LOS ANGELES—“Visual snow” is part of a unique clinical syndrome that is distinct from visual aura in migraine, according to Christoph Schankin, MD, a fellow in the Department of Neurology, University of California, San Francisco, Headache Center. Dr. Schankin discussed visual snow syndrome at the 54th Annual Scientific Meeting of the American Headache Society (AHS). Also known as positive persistent visual disturbance, visual snow is characterized by tiny, usually black and white, dots in the entire visual field that are always present. Patients usually describe these dots as dynamic, meaning that they change their color rapidly and often. Other visual symptoms often linked with this phenomenon include prolonged afterimages, trailing, photophobia, floaters, bright flashes, color swirls, and impaired night vision.
The literature includes scant evidence of this syndrome. A few case series exist, and often patients are diagnosed with persistent migraine aura or a perceptual disorder resulting from hallucinogen use. Most patients who deny intake of illicit drugs have a history of migraine. But is this visual phenomenon migraine aura? Dr. Schankin and colleagues sought to investigate and further characterize this syndrome.
The investigators used survey results provided by the Eye on Vision Foundation (www.eyeonvision.org), a charitable organization devoted to the study of visual snow, floaters, and macular degeneration and support of those afflicted with these conditions. In addition to reported “visual snow,” trailing and prolonged afterimages (palinopsia) were present in 48% and 63% of the surveyed patients, respectively. Entopic phenomena such as floaters and photopsia in the form of bright flashes were reported by 44% and 73% of the patients, respectively. Little objects moving on the blue sky were noted by 57% of the patients, and 41% of patients saw colored swirls when they closed their eyes. Most of the patients described sensitivity to light and impaired night vision.
To further characterize the symptoms, the investigators designed a prospective telephone interview in which patients were asked to describe their visual symptoms in their own words. A total of 120 patient reports were used for the investigators’ study. In the subset of patients whose visual snow was reported as black and white dots, the same additional visual symptoms were reported at a high frequency—between 51% and 84%. Approximately 98% of patients reported at least one of the following additional symptoms—palinopsia, entopic phenomena, photophobia, and impaired night vision. Nearly 95% reported at least three additional visual symptoms.
Forty of the 57 patients with black and white visual snow noted their visual symptoms later in life; 17 had symptoms for as long as they could remember. The 40 patients with late-onset visual snow were asked whether they had had headaches during the week of onset, and 33% said that they had had a headache, while 10% had a visual aura. However, features of typical aura during the continuous visual symptoms were not present. Intake of illicit drugs was rare. The main illicit drug consumed was cannabis. One patient reported having taken LSD, but at much more than one week prior to the onset of visual symptoms. History of migraine was common; more than 54% fulfilled International Headache Society criteria for migraine, and 35% had typical migraine aura. Significant ophthalmology findings were not present.
Dr. Schankin and colleagues concluded that visual snow is almost always associated with additional visual symptoms and that it therefore represents a unique clinical syndrome—the visual snow syndrome—that is distinct from visual aura in migraine. “However, migraine and migraine with aura are comorbidities, and we don’t know at the moment what the pathophysiological link is between these conditions.” Based on their findings, the researchers proposed criteria for visual snow syndrome, which include visual snow, continuous in timing and encompassing the entire visual field, at least three additional visual symptoms, and inconsistency of symptoms with typical migraine aura. Other disorders should be excluded, especially ophthalmology problems and previous drug intake.
—Glenn S. Williams