Visual snow – how it started…

It began with a phone call from the Daily Mail. Or, to be precise, from a freelance medical journalist who was writing an article for the Daily Mail. She had been talking to a woman called Chloe, with an interesting neurological problem: she was, she said, a “woman who sees snowflakes even when it’s sunny”. Would I be able to provide her with a comment? Or at least talk through the story? OK, I said, tell me about it. And that’s how it began. When my contact details were published at the end of the subsequent article, I almost immediately began receiving emails and letters from people who shared Chloe’s view of the world. A steady stream of referrals started, and has never stopped since.

Visual snow, unlike the migraine aura phenomena with which it is often confused, affects the whole of the visual fields. It is typically most noticeable against a plain light background, but some people find their night vision badly affected by pixilation. ‘Imagine trying to zoom in on a distant object and take a photograph of it with your smartphone at night’, said one sufferer. ‘That’s what it’s like.’ Patients experiencing visual snow often did not drive at night. Children with visual snow found it difficult to follow lessons on a whiteboard. Their visual acuity was unimpaired, but the symptoms nonetheless could have a marked detrimental effect on everyday life.

A second striking feature of visual snow was the consistency of its associated features. Many sufferers were noticeably more aware of entopic phenomena, that is, floaters, shadows, or squiggles arising from within the eye. Others experienced more photopsias – flashes of light arising from random firing of cells in the retina. Many patients found that they could not suppress what they had just seen. When they moved their eyes, they saw afterimages of what they had just been looking at that could persist for ten or even twenty seconds. Some patients saw trails of images as they moved their eyes from side to side. Many patients also experienced tinnitus, tremors, and anxiety. Far more of them experienced migraines than one would have expected by chance.

Some people experienced more florid visual disturbances. At night, in particular, grainy pixels could arrange themselves into geometric patterns – squares, lattices, starbursts, or wavy lines. These experiences reminded me of the prisoner’s cinema – the visions experienced by prisoners (and hippie volunteers) undergoing extreme sensory deprivation; robbed of external input, the brain’s visual processing systems begin to riff, to generate patterns, colours, hallucinations, to fill in the darkness with self-generated light, and the brain’s internal playlist. I came to understand visual snow as a failure of the normal filtering mechanisms in the brain’s visual processing systems. If we look at a blank surface, we do not need to see the work that goes on to render it in our consciousness; from an evolutionary point of view, we need to be more interested in edges, movement, danger.

As it turned out, I was not the only neurologist interested in visual snow in 2013-14. My old boss and mentor Peter Goadsby, a world-renowned headache specialist who at that time was based in California, had set one of his research fellows the task of tracing visual snow sufferers (which they did using the newly burgeoning social media forums) and recording their experiences. In 2014, Goadsby’s group published a landmark paper in the leading neurology journal Brain, in which they reported the clinical characteristics of more than 200 visual snow sufferers, and presented proposed diagnostic criteria for the condition, which they termed the visual snow syndrome.