndrome: a pseudo-continuous arterial spin labelling study" (PDF). Migraine. 92 (9): 918–926. doi:10.1136/jnnp-2020-325881. PMC 8372400. PMID 34261750.
  24. ↑ MIchels, Lars; Traber, Ghislaine (21 September 2021). "Widespread White Matter Alterations in Patients With Visual Snow Syndrome". Frontiers in Neurology. 12: 723805. doi:10.3389/fneur.2021.723805. PMC 8490630. PMID 34621237.
  25. ↑ "Neurofeedback in Visual Snow". ClinicalTrials.gov. U.S. National Library of Medicine. August 2021.
  26. ↑ "Transcranial Magnetic Stimulation For Visual Snow Syndrome (TMSVS)". ClinicalTrials.gov. U.S. National Library of Medicine. 7 June 2021.
  27. ↑ Puledda, Francesca; Vandenbussche, Nicolas; et al. (16 October 2021). "Evaluation of treatment response and symptom progression in 400 patients with visual snow syndrome". British Journal of Ophthalmology. 106 (9): 1318–1324. doi:10.1136/bjophthalmol-2020-318653. PMC 9411880. PMID 34656983. S2CID 239006203. Retrieved 3 February 2022.
  28. ↑ Grande, Marissa; Lattanzio, Lucas; Buard, Isabelle; McKendrick, Allison M.; Chan, Yu Man; Pelak, Victoria S. (2021). "A Study Protocol for an Open-Label Feasibility Treatment Trial of Visual Snow Syndrome with Transcranial Magnetic Stimulation". Frontiers in Neurology. 12: 724081. doi:10.3389/fneur.2021.724081. PMC 8500216. PMID 34630299.
  29. ↑ "VSI Update: Current & Ongoing Visual Snow Syndrome Research and Insights by Dr. Victoria Pelak". 5 September 2022.
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