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Visual snow is a transitory or persisting visual symptom where people see snow or television-like static in parts or the whole of their visual fields. According to the notion of hallucinatory form constants by Klüver (1942) and Siegel and Jarvik (1975), it can be conceived as a variety of visual hallucinations of random form dimension. As such, the phenomenon should not be confused with normal entoptic phenomena such as Haidinger's brush, which almost never have sufficient intensity to gain clinical significance as a source of suffering or functional impairment.

Contents 1 Causes 2 Related symptoms 3 Treatments 4 See also 5 External links 6 References

Visual snow, like all other forms of visual hallucinations, is non-specific as regards etiology (cause of illness). Therefore, each subject with a leading complaint of visual snow needs a full diagnostic work-up including ophthalmologic, neurological and psychiatric examinations as well as CAT or MRI scans of the brain.

Some find that they get Visual snow from being dehydrated or lack of Oxygen, for example if you are not very fit and you run a long distance, the runner may experience signs of visual snow from either being dehydrated or from lack of oxygen to the brain.

Visual snow can occur in a variety of ophthalmologic disorders that can be diagnosed by the presence of additional clinical signs and symptoms. Persisting visual snow can feature as a leading symptom of a migraine complication called persistent aura without infarction (International Headache Society, 2004), first described by Haas (1982) under the designation prolonged migraine aura status. It is important to keep in mind that there exist many clinical subforms of migraine where headache may be absent and where the migraine aura may not take the typical form of the zigzagged fortification spectrum, but manifests with a large variety of focal neurological symptoms, so that the condition is commonly under diagnosed.

Another frequent cause of visual snow is hallucinogen persisting perception disorder (HPPD) following use of LSD, MDMA (ecstasy), psychedelic mushrooms or other hallucinogens. In HPPD, the symptom of visual snow has been described by Abraham (1983) as aeropsia (literally "seeing the air"). It is noteworthy that HPPD can occur after a single dose of a hallucinogen and with a considerable latency between last drug intake and onset of persistent perception disorder, so taking a thorough life-time drug history is mandatory in the diagnostic-work up of visual snow. There exists anecdotal evidence from single case observations that a variety of other illegal or prescribed drugs including cannabis, antibiotics, anti-depressants and neuroleptics may cause visual snow or other symptoms of persisting perceptual disorder, but for the time being this has not been established for any of these aforementioned classes of drugs.

Moreover, a variety of illnesses (e.g. Lyme disease, auto-immune disease) or nocious events (e.g. prolonged use of a VDU, dehydration, over-acidification) have been blamed by sufferers in self-help internet forums as causes of persisting visual snow, but none of these claims have been supported by evidence-based medicine. Some patients fail to find any apparent causative illness or event in their lives, instead saying the snow came out of nowhere or has been with them for their whole life. It has been suggested by Jäger et al. (2005) that such cases of "primary persistent visual disturbance (visual snow phenomenon)" may possibly represent a variant phenotype of persistent aura without infarction.

In addition to visual snow, patients suffering from persistent perception disorder frequently have other types of visual disturbances such as starbursts, increased afterimages, floaters, trails, palinopsia and many others (Podoll et al., 2006). Non-visual symptoms such as tinnitus or depersonalisation-derealisation are also frequently encountered. All of these additional symptoms have been described as manifestations of both migraine aura and HPPD, emphasizing the major importance of these two diagnoses for an explanation of the visual snow condition. Patients suffering from visual snow may also percieve a stronger after image after looking at an object for merely a second. Secondary psychiatric sequelae such as anxiety, panic attacks or depression may develop and necessitate appropriate treatment.

There currently is no established treatment for visual snow. In HPPD, clonazepam has been recommended as medication of first choice in patients seeking medical help (Lerner et al., 2001). Furthermore, drug abstinence is of major therapeutic importance in HPPD. In persistent aura without infarction, the evidence so far suggests that acetazolamide may be the premier drug for patients with the repetitive form of aura status (Haan et al., 2000) and that valproate (Rothrock, 1997), lamotrigine (Chen et al., 2001), or topiramate (Podoll et al., 2005) should be first choices for patients with the continuous form. When these oral drugs are ineffective, an intravenous injection or injections of furosemide should be tried (Rozen, 2002). When part of ASD perceptual differences, carnosine may be used (Chez, 2002). However, with very little scientific research on the condition taking place, for the time being the effectiveness of such treatments remains based solely on anecdotal evidence. Beyond pharmacological approaches, appropriate counselling and cognitive behavioral interventions that focus on coping with the condition may be of huge importance.

• Eye
• Hallucinations
• Migraine
• Vision
• Asthenopia

• Support Forum For Visual Snow Patients
• Internet Resources For Visual Snow Patients
• Persistent aura without infarction
• Hallucinogen Persisting Perception Disorder

• Abraham HD. Visual phenomenology of the LSD flashback. Arch Gen Psychiatry 1983; 40: 884-889.
• Chen WT, Fuh JL, Lu SR, Wang SJ. Persistent migrainous visual phenomena might be responsive to lamotrigine. Headache 2001; 41: 823-825.
• Haan J, Sluis P, Sluis LH, Ferrari MD. Acetazolamide treatment for migraine aura status. Neurology 2000; 55: 1588-1589.
• Haas DC. Prolonged migraine aura status. Ann Neurol 1982; 11: 197-199.
• International Headache Society. The International Classification of Headache Disorders, 2nd edition. Cephalalgia 2004; 24 (suppl. 1): 1-160.
• Jäger HR, Giffin NJ, Goadsby PJ. Diffusion- and perfusion-weighted MR imaging in persistent migrainous visual disturbances. Cephalalgia 2005; 25: 323-332.
• Klüver H. Mechanisms of hallucinations. In: McNemar Q, Merrill MA (eds) Studies in personality. Contributed in honor of Lewis M. Terman. McGraw-Hill, New York-London 1942, 175-207.
• Lerner AG, Kladman I, Kodesh A, Sigal M, Shufman E. LSD-induced Hallucinogen Persisting Perception Disorder treated with clonazepam: two case reports. Isr J Psychiatry Relat Sci 2001; 38: 133-136.
• Podoll K, Dahlem M, Greene S. Persistent migraine aura symptoms aka visual snow. *Webpage from Migraine Aura Foundation website, 2006.
• Podoll K, Dahlem M, Haas DC. Persistent migraine aura without infarction - a detailed description. *Webpage from Migraine Aura Foundation website, 2005.
• Rothrock JF. Successful treatment of persistent migraine aura with divalproex sodium. Neurology 1997; 48: 261-262.
• Rozen TD. Treatment of a prolonged migrainous aura with intravenous furosemide. Neurology 2000; 55: 732-733.
• Siegel RK, Jarvik M. Drug-induced hallucinations in animals and man. In: Siegel R, West L (eds) Hallucinations: Behavior, experience, and theory. John Wiley and Sons, New York, NY 1975, 81-161.
• Michael G. Chez, MD. Carnosine Research. *Webpage from Autism Coach website, 2002.