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, psychoactive substance use |
| 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) is an uncommon neurological condition in which the primary symptom is visual snow, a persistent flickering white, black, transparent, or colored dots across the whole visual field. It is distinct from the symptom of visual snow itself, which can also be caused by several other causes; these cases are referred to as "VSS mimics." Other names for the syndrome include "scotopic sensitivity syndrome", "Meares-Irlen syndrome", and "asfedia."
Other common symptoms are 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. 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.
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. 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.