Visual snow is a rare neurological condition where people see static-like ‘snow’ (continuous tiny dots similar to the noise of an analogue TV) in their vision all of the time. Other common complaints are seeing afterimages and excessive floaters and experiencing tinnitus. The precise cause of visual snow is not understood, however, symptoms are thought to be due to excessive neural firing in the visual areas of the brain (cortical hyperexcitability).
In this study, we tested patients with visual snow on four visual perceptual tasks that are believed to indirectly measure visual cortical hyperexcitability. Two of the tasks, luminance increment detection in spatial noise and centre surround contrast matching, were chosen as they test early stages of the visual processing. The other two tasks, global form perception and global motion discrimination, assess relatively later stages of the visual processing pathway.
We found that people with visual snow process luminance and contrast differently from controls, consistent with elevated excitation in the early stages of the visual processing pathway (higher luminance increment detection threshold and higher perceived contrast in the presence of a high contrast surround grating). This work reveals promise for the future development of visual tests that may help differentiate visual snow from other disorders and quantify the effectiveness of treatments.
The paper has been published in Neurology and was conducted in collaboration with Assoc Prof Owen White from Melbourne Health (Royal Melbourne Hospital); and Assoc Prof Joanne Fielding from Monash University. To access a full copy of the paper, please contact Allison directly at firstname.lastname@example.org