Visual Snow Syndrome: Proposed Criteria, Clinical Implications, and Pathophysiology.

PURPOSE OF REVIEW: In this article, we review illustrative case descriptions of both primary and secondary visual snow from our clinic. We discuss recently proposed criteria for visual snow syndrome and offer a slight modification of these criteria. We also discuss the theories on the pathophysiological mechanisms of visual snow, as well as the current approach to treatment.

RECENT FINDINGS: Visual snow is a condition where patients see constant, innumerable flickering dots throughout the visual field, similar to "TV static." Though visual snow was originally described in 1995, there were still fewer than 10 cases in the literature prior to 2014. In the last 4 years, this has grown to approximately 200 cases and there has been a concentrated effort to better understand and characterize this condition. It has become apparent that patients who see visual snow frequently have additional visual and non-visual symptoms, and the consistency of these symptoms has led to proposed criteria for visual snow syndrome. When seeing a patient with visual snow, it is important to rule out a possible underlying secondary etiology. Patients with visual snow syndrome frequently have comorbid migraine, but visual snow appears to be a separate entity from persistent migraine aura. The pathophysiology of this syndrome is not clear, but recent neurophysiologic and neuroimaging studies have helped advance our understanding.