Visual snow is a neurologic condition that was first systematically and clinically defined in 2014. The main clinical feature is that of an unremitting, positive visual phenomenon present in the entire visual field and characterized by uncountable tiny flickering dots. In addition to this “static” phenomenon, patients with visual snow can experience visual symptoms of either direct neurologic origin, such as palinopsia, photophobia, and impaired night vision, or that arise from the optic apparatus, such as the entoptic phenomena. Different combinations of these additional symptoms, together with the static itself, constitute the visual snow syndrome. In the past few years, recognition of visual snow syndrome has grown considerably in both clinical neurology and neuroscience. Nonetheless, the pathophysiology, causes, and treatment of visual snow remain largely unknown.
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• Visual snow is a relatively recently described neurologic disorder characterized chiefly by visual static, resembling a detuned television.
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• The visual snow syndrome is characterized by visual snow plus other distracting visual symptoms such as palinopsia, entoptic phenomena, nyctalopia, and photophobia.
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• The pathophysiology of visual snow is not well understood and there are no clearly established treatments.
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• The most frequent comorbidities of visual snow are migraine and tinnitus.
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• Visual snow should be clinically differentiated from prolonged migraine aura and hallucinogen persisting perception disorder.
Historical note and terminology
Early clinical reports of visual snow have mostly been described in the context of larger case series of migraine patients and were defined with terms such as: “persistent positive visual phenomena” (18), “persistent positive visual disturbances” (14), or “persistent visual aura without infarction” (33; 06).
The first clear description of visual snow as a unique clinical phenomenon can be found in a case report of a young female patient published in the medical literature in 2013 (29). In this paper, visual snow was also termed “positive persistent visual symptoms”.
A study published the following year provided the first systematic characterization of visual snow, distinguishing it clearly from migraine with and without aura (25). This paper also outlined criteria for visual snow syndrome that are currently in use (Clinical manifestations section).