Investigators from University of California, San Francisco; King's College London, UK; and University of Utah, Salt Lake City, studied patients with ‘visual snow’ to characterize the phenotype and compare it to migraine aura. Of 22 patients referred with this diagnosis, 15 had additional visual symptoms, and 20 had comorbid migraine, 5 with aura. Visual symptoms included palinopsia (trailing and afterimages), entoptic phenomena (floaters, spontaneous photopsia), photophobia, and nyctalopia (impaired night vision). Duration of visual snow symptoms varied from “as long as they could remember” in 25%, to a mean age of onset of 21 +/- 9 years in the remainder. Symptoms were constant in some and progressive in others. Worsening of visual snow symptoms in 36% cases was associated with headache, migraine, migraine with aura, anxiety and depression. First degree relatives were affected in 8 patients. 
COMMENTARY. ‘Visual snow’ is described as continuous tiny dots in the entire visual field similar to the noise or static of an analogue TV and lasting longer than 3 months. Frequently comorbid with migraine but considered a unique disorder distinct from migraine with aura, complicated by palinopsia, floaters, photophobia, and nyctalopia, and not explained by intake of psychotropic drugs.