LOS ANGELES – So-called visual snow, characterized by myriad persistent tiny dots throughout the visual field, commonly occurs in patients with migraine, but it is usually accompanied by other visual symptoms and appears to be a distinct entity, according to combined data from two cross-sectional studies.
In a two-part study among 240 patients with visual snow, nearly all had other visual symptoms such as after-images or poor night vision, reported lead investigator Christoph Schankin, Ph.D., a postdoctoral clinical research fellow at the University of California at San Francisco Headache Center. Slightly more than half also had migraine, but the visual snow did not have any of the features of typical aura. Also, only a small minority of affected patients had used illicit drugs.
"Visual snow is almost always associated with additional visual symptoms. It therefore represents a unique clinical syndrome – the visual snow syndrome," he said at the annual meeting of the American Headache Society. "It is distinct from visual aura in migraine; migraine with and without aura are common comorbidities, but we don’t actually know at the moment what is the pathological link between those two conditions. And the intake of illicit drugs is not relevant."
Dr. Schankin went one step further, proposing new diagnostic criteria for the visual snow syndrome: visual snow plus at least three additional visual symptoms out of nine identified in the study, in the context where these symptoms are not consistent with typical migraine aura and cannot be attributed to some other disorder.
A session attendee congratulated the investigators on the research, noting, "These patients, for those who haven’t seen them, are devastated and lonely. Some can’t drive, some can’t work, some can’t read books, some can’t use computers. They are a wreck ... and there is nobody out there who is owning this condition – I don’t know if it falls in the realm of neuro-ophthalmology or neurology or headache, and what to do with these poor folks. ...They have been banished to the realms of psychiatry and have been told they have functional disorders and other things, when it is very clearly a widespread neurological perceptual disturbance."
He said his own experience with affected patients affirms the existence of the visual snow syndrome. "The more you talk to them, the more you appreciate that they really do have these features in common ... So I just want to thank you for bringing attention to this sort of orphan disorder, and hope it raises awareness, and that some people will take interest in it and studying the biophysiology and treatment options."
Session chair Dr. R. Allan Purdy, a neurologist at Dalhousie University in Halifax, N.S., asked the neuro-ophthalmologists present to weigh in with their thoughts on the possible pathophysiology of visual snow.
"I think this is a somewhat migrainous phenomenon in people with very sensitive brains," one replied. "We have done EEGs on these people and they are normal, at least in adults that we have seen with this. It is definitely real – these people are not making this up. And we have seen quite a few of these cases in neuro-ophthalmology."
Another concurred, saying "I think it’s real." Moreover, in her opinion, the presence of visual snow alone would be sufficient for diagnosis. "I suspect it’s migrainous because most of these people have migraines. But it’s not aura. I don’t know really what it is. It’s incredibly frustrating because nothing works. You can try every antiepileptic known to mankind, and nothing works. So I agree that this is something we need to pay attention to and help these people."
Dr. Schankin noted that research on visual snow is scarce, and affected individuals suffer in part because of a lack of knowledge about the condition in the medical community. "Patients are commonly given the diagnosis of persistent migraine aura or a posthallucinogen perceptual disorder, especially after LSD intake," he noted.
He and his coinvestigators studied members of an online support group for visual snow (Eye on Vision). In the first part of the study, they analyzed data from an Internet survey among 120 patients that asked about visual symptoms. They were 26 years old on average and about two-thirds were men.
Results showed that in addition to visual snow, nearly all patients reported other visual symptoms, such floaters (73%); persistent visual images (63%); difficulty seeing at night (58%); tiny objects moving on the blue sky (57%); sensitivity to light (54%); trails behind moving objects (48%); bright flashes (44%); and colored swirls, clouds, or waves when their eyes were closed (41%).