Visual Snow Syndrome is unstable: A longitudinal investigation of VSS symptoms in a Naïve population.

Objective: This study aimed to investigate the nature of subclinical Visual Snow Syndrome (VSS). We sought to develop a means of recruiting naïve participants with subclinical VSS symptoms to participate in research; and to understand whether subclinical VSS symptoms are stable across time. VSS is a recently characterised neurological condition, whose primary symptom is visual snow (dynamic noise in the visual field). There is evidence that VSS may be common in the general population and that it is unnoticed by many who experience it. To fully characterise VSS, it is important to understand whether (and how) subclinical VSS progresses to a clinical form.

Methods: Here, we present two related studies: Study 1 develops and validates the Melbourne Visual Snow Questionnaire (MVSQ), a tool for screening the general population for VSS symptoms; and Study 2 investigates the stability of subclinical VSS. We developed the MVSQ based on the results of other recent work investigating undiagnosed cases of VSS, and a validated questionnaire designed to identify people with tinnitus for research participation. We then tested the MVSQ in a population with clinical VSS, including assessing face validity (i.e., the extent to which people with clinical VSS believed the questionnaire accurately captured their symptoms). In Study 2, we deployed the MVSQ in a naïve sample of 155 participants, who completed the MVSQ twice, 6 weeks apart.

Results: The results of Study 1 indicated that the MVSQ was a viable method of recruiting people who experience VSS symptoms for research participation. It was deemed to have appropriate face validity and to pose little burden to those who completed it. In Study 2, VSS symptoms changed substantially across a 6-week period. Cohen's weighted kappa for diagnosis was 0.56, 95% CI [0.43, 0.69]. However, the impact of perceptual experiences was low and did not change over time, rank ICC = 0.71, 95% CI [0.59, 0.82].

Interpretation: The MVSQ is appropriate for assessing perceptual experiences in the general population. Determining the exact time scale across which symptoms fluctuate is important for understanding both clinical and subclinical cases of VSS.