Visual Snow Syndrome

Imagine an old-school television that receives no (or a very weak) transmission signal. You will hear white noise and you will see a sort of random snow pattern or static.

Your brain may also be having 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, even with the eyes closed. The dots remain individual and do not clump together or change in size. 

This syndrome is called Visual Snow Syndrome. It is uncommon neurological condition with an unknown etiology[1]. The condition is typically always present and has no known cure. Visual snow symptoms commonly appear during the late teenage years and early adulthood. Migraine and tinnitus are common comorbidities and are both associated with a more severe presentation of the syndrome.

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.

The underlying mechanism is believed to involve excessive excitability of neurons in some parts of the brain. Research has been limited due to issues of case identification and diagnosis, 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 (normally used to treat focal epilepsy), acetazolamide (normally used to treat epilepsy) or verapamil (normally used for the prevention of migraines and cluster headaches). However, these do not commonly result in benefits and the evidence for their use is very limited.

[1] Puledda et al: Visual snow syndrome: A clinical and phenotypical description of 1,100 cases in Neurology - 2020. See here.