There are two primary classes of visual snow. The results of a comprehensive study of visual snow are presented. The study is based on about fifty case studies that have arisen in response to this site since its inception and a subsequent close study of the relevant literature.
In the first class, labeled pulse type visual snow, extraneous dots appear scattered about the visual field suggestive of rain drops on a windshield of a car during very light rain. The dots may be darker or lighter than the average content of the scene. They may also tend to flicker individually, or to appear to swirl around in the visual field (like lines of ants).
In the second class, labeled broadband visual snow, the noise appears as a coarse texture (similar to that seen on a TV turned to a blank channel) of low amplitude obscuring the scene in object space. The noise may appear both lighter and darker than the background.
Rarely the extraneous dots appear to vary in color.
Visual snow is characterized by continuous dynamically flickering dots in the visual field. Most patients also have comorbid migraine. Cortical hyperexcitability is a feature of migraine. Recent studies indicate an association between occipital bending with psychiatric disorders such as depression. Here, we demonstrate a patient with visual snow, migraine with aura, left occipital bending, and cortical hyperexcitability. Treatment response to lamotrigine was objectively assessed by repetitive pattern reversal visual evoked potentials (rVEP).
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