From the data presented here, almost all patients with ‘visual snow’ have a variety of additional visual symptoms (palinopsia, enhanced entoptic phenomena, photophobia, and nyctalopia), which do not sound like typical migraine aura at all. Visual snow therefore represents a unique clinical syndrome. Our data acknowledge an overlap of migraine and visual snow but do not support the hypothesis that migraine attacks or individual episodes of migraine aura ‘cause’ visual snow. Our data do not support a view the visual snow syndrome is caused by anxiety, depression or the intake of illicit drugs, such as LSD. Remarkably, most patients with visual snow have normal best corrected visual acuity, perimetry and fundoscopy. Any association with visual loss or acute onset of visual symptoms similar to visual snow, especially floaters and photopsia, would therefore require appropriate assessment by a specialist before calling it ‘visual snow’.
We would define the ‘visual snow’ syndrome by the presence of visual snow as the main criterion, with some additional visual criteria, and exclusion of migraine aura, and overlapping diseases, such as ophthalmological pathology or intake of psychotropic drugs (Table 4).