[The visual snow phenomenon]

Introduction: Visual snow is a symptom described by some patients and poorly recognized by ophthalmologists. It consists in the permanent perception of a textured or a snowy vision, sometimes associated with palinopsia, exaggerated perception of the blue field entoptic phenomenon and photophobia. We report a group of patients suffering from visual snow in order to precise its characteristics and discuss its pathophysiology.

Materials and methods: Prospective study of patients diagnosed between September 2010 and December 2012 with a visual snow phenomenon. For each patient, a formal ophthalmologic examination, an Amsler grid test, an automated visual field (central 20°), a color vision test (15 Hue), a full field, a pattern and a multifocal electroretinogram as well as flash and pattern visual evoked potentials (Métrovision^©) were performed. A brain imaging was not systematically performed.

Results: Twelve patients aged 9-48old were included (six men and six women, 85 % of students). Several signs were variably associated with the visual snow phenomenon: palinopsia (50 %), constant blue field entoptic phenomenon (40 %), photophobia (30 %), migraine (30 %); in 20 % of cases, an initial toxic intake was found (20 %).

Discussion: This study highlights the reproducibility of typical symptoms described by patients reporting the visual snow phenomenon. This feature strongly supports the organic origin of the phenomenon. The pathophysiology of this phenomenon, however, remains unclear; the hypothesis of a lower threshold for perception of entoptic images cannot entirely account for the reported symptoms.