Visual snow syndrome

Visual snow syndrome
Visual snow syndrome
Other names	Persistent positive visual phenomenon, visual static, aeropsia
	Illustration of visual snow
Specialty	Neurology, neuro-ophthalmology
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	Visual snow can appear at any time, but it commonly appears at birth, late teenage years, and early adulthood.
Causes	Unknown, 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)
Frequency	Uncommon (understudied)

Visual snow syndrome (VSS) (coined by Liu et al in 1995) is a neurological condition in which the primary symptom is persistent flickering white, black, transparent, or colored dots across the entire visual field. It is distinct from the symptom of visual snow itself, which may be caused by multiple ophthalmic and vascular conditions.

Other common symptoms include palinopsia, enhanced entoptic phenomena, photophobia, and tension headaches. The condition is typically always present and has no known cure, as viable treatments are still under research. Migraines and tinnitus are common comorbidities that are both associated with a more severe presentation of the syndrome.

The cause of the syndrome is unclear. The underlying mechanism is believed to involve excessive excitability of neurons in the right lingual gyrus and left anterior lobe of the cerebellum. Another hypothesis proposes that visual snow syndrome could be a type of thalamocortical dysrhythmia and may involve the thalamic reticular nucleus (TRN). A failure of inhibitory action from the TRN to the thalamus may be the underlying cause for the inability to suppress excitatory sensory information. Another existing theory is that visual snow syndrome is caused by dysfunctional cortical visual processing, or failures in the visual processing in the eye's retina. Research has been limited due to issues of case identification, diagnosis, and the limited size of any studied cohort, though the issue of diagnosis is now largely addressed. Initial functional brain imaging research suggests visual snow is a brain disorder, and recent advances in pathophysiology suggest that it is more specifically a network disorder.