Conference Coverage

Visual snow: Alarming and not uncommon


 

FROM 2021 SCOTTSDALE HEADACHE SYMPOSIUM

‘Grainy’ or ‘pixelated’ vision can be an alarming symptom for patients. The phenomenon is called visual snow, and although it was first described only recently, it is fairly common.

“This is a symptom of vision where patients describe numerous flickering dots throughout their vision. Sometimes they’ll use the term grainy or pixelated vision. Many times there’s a dynamic moving component to this. Many patients will describe this as like a TV static overlay on their vision,” Carrie Robertson, MD, said during a presentation on the topic at the 2021 Scottsdale Headache Symposium. Dr. Robertson is a neurologist at the Mayo Clinic in Rochester, Minn.

“It turns out that a little over 3% of us probably see this in our vision. So even if you haven’t seen this in the clinic yet, it’s likely that you will in the future,” said Dr. Robertson.

The first report describing visual snow appeared in 1995, among migraine patients. As of 2014 there were only 10 cases described in the literature. Although the condition was initially thought of as an unusual feature of migraine, a 2014 combined chart review and survey found that 15 of 22 patients had additional visual symptoms, such as photophobia or difficulty with night vision. Twenty of the 22 patients had comorbid migraine. Other symptoms include visual ghosts that persist after looking away from an object, as well as a higher frequency of experiencing floaters.

Symptoms aren’t restricted to the visual domain. Migraine, tinnitus, dizziness, and impaired concentration also occur.

The condition is more common than many suspect. “We used to think it was very rare. Now we assume that this was just under recognized,” said Dr. Robertson. One survey in the United Kingdom found that 3.7% of respondents reported visual snow, and 2.2% met the criteria for the syndrome.

A common and typically benign problem

It is a common clinical problem, according to Andrew Charles, MD, professor of neurology at the University of California, Los Angeles, and director of the UCLA Goldberg Migraine Program. “Almost every week I personally see somebody and then in our group, we have a whole host of them,” he said.

“When you see these patients in clinic, it’s important to remember that this is a heterogeneous disorder,” said Dr. Robertson. “Some patients will say, ‘Oh yeah, I’ve seen visual snow for as long as I can remember, I didn’t even know it was abnormal.’ Some will describe a family history of visual snow. Others will show up in clinic panicked because their visual snow just started or sometimes it’ll start after a triggering events like a head injury or hallucinogen use, and they’re worried that they’re going to go blind.”

It’s important to rule out other potential causes. Dr. Robertson’s group examined 248 cases of visual snow and found that 89 had a comorbidity that explained the condition. Issues within the retina, cornea, and the optical nerve can cause visual snow, which makes it critical that patients be seen by an ophthalmologist.

Some patients reported improvement when they stopped a new medication. “I always ask if there was a specific medicine that they started at the onset of their symptoms,” said Dr. Robertson. Other rare conditions associated with visual snow include idiopathic intracranial hypertension, posterior cortical atrophy, and even the Heidenhain variant of Creutzfeldt-Jakob disease.

In the absence of a secondary cause, and the if condition doesn’t worsen, physicians should reassure patients that the condition is typically benign. “Many of these patients are panicked that they’re going to lose their vision, and that’s what brings them to your office. It’s important to stress that visual snow is real, that you believe them, that they’re seeing what they say that they’re seeing. It’s not a migraine aura, but it’s typically benign. I like to give the analogy that it’s similar to tinnitus because I think that that’s helpful for patients to put it in that category of benign but very annoying,” said Dr. Robertson.

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