Sufferers of a rare vision disorder that causes them to see the world through a veil of static, appear to process visual stimuli faster than healthy people, leading to hyper-accelerated eye movements, a Monash University study has found.
The study, led by Associate Professor Joanne Fielding from the Department of Neuroscience at Monash’s Central Clinical School, has provided researchers with the first evidence of objective and quantifiable behavioural changes in patients with Visual Snow Syndrome (VSS).
Published in the journal Neurology, the findings provide a behavioural signature of VSS – the essential first step in defining and identifying the areas and processes of the brain responsible.
the brain incorrectly processes visual information sent from the eye, leaving sufferers viewing the world through the hallmark symptom of constant visual snow in their field of vision
The condition is considered to be relatively rare, with many patients unaware they have it or not realising that it is abnormal. The cause of VSS is unknown and eye tests of individuals with VSS do not signal any abnormalities.
It is now believed to be a neurological problem, whereby the brain incorrectly processes visual information sent from the eye, leaving sufferers viewing the world through the hallmark symptom of constant visual snow in their field of vision. Its impact on those who experience the condition is immense, affecting their capacity to work, socialise and have effective relationships with others.
The study used three different ocular motor tasks – prosaccade (PS), antisaccade (AS), and interleaved AS-PS tasks – which placed different demands on the ocular motor-eye movement brain network, allowing the team to determine at which stage visual processing was affected.
They found that, “compared to controls, the VSS group generated significantly shortened PS latencies (p = 0.029) and an increased rate of AS errors (p = 0.001), irrespective of the demands placed on visual processing (i.e., task context). Switch costs, a feature of the AS-PS task, were comparable across groups, and a significant correlation was found between shortened PS latencies and increased AS error rates for patients with VSS (r = 0.404)”.
Associate Professor Fielding said, “The ocular motor network and its processing of visual information is complex, involving a number of distinct steps for us to make sense of how we see the world.”
The network includes areas of the brain involved in sending visual information from the eyes to the vision processing areas of the brain. It then puts together this visual information using cognitive processes to make a cohesive image, supporting the generation of an eye movement.
“Ultimately, this work can be used to develop targeted treatments and better clinical management of this debilitating syndrome,” Associate Professor Fielding said.
Read the full paper in Neurology titled: Ocular motor measures of visual processing changes in visual snow syndrome.
Solly Emma J, Clough Meaghan, M, McKendrick Allison, White Owen B, Fielding Joanne. Ocular motor measures of visual processing changes in visual snow syndrome. Neurology. July 16, 2020, DOI: doi.org/10.1212/WNL.0000000000010372