Editing Visual snow syndrome

{{Redirect|Visual snow|the display of noise in an analog video signal|Noise (video)|the related phenomenon known as seeing stars|Phosphene}}
{{short description|Visual impairment}}
{{Infobox medical condition
| name = Visual snow syndrome
| synonyms = Persistent positive visual phenomenon,<ref name="LarkinCommunityHospital">{{cite journal|first1=Joseph|last1=Licht|first2=Kathryn|last2=Ireland|first3=Matthew|last3=Kay|title=Visual Snow: Clinical Correlations and Workup A Case Series|url=https://www.researchgate.net/publication/303300977|website=researchgate.net|date=2016 |publisher=Larkin Community Hospital|access-date=3 September 2017|doi=10.13140/RG.2.1.2393.9443}}</ref> visual static, aeropsia
| image = File:Illustration of visual snow.jpg
| image_size = 250
| alt = refer to caption
| caption = Illustration of visual snow
| pronounce = 
| synonym = 
| field = [[Neurology]], [[Neuro-ophthalmology]]
| symptoms = [[Noise (video)|Static]] and [[Visual aura|auras]] in vision, [[Palinopsia]], [[Blue field entoptic phenomenon]], [[Nyctalopia]], [[Tinnitus]]
| complications = Poor quality of vision, [[Photophobia]], [[Heliophobia]], [[Depersonalization]] and [[Derealization]]<ref name=Depersonalization>{{Cite web|url=https://www.visualsnowinitiative.org/diagnostic-criteria/|title=Diagnostic Criteria &#124; Visual Snow Initiative|date=23 March 2023 }}</ref>
| onset = Visual Snow can appear at any time, but it commonly appears at birth, late teenage years, and early adulthood.
| duration = 
| types = 
| causes = Unknown,<ref name=Bro2016>{{cite book|last1=Brodsky|first1=Michael C.|title=Pediatric Neuro-Ophthalmology|date=2016|publisher=Springer|isbn=9781493933846|page=285|url=https://books.google.com/books?id=f_mODAAAQBAJ&pg=PA285|language=en}}</ref> hyperexcitability of [[neurons]] and processing problems in the [[visual cortex]]<ref name=Bou2017/><ref>{{Cite journal|url=https://pubmed.ncbi.nlm.nih.gov/28349350/|pmid = 28349350|year = 2017|last1 = Bou Ghannam|first1 = A.|last2 = Pelak|first2 = V. S.|title = Visual Snow: A Potential Cortical Hyperexcitability Syndrome|journal = Current Treatment Options in Neurology|volume = 19|issue = 3|page = 9|doi = 10.1007/s11940-017-0448-3|s2cid = 4829787}}</ref>
| risks = [[Migraine]] sufferer,<ref name=VSHEADACHE2014 /> [[Psychoactive drug|psychoactive substance use]]
| diagnosis = 
| differential = [[Scintillating scotoma|Migraine aura]],<ref name=Ox2016/> [[Persistent aura without infarction]], [[Hallucinogen persisting perception disorder]]<ref name="ReferenceA" /><ref name="ReferenceB" />
| prevention = 
| treatment = 
| medication = [[Anticonvulsants]]<ref name="Ox2016" /><ref name=Bro2016/> (limited evidence and success)
| frequency = Uncommon (understudied)
| deaths = 
}}

<!-- Definition and symptoms -->
'''Visual snow syndrome''' ('''VSS''') is an uncommon [[neurological]] condition in which the primary symptom is visual snow, a persistent flickering [[noise (video)|white, black, transparent, or colored dots]] across the whole [[visual field]].<ref name="Ox2016">{{cite book|last1=Dodick|first1=David|last2=Silberstein|first2=Stephen D.|title=Migraine|date=2016|publisher=Oxford University Press|isbn=9780199793617|page=53|url=https://books.google.com/books?id=Y-wmDAAAQBAJ&pg=PA53|language=en}}</ref><ref name="Bou2017">{{cite journal|last1=Bou Ghannam|first1=A|last2=Pelak|first2=VS|title=Visual snow: a potential cortical hyperexcitability syndrome|journal=Current Treatment Options in Neurology|date=March 2017|volume=19|issue=3|pages=9|doi=10.1007/s11940-017-0448-3|pmid=28349350|s2cid=4829787}}</ref> It is distinct from the ''symptom'' of visual snow itself, which can also be caused by several other causes; these cases are referred to as "VSS mimics."<ref name=":0">{{Cite journal |last1=Hang |first1=Chenyue |last2=Leishangthem |first2=Lakshmi |last3=Yan |first3=Yan |date=2021 |title=Not All Cases of Visual Snows are Benign: Mimics of Visual Snow Syndrome |journal=Neuropsychiatric Disease and Treatment |volume=17 |pages=3293–3300 |doi=10.2147/NDT.S338111 |doi-access=free |issn=1176-6328 |pmc=8591117 |pmid=34785899}}</ref> Other names for the syndrome include "'''scotopic sensitivity syndrome'''", "'''Meares-Irlen syndrome'''", and "'''asfedia'''."<ref>{{Cite web |title=Visual Snow |url=https://eyewiki.org/Visual_Snow |website=EyeWiki |publisher=[[American Academy of Ophthalmology]]}}</ref>

Other common symptoms are [[palinopsia]], enhanced [[Entoptic phenomenon|entoptic phenomena]], [[photophobia]], and [[Headache|tension headaches]].<ref name=":1">{{Cite web |title=Visual snow syndrome - About the Disease - Genetic and Rare Diseases Information Center |url=https://rarediseases.info.nih.gov/diseases/12062/visual-snow-syndrome |access-date=2022-10-30 |website=rarediseases.info.nih.gov |language=en}}</ref><ref>{{Cite journal |last1=Puledda |first1=Francesca |last2=Schankin |first2=Christoph |last3=Goadsby |first3=Peter J. |date=2020-02-11 |title=Visual snow syndrome: A clinical and phenotypical description of 1,100 cases |journal=Neurology |language=en |volume=94 |issue=6 |pages=e564–e574 |doi=10.1212/WNL.0000000000008909 |issn=0028-3878 |pmid=31941797|pmc=7136068 }}</ref> The condition is typically always present and has no known cure, as viable treatments are still under research.<ref>{{cite journal|last1=Schankin|first1=CJ|last2=Goadsby|first2=PJ|title=Visual snow--persistent positive visual phenomenon distinct from migraine aura|journal=Current Pain and Headache Reports|date=June 2015|volume=19|issue=6|pages=23|doi=10.1007/s11916-015-0497-9|pmid=26021756|s2cid=6770765}}</ref> [[Astigmatism]], although not presumed connected to these visual disturbances, is a common comorbidity. [[Migraine]]s and [[tinnitus]] are common comorbidities that are both associated with a more severe presentation of the syndrome.<ref name="Puledda20">{{cite journal |last1=Puledda |first1=Francesca |last2=Schankin |first2=Christoph |last3=Goadsby |first3=Peter |title=Visual snow syndrome. A clinical and phenotypical description of 1,100 cases. |journal=Neurology |date=2020 |volume=94 |issue=6 |pages=e564–e574 |doi=10.1212/WNL.0000000000008909 |pmid=31941797 |pmc=7136068 |url=https://n.neurology.org/content/neurology/94/6/e564.full.pdf}}</ref> <!-- Cause and diagnosis -->

The cause of the syndrome is unclear.<ref name="Bro2016">{{cite book|last1=Brodsky|first1=Michael C.|title=Pediatric Neuro-Ophthalmology|date=2016|publisher=Springer|isbn=9781493933846|page=285|url=https://books.google.com/books?id=f_mODAAAQBAJ&pg=PA285|language=en}}</ref> The underlying mechanism is believed to involve excessive excitability of neurons in the right [[lingual gyrus]] and left [[anterior lobe of cerebellum|anterior lobe of the 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 the inability to suppress excitatory sensory information.<ref name="Bou2017" /><ref name="VSHEADACHE2014" /> Research has been limited due to issues of case identification, diagnosis, and the limited size of any studied cohort, though the issue of diagnosis is now largely addressed. Initial functional brain imaging research suggests visual snow is a [[brain disorder]].<ref>{{Cite journal |last2= Piccirelli|first2= Marco|last3= Michels|first3= Lars|date=February 2, 2020 |title=Visual snow syndrome: a review on diagnosis, pathophysiology, and treatment |url=https://journals.lww.com/10.1097/WCO.0000000000000768 |journal=Current Opinion in Neurology |language=en |volume=33 |issue=1 |pages=74–78 |doi=10.1097/WCO.0000000000000768 |issn=1350-7540 |via=NHI|last1= Traber|first1= Ghislaine L.|pmid= 31714263|url-access=subscription }}</ref>

== Difference from visual snow ==
Visual snow – the symptom – may sometimes be a transient experience, and it is possible that it is a natural phenomenon, sometimes thought to be visible to many people if they focus on it.<ref name=":3">{{Cite journal |last1=Costa |first1=Rui Miguel |last2=Campos |first2=Pedro |last3=Wiborg |first3=Madalena |last4=Rebôlo |first4=Catarina |last5=Wittmann |first5=Marc |last6=Kornmeier |first6=Jürgen |date=2022 |title=Prevalence of visual snow and relation to attentional absorption |journal=PLOS ONE |volume=17 |issue=11 |pages=e0276971 |doi=10.1371/journal.pone.0276971 |doi-access=free |issn=1932-6203 |pmc=9639836 |pmid=36342911|bibcode=2022PLoSO..1776971C }}</ref> In visual snow syndrome, however, visual snow is ever-present, regardless of lighting conditions and even when the eyes are closed.<ref name=":4">{{Cite journal |last1=Sampatakakis |first1=Stefanos N. |last2=Lymperopoulos |first2=Loukas |last3=Mavridis |first3=Theodoros |last4=Karagiorgis |first4=Georgios |last5=Papadopoulos |first5=Constantinos |last6=Deligianni |first6=Christina I. |last7=Mitsikostas |first7=Dimos D. |date=November 2022 |title=Visual snow: A systematic review and a case series |url=https://pubmed.ncbi.nlm.nih.gov/35945691 |journal=Cephalalgia: An International Journal of Headache |volume=42 |issue=13 |pages=1409–1419 |doi=10.1177/03331024221118917 |issn=1468-2982 |pmid=35945691}}</ref> In contrast to visual phenomena caused by migraines, which can last up to about an hour, static caused by visual snow syndrome lasts continuously for several months.<ref name=":4" />

If visual snow is persistent, continuous, and accompanied by other symptoms, such as [[entoptic phenomenon]], [[palinopsia]], [[photophobia]] and/or [[nyctalopia]] – it may indicate visual snow syndrome.<ref name=":4" /> This syndrome is not just a phenomenon, but a [[neurological condition]],<ref name=":4" /> where a person experiences constant visual disturbances, regardless of lighting conditions.<ref name=":4" /> Visual snow syndrome is be linked to heightened neural sensitivity in the visual regions of the brain.<ref>{{Cite journal |last1=Klein |first1=Antonia |last2=Schankin |first2=Christoph J. |date=October 2021 |title=Visual snow syndrome, the spectrum of perceptual disorders, and migraine as a common risk factor: A narrative review |journal=Headache |volume=61 |issue=9 |pages=1306–1313 |doi=10.1111/head.14213 |issn=1526-4610 |pmc=9293285 |pmid=34570907}}</ref> However, it is important not to confuse it with other causes of visual snow, sometimes referred to as VSS mimics.<ref name=":0" />

== Signs and symptoms ==
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 visual symptoms.<ref name="Puledda20" />

Non-visual symptoms may include difficulty concentrating, insomnia, frequent migraines, nausea, and vertigo. <ref>Cleveland Clinic. (2024). ''Visual Snow Syndrome.'' https://my.clevelandclinic.org/health/diseases/24444-visual-snow-syndrome.</ref>

===Diagnosis===

Visual snow syndrome is usually diagnosed with the following proposed criteria:<ref>{{Cite journal|last1=Schankin|first1=Christoph J.|last2=Maniyar|first2=Farooq H.|last3=Digre|first3=Kathleen B.|last4=Goadsby|first4=Peter J.|date=2014-03-18|title='Visual snow' – a disorder distinct from persistent migraine aura|journal=Brain|language=en|volume=137|issue=5|pages=1419–1428|doi=10.1093/brain/awu050|pmid=24645145|issn=1460-2156|doi-access=free}}</ref><ref>{{Cite journal|date=2018-01-25|title=Headache Classification Committee of the International Headache Society (IHS) The International Classification of Headache Disorders, 3rd edition|journal=Cephalalgia|language=en|publication-date=2018-01-25|volume=38|issue=1|pages=1–211|doi=10.1177/0333102417738202|pmid=29368949|issn=0333-1024|doi-access=free}}</ref><ref name="Puledda20" />

* 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:
** i. [[Palinopsia]]. At least 1 of the following: afterimages or trailing of moving objects.
** ii. Enhanced [[entoptic phenomena]]. At least 1 of the following: excessive [[floaters]] in both eyes, excessive [[blue field entoptic phenomenon]], self-light of the eye ([[phosphene]]s), or spontaneous [[photopsia]].
** iii. [[Photophobia]].
** iv. [[Nyctalopia]]; impaired night vision.
* Symptoms are not consistent with typical [[migraine aura]].
* Symptoms are not better explained by another disorder ([[ophthalmological]], [[Substance abuse|drug abuse]]).
** Normal ophthalmology tests (best-corrected [[visual acuity]], [[dilated fundus examination]], visual field, and [[electroretinogram]]); not caused by previous intake of [[psychotropic]] drugs.

Additional and non-visual symptoms like [[tinnitus]], ear pressure, [[brain fog]], and more might be present. It can also be diagnosed by [[PET scan]].{{Citation needed|date=April 2025}}

==== Mimics ====
The following conditions other than visual snow syndrome can also cause visual snow symptoms, and care must be taken not to confuse them with it:<ref name=":2">{{Cite journal |last1=Hang |first1=Chenyue |last2=Leishangthem |first2=Lakshmi |last3=Yan |first3=Yan |date=2021 |title=Not All Cases of Visual Snows are Benign: Mimics of Visual Snow Syndrome |journal=Neuropsychiatric Disease and Treatment |volume=17 |pages=3293–3300 |doi=10.2147/NDT.S338111 |doi-access=free |issn=1176-6328 |pmc=8591117 |pmid=34785899}}</ref>

* Neurological conditions affecting the [[Occipital lobe|occipital visual area]], e.g. stroke, epilepsy, multiple sclerosis<ref name=":2" />
* [[Occipital epilepsy]]<ref name=":2" />
* Occipital stroke<ref name=":2" />
* "Heidenhain variants" of [[sporadic Creutzfeldt–Jakob disease]], a fatal [[prion disease]], possibly due to its effects on the occipital cortex<ref name=":2" />
* Glycine receptor antibody syndrome, possibly because [[Glycine receptor, alpha 1|Glycine receptor alpha-1 subunit]] is an [[inhibitory neurotransmitter]] of the human retina<ref name=":2" />
* [[Head injury|Head trauma]], possibly indicating injury to visual areas<ref name=":2" />
* Ocular abnormalities, e.g. [[macular atrophy]], [[central serous retinopathy]]<ref name=":2" />
* Retinal disease, including [[rod-cone dystrophy]] or [[retinitis pigmentosa]]<ref name=":2" />
* [[Uveitis]]<ref name=":2" />
* [[Hallucinogen persisting perception disorder]], possibly because both it and VSS involve changes in serotonergic [[synaptic transmission]]<ref name=":2" />
* Drug-related visual snow, which can be caused by several medications<ref name=":2" />
* Other systemic diseases not listed here<ref name=":2" />

It must also be distinguished from [[Migraine with aura|migraine with visual aura]].<ref name=":2" />

=== Common misconceptions ===

* 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. Additionally, psychological disorders, such as [[Somatic symptom disorder|somatic disorders]], could potentially contribute to these perceptual disturbances.<ref>{{Cite journal |date=October 6, 2013 |title= Origin and effect of phototransduction noise in primate cone photoreceptors|journal= Nature Neuroscience|pmc=3815624 |last1=Angueyra |first1=J. M. |last2=Rieke |first2=F. |volume=16 |issue=11 |pages=1692–1700 |doi=10.1038/nn.3534 |pmid=24097042 }}</ref><ref>{{Cite journal |date=November 4, 2022 |title=Recent developments on psychological factors in medically unexplained symptoms and somatoform disorders |journal= Frontiers in Public Health|pmc=9672811 |last1=Mewes |first1=R. |volume=10 |doi=10.3389/fpubh.2022.1033203 |doi-access=free |pmid=36408051 }}</ref>
* '''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 related to how the eyes and brain process visual information in low-light conditions. In such environments, the visual system becomes more sensitive to light, amplifying noise or minor changes in visual signals. For example, in low-light conditions, rod photoreceptors, responsible for light perception in dim environments, are primarily activated. However, they cannot distinguish details or colors, leading to a blurred and grainy visual experience without clear contours. Cones, responsible for color perception and detail, are activated in brighter light, while rods provide vision in low-light conditions but with reduced precision. Therefore, the graininess perceived in the dark is a natural adaptation of our vision to photoreceptor limitations, not an indication of abnormality. It's important to note that the perception of such phenomena may vary among individuals due to differences in perception and sensitivity.<ref>{{Cite journal |last1=Sweeny |first1=Timothy D. |last2=Grabowecky |first2=Marcia |last3=Paller |first3=Ken A. |last4=Suzuki |first4=Satoru |date=2008-05-01 |title=Random and systematic effects of neural noise on low-level and high-level pattern vision |url=https://jov.arvojournals.org/article.aspx?articleid=2137308 |journal=Journal of Vision |volume=8 |issue=6 |pages=593 |doi=10.1167/8.6.593 |issn=1534-7362|doi-access=free }}</ref><ref>{{Cite journal |last1=Li |first1=Yanfeng |last2=Luo |first2=Yongbiao |last3=Zheng |first3=Yingjian |last4=Liu |first4=Guiqian |last5=Gong |first5=Jiekai |date=2024-10-21 |title=Research on Target Image Classification in Low-Light Night Vision |journal=Entropy (Basel, Switzerland) |volume=26 |issue=10 |pages=882 |doi=10.3390/e26100882 |doi-access=free |issn=1099-4300 |pmc=11507526 |pmid=39451958|bibcode=2024Entrp..26..882L }}</ref><ref>{{Cite journal |last=Ala-Laurila |first=Petri |date=2025-01-21 |title=Visual pigments underlie the sensitivity difference between day and night vision |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=122 |issue=3 |pages=e2424071122 |doi=10.1073/pnas.2424071122 |issn=1091-6490 |pmc=11761961 |pmid=39805024|bibcode=2025PNAS..12224071A }}</ref>
* [[Closed-eye hallucination|Visual noise with closed eyes]], also known as phosphenes, refers to the phenomenon where a person perceives random light or dark spots without an external light source. This effect is linked to the ongoing activity of the visual system, even with closed eyes, and can be caused by the electrical activity of neurons in the retina or visual cortex. Studies have shown that the visual system becomes more sensitive when the eyes are closed, which may lead to the perception of phosphenes or visual noise in the dark. These phenomena are a normal part of brain function as it continues processing information in the absence of external stimuli <ref>{{Cite journal |last1=de Graaf |first1=T. A. |last2=Duecker |first2=F. |last3=Stankevich |first3=Y. |last4=Ten Oever |first4=S. |last5=Sack |first5=A. T. |date=2017 |title=Seeing in the dark: Phosphene thresholds with eyes open versus closed in the absence of visual inputs |url=https://pubmed.ncbi.nlm.nih.gov/28522346 |journal=Brain Stimulation |volume=10 |issue=4 |pages=828–835 |doi=10.1016/j.brs.2017.04.127 |issn=1876-4754 |pmid=28522346|hdl=21.11116/0000-0006-08F8-A |hdl-access=free }}</ref><ref>{{Cite journal |last=Schwiedrzik |first=Caspar M. |date=2009 |title=Retina or visual cortex? The site of phosphene induction by transcranial alternating current stimulation |journal=Frontiers in Integrative Neuroscience |volume=3 |pages=6 |doi=10.3389/neuro.07.006.2009 |doi-access=free |issn=1662-5145 |pmc=2691656 |pmid=19506706}}</ref>

===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.<ref name=VSHEADACHE2014 />

Non-visual symptoms of visual snow can include [[depersonalization]], [[derealization]], [[Depression (mood)|depression]], [[photophobia]], and [[heliophobia]] in the individual affected.<ref name=Depersonalization />

Patients with visual "snow" have normal equivalent input noise levels and [[contrast sensitivity]].<ref name="Pelli" /> In a 2010 study, Raghaven et al. hypothesize that what the patients see as "snow" is [[eigengrau]].<ref name="Pelli">{{cite journal|first1=Manoj|last1=Raghavan|first2=Bernd F.|last2=Remler|first3=Stephanie|last3=Rozman1|first4=Denis G.|last4=Pelli|title=Patients with visual 'snow' have normal equivalent input noise levels|date=2010|journal=Investigative Ophthalmology & Visual Science|issue=51|url=https://psych.nyu.edu/pelli/pubs/raghavan2010arvo-snow.pdf|access-date=2017-04-12|archive-date=2016-04-11|archive-url=https://web.archive.org/web/20160411083446/http://psych.nyu.edu/pelli/pubs/raghavan2010arvo-snow.pdf|url-status=dead}}</ref> 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".<ref>{{cite journal|last1=Dunn|first1=FA|last2=Rieke|first2=F|title=The impact of photoreceptor noise on retinal gain controls|journal=Current Opinion in Neurobiology|date=August 2006|volume=16|issue=4|pages=363–70|doi=10.1016/j.conb.2006.06.013|pmid=16837189|s2cid=15543432}}</ref><ref>{{Cite journal |date=November 2, 2015 |title=Chromatic detection from cone photoreceptors to V1 neurons to behavior in rhesus monkeys |journal=  Journal of Vision|pmc=4633035 |last1=Hass |first1=C. A. |last2=Angueyra |first2=J. M. |last3=Lindbloom-Brown |first3=Z. |last4=Rieke |first4=F. |last5=Horwitz |first5=G. D. |volume=15 |issue=15 |page=1 |doi=10.1167/15.15.1 |pmid=26523737 }}</ref>

==Causes==
The causes of VSS are not clear.<ref name=Bro2016/> The underlying mechanism is believed to involve excessive excitability of neurons within the [[Cortex (anatomy)|cortex]] of the [[brain]],<ref name=Bou2017/> specifically the right [[lingual gyrus]] and left [[cerebellar]] [[Anterior lobe of cerebellum|anterior lobe]] of the brain.<ref name="VSHEADACHE2014">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}}</ref>

Persisting visual snow can feature as a leading addition to a [[migraine]] complication called [[persistent aura without infarction]],<ref>International Headache Society. The International Classification of Headache Disorders, 2nd edition" ''Cephalalgia'' 2004; 24 (suppl. 1): 1-160.</ref> 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.<ref>{{Cite web|url=http://casemed.case.edu/clerkships/neurology/NeurLrngObjectives/Headache.htm|title=Headache|website=casemed.case.edu|access-date=2019-11-04|archive-date=2020-02-26|archive-url=https://web.archive.org/web/20200226013125/http://casemed.case.edu/clerkships/neurology/NeurLrngObjectives/Headache.htm|url-status=dead}}</ref>

Visual snow does not depend on the effect of [[psychotropic]] substances on the brain.<ref name="Puledda20"/> [[Hallucinogen persisting perception disorder]] (HPPD), a condition caused by hallucinogenic drug use, is sometimes linked to visual snow,<ref>{{cite journal | author = Abraham HD | year = 1983 | title = Visual phenomenology of the LSD flashback | journal = Arch Gen Psychiatry | volume = 40 | issue = 8| pages = 884–889 | doi=10.1001/archpsyc.1983.01790070074009| pmid = 6135405 }}</ref> but both the connection of visual snow to HPPD<ref name="ReferenceA">{{cite journal|last1=Schankin|first1=C.|last2=Maniyar|first2=F.|last3=Hoffmann|first3=J.|last4=Chou|first4=D.|last5=Goadsby|first5=P.|title=Visual Snow: A New Disease Entity Distinct from Migraine Aura (S36.006)|journal=Neurology|date=22 April 2012|volume=78|issue=Meeting Abstracts 1|pages=S36.006|doi=10.1212/WNL.78.1_MeetingAbstracts.S36.006}}</ref> and the cause and prevalence of HPPD are disputed.<ref name="ReferenceB">{{cite journal|last1=Halpern|first1=J|title=Hallucinogen persisting perception disorder: what do we know after 50 years?|journal=Drug and Alcohol Dependence|date=1 March 2003|volume=69|issue=2|pages=109–119|doi=10.1016/S0376-8716(02)00306-X|pmid=12609692}}</ref> Most of the evidence for both is generally anecdotal and subject to [[spotlight fallacy]].<ref name="ReferenceA"/><ref name="ReferenceB"/> Visual snow has also been correlated with head trauma and infection.<ref>{{Cite journal |last2= Leishangthem|first2= Lakshmi|last3= Yan|first3= Yan|date=November 10, 2021 |title=Not All Cases of Visual Snows are Benign: Mimics of Visual Snow Syndrome |journal=Neuropsychiatric Disease and Treatment |language=en |volume=17 |pages=3293–3300 |doi= 10.2147/NDT.S338111|doi-access= free|issn=1178-2021 |pmc=8591117 |pmid= 34785899|last1= Hang|first1= Chenyue}}</ref>

==Timeline==
* In May 2015, visual snow was described as a persisting positive visual phenomenon distinct from migraine aura in a study by Schankin and [[Peter Goadsby|Goadsby]].<ref>{{cite journal |last1=Schankin |first1=Christoph |last2=Goadsby |first2=Peter |title=Visual Snow—Persistent Positive Visual Phenomenon Distinct from Migraine Aura |journal=Current Pain and Headache Reports |year=2015 |volume=Uncommon and/or Unusual Headaches and Syndromes |issue=6 |page=23 |doi=10.1007/s11916-015-0497-9 |pmid=26021756 |s2cid=6770765 |url=https://link.springer.com/content/pdf/10.1007/s11916-015-0497-9.pdf}}</ref>
* In December 2020, a study<ref>{{cite journal |last1=Puledda |first1=Francesca |last2=Goadsby |first2=Peter |title=Localised increase in regional cerebral perfusion in patients with visual snow syndrome: a pseudo-continuous arterial spin labelling study |journal=Migraine |year=2021 |volume=92 |issue=9 |pages=918–926 |doi=10.1136/jnnp-2020-325881 |pmid=34261750 |url=https://jnnp.bmj.com/content/jnnp/92/9/918.full.pdf|pmc=8372400 }}</ref> found local increases in regional cerebral perfusion in patients with visual snow syndrome.
* In September 2021, two studies<ref>{{cite journal |last1=MIchels |first1=Lars |last2=Traber |first2=Ghislaine |title=Widespread White Matter Alterations in Patients With Visual Snow Syndrome |journal=Frontiers in Neurology |date=21 September 2021 |volume=12 |page=723805 |doi=10.3389/fneur.2021.723805|pmid=34621237 |pmc=8490630 |doi-access=free }}</ref> found [[white matter]] alterations in parts of the visual cortex and outside the visual cortex in patients with visual snow syndrome.
* In November 2023, a study<ref>Puledda, F., Dipasquale, O., Gooddy, B. J., Karsan, N., Bose, R., Mehta, M. A., Williams, S., & Goadsby, P. (2023). Abnormal Glutamatergic and Serotonergic Connectivity in Visual Snow Syndrome and Migraine with Aura. Annals of Neurology, 94(5), 873–884. https://doi.org/10.1002/ana.26745</ref> revealed that glutamate and serotonin are involved in brain connectivity alterations in areas of the visual, salience, and [[limbic system]]s in VSS. Importantly, altered serotonergic connectivity is independent of migraine in VSS, and simultaneously comparable to that of migraine with aura, highlighting a shared biology between the disorders.<ref>{{Cite journal |date=December 2, 2014 |title=Coincidence Detection of Single-Photon Responses in the Inner Retina at the Sensitivity Limit of Vision |url=https://www.researchgate.net/publication/268526375 |journal= Current Biology|bibcode=2014CBio...24.2888A |last1=Ala-Laurila |first1=Petri |last2=Rieke |first2=Fred |volume=24 |issue=24 |pages=2888–2898 |doi=10.1016/j.cub.2014.10.028 |pmid=25454583 |pmc=4269560 }}</ref>

==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.<ref name=Bou2017/> In some studies, lamotrigine as a treatment for visual snow syndrome only showed efficacy in 20% of patients, and in one study, patients using lamotrigine even reported worsening symptoms.<ref>{{Cite journal |last2= Puledda|first2= Francesca|date=August 8, 2023 |title=Visual snow syndrome and migraine: a review |journal=Eye |language=en |volume=37 |issue=12 |pages=2374–2378 |doi=10.1038/s41433-023-02435-w |issn=1476-5454|pmc=10397188 |last1= Silva|first1= Elisa Martins|pmid= 36788360}}</ref> Medications that may be used include [[lamotrigine]], [[acetazolamide]], [[verapamil]],<ref name=Bou2017/> [[clonazepam]], [[propranolol]], and [[sertraline]]<ref>{{Cite book |last1=Gomides |first1=Dr. Mariuche |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/S0079612320300625 |title=Update on Emerging Treatments for Migraine |last2=Starling-Alves |first2=Isabela |last3=H. Santos |first3=Dr Flavia |chapter=Chapter 11 - Insights into pathophysiology and treatment of visual snow syndrome: A systematic review |series=Progress on Brain Research |volume=255 |pages=311–326 |publisher=Elsevier |doi=10.1016/bs.pbr.2020.05.020 |pmid=33008511 |isbn=978-0443223105 |s2cid=222146213 |publication-date=2023-12-06}}</ref> but these do not always result in positive effects.<ref name="Ox2016" /><ref name=Bro2016/> As of 2021, two ongoing clinical trials were using [[transcranial magnetic stimulation]] and [[neurofeedback]] for visual snow.<ref>{{cite journal |title=Neurofeedback in Visual Snow |url=https://clinicaltrials.gov/ct2/show/NCT04902365 |website=ClinicalTrials.gov |date=August 2021 |publisher=U.S. National Library of Medicine}}</ref><ref>{{cite journal |title=Transcranial Magnetic Stimulation For Visual Snow Syndrome (TMSVS) |url=https://clinicaltrials.gov/ct2/show/NCT04925232 |website=ClinicalTrials.gov |date=7 June 2021 |publisher=U.S. National Library of Medicine}}</ref>

A recent study in the ''[[British Journal of Ophthalmology]]'' has confirmed that common drug treatments are generally ineffective in visual snow syndrome (VSS). [[Vitamin]]s and [[benzodiazepine]]s, however, were shown to be beneficial in some patients and can be considered safe for this condition.<ref>{{cite journal |last1=Puledda |first1=Francesca |last2=Vandenbussche |first2=Nicolas |last3=Moreno-Ajona |first3=David |last4=Eren |first4=Ozan |last5=Schankin |first5=Christoph |last6=Goadsby |first6=Peter J |display-authors = 2 |title=Evaluation of treatment response and symptom progression in 400 patients with visual snow syndrome |journal=British Journal of Ophthalmology |date=16 October 2021 |volume=106 |issue=9 |pages=1318–1324 |doi=10.1136/bjophthalmol-2020-318653 |pmid=34656983 |pmc=9411880 |s2cid=239006203 }}</ref>

==References==
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{{Visual phenomena}}

[[Category:Visual disturbances and blindness]]
[[Category:Hallucinations]]
[[Category:Syndromes of unknown causes]]
[[Category:Medical controversies]]
[[Category:Migraine]]