What is "visual snow"

n. (context medical English) A condition in which a person sees television-like static or noise in their field of vision, especially when against a dark background

Visual snow or visual static is a transitory or persisting visual symptom where people see snow or television-like static in parts or the whole of their visual fields, constantly in all light conditions, even visible in daylight. The severity or density of the "snow" differs from one person to the next; in some circumstances, it can negatively affect a person's daily life, making it difficult to read, drive, perform routine tasks, see in detail (even in bright daylight) or focus correctly because of afterimages and other visual and non-visual symptoms.

Little is known about this rare condition, and it has conventionally been regarded as a variant of migraine aura—though recent research shows this is not the case. It is commonly confused with floaters by opticians and doctors alike when patients describe their symptoms, leading to misdiagnosis as well as underdiagnosis of visual snow. Visual snow is now regarded as a unique syndrome—usually presenting with other symptoms, such as persistent afterimages, photophobia, enhanced blue field entoptic phenomenon and tinnitus.

Research has confirmed a brain hypermetabolism in persons with visual snow, located principally in the right lingual gyrus. Before this, no other cause for visual snow had been identified. Insofar as sufferers of visual snow had undergone ophthalmic, neurological and psychiatric examinations, no systematic problems besides the visual snow were found. The recent research that indicates this disorder occurs in the brain has important ramifications for the possibility of potential treatment. However, standard treatment protocols have yet to be established.