Visual snow syndrome

Visual snow syndrome
Other names	Persistent positive visual phenomenon,[1] visual static, aeropsia
Animated example of visual snow-like noise
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[2]
Usual onset	Visual Snow can appear at any time, but it commonly appears at birth, late teenage years, and early adulthood.
Causes	Unknown,[3] hyperexcitability of neurons and processing problems in the visual cortex[4][5]
Risk factors	Migraine sufferer,[6] psychoactive substance use
Differential diagnosis	Migraine aura,[7] Persistent aura without infarction, Hallucinogen persisting perception disorder[8][9]
Medication	Anticonvulsants[7][3] (limited evidence and success)
Frequency	Uncommon (understudied)

Visual snow syndrome (VSS) is an uncommon neurological condition in which the primary symptom is that affected individuals see persistent flickering white, black, transparent, or colored dots across the whole visual field.^[7][4]

Other common symptoms are palinopsia, enhanced entoptic phenomena, photophobia, and tension headaches.^[10][11] The condition is typically always present and has no known cure, as viable treatments are still under research.^[12] Astigmatism, although not presumed connected to these visual disturbances, is a common comorbidity. Migraines and tinnitus are common comorbidities that are both associated with a more severe presentation of the syndrome.^[13] Temporomandibular joint dysfunction (TMJ) may also be a common comorbidity.^{[citation needed]}

The cause of the syndrome is unclear.^[3] 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.^[4][6] 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.^[14]