|Visual snow syndrome|
|Other names||Persistent positive visual phenomenon, visual static, aeropsia|
|Animated example of visual snow-like noise|
|Symptoms||Static and auras in vision, Palinopsia, Blue field entoptic phenomenon, Nyctalopia, Tinnitus|
|Complications||Poor quality of vision, Photophobia, Heliophobia, Depersonalization and Derealization|
|Usual onset||Early to middle adulthood|
|Causes||Unknown, anxiety, hyperexcitability of neurons and processing problems in the visual cortex|
|Risk factors||Migraine sufferer|
|Differential diagnosis||Migraine aura, Persistent aura without infarction, Hallucinogen persisting perception disorder|
|Medication||Anticonvulsants (limited evidence and success)|
Visual snow, also known as visual static, is an uncommon neurological condition in which the affected individuals see white or black dots or transparent dots in part or the whole of their visual fields. The condition is typically always present and can last years. Migraine and tinnitus are common comorbidities and are both associated with a more severe presentation of the syndrome.
The cause of visual snow is unclear. The underlying mechanism is believed to involve excessive excitability of neurons in the right lingual gyrus and left cerebellar anterior lobe of the brain. Research has been limited because of 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. Medications that may be used to treat the condition include lamotrigine, acetazolamide, or verapamil. However, these do not commonly result in benefits and the evidence for their use is very limited.
Signs and symptoms
People report seeing "snow", much like the visual noise or "static" on a TV screen after transmission ends. In addition to this visual snow, many of those affected have other types of visual disturbances such as starbursts, increased afterimages, floaters, trails, and many others.
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.
- Visual snow: dynamic, continuous, tiny dots in the entire visual field lasting 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 (phosphenes), 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, drug abuse).
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.
Patients with visual "snow" have normal equivalent input noise levels and contrast sensitivity. In a 2010 study, Raghaven et al. hypothesize that what the patients see as "snow" is eigengrau. 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".
The causes are unclear. The underlying mechanism is believed to involve excessive excitability of neurons within the cortex of the brain, specifically the right lingual gyrus and left cerebellar anterior lobe of the brain.
Persisting visual snow can feature as a leading addition to a migraine complication called persistent aura without infarction, 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.
Visual snow does not depend on the effect of psychotropic substances on the brain. Hallucinogen persisting perception disorder (HPPD), a condition caused by hallucinogenic drug use, is sometimes linked to visual snow, but both the connection of visual snow to HPPD and the cause and prevalence of HPPD is disputed. Most of the evidence for both is generally anecdotal, and subject to spotlight fallacy.
- In September 2021, two studies found white matter alterations in parts of the visual cortex and outside the visual cortex in patients with visual snow syndrome.
- In June 2021, University of Colorado researchers started recruiting for a clinical trial on transcranial magnetic stimulation for visual snow syndrome.
- In May 2021, University of Zurich researchers announced a clinical trial on neurofeedback for visual snow syndrome.
- In December 2020, a study found local increases in regional cerebral perfusion in patients with visual snow syndrome.
- In May 2015, visual snow was described as a persisting positive visual phenomenon distinct from migraine aura in a study by Schankin and Goadsby.
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. Medications that may be used include lamotrigine, acetazolamide, or verapamil, but these do not always result in benefits. As of 2021, there are two ongoing clinical trials using transcranial magnetic stimulation and neurofeedback for visual snow.
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- MIchels, Lars; Ghislaine, Traber (21 September 2021). "Widespread White Matter Alterations in Patients With Visual Snow Syndrome". Frontiers in Neurology. doi:10.3389/fneur.2021.723805.
- Puledda, Francesca; Goadsby, Peter. "Localised increase in regional cerebral perfusion in patients with visual snow syndrome: a pseudo-continuous arterial spin labelling study" (PDF). Migraine. doi:10.1136/jnnp-2020-325881. PMC 8372400.
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- "Neurofeedback in Visual Snow". ClinicalTrials.gov. U.S. National Library of Medicine.
- "Transcranial Magnetic Stimulation For Visual Snow Syndrome (TMSVS)". ClinicalTrials.gov. U.S. National Library of Medicine.
- Visual Snow Initiative
- Visual snow syndrome at NIH
- Eye On Vision Foundation