Elucidating the Visual Snow Spectrum: A Latent Class Analysis Study.

Objective: People with visual snow syndrome (VSS) experience a range of perceptual phenomena, in addition to visual snow (VS; flickering pinpricks of light throughout the visual field). We investigated the patterns of perceptual phenomena associated with VSS in a large sample of people without prior knowledge of VSS or its associated symptoms. Methods and Measures. Two thousand participants completed a screening questionnaire assessing the frequency and severity of perceptual phenomena associated with VSS. We used latent class analysis (LCA), a clustering technique which identifies qualitatively different subgroups within a given population, to investigate whether the presence (or absence) of VS impacted class structure. Results: Of 1,846 participants included for analysis, 41.92% experienced VS some of the time, including 4.49% who had VSS without prior knowledge. The mean number of perceptual phenomena experienced was 2.03. Optimal four-class LCA solutions did not substantially differ whether VS was included in the model; instead, classes differed in the frequency and total number of symptoms experienced. Discussion. Our results suggest that the perceptual phenomena associated with VSS are likely to be common in the general population and do not necessarily indicate an underlying pathology. We also showed that visual snow itself does not explain the presence of other perceptual phenomena.

Perceived severity of Visual Snow Syndrome is associated with visual allodynia.

OBJECTIVE: To investigate whether sensory sensitivity is associated with the perceived severity of Visual Snow Syndrome (VSS) symptoms. BACKGROUND: Visual Snow (VS) is a perceptual anomaly which manifests as flashing pinpricks of light throughout the visual field. VSS has an estimated population prevalence of 2.2% and is thought to be at least moderately debilitating for all who experience it. However, some people who meet the criteria for VSS have no awareness of it. This may be because they have lower sensory sensitivity, allowing them to ignore their visual phenomena. METHOD: Our study used a cross-sectional design. We recruited two distinct samples of people with VSS: a sample of people with confirmed VSS; and a sample of people who met the criteria for the condition but had no prior knowledge of it (latent VSS). The latter group was recruited and screened for symptoms via an online crowd-sourcing platform. In total, 100 participants with VSS (49 with confirmed VSS, 51 with latent VSS) completed the Visual Snow Handicap Index and three measures of sensory hypersensitivity. RESULTS: The 100 participants (52 female, 47 male, 1 non-binary) had a mean age of 35.1 years (SD = 12.2). Leiden Visual Sensitivity Scale scores were associated with both the perceived severity of VSS, ß = 0.35, p = 0.003, and the number of VSS symptoms endorsed, ß = 0.45, p < 0.001. On average, participants with VSS experienced elevated sensory hypersensitivity across all measures. Furthermore, longer duration of VSS was associated with lower perceived severity, F(1, 98) = 11.37, p = 0.001, R2  = 0.103. CONCLUSIONS: Our results suggest that sensory hypersensitivity may be prevalent in people with VSS and indicate that visual allodynia is associated with increased severity of VSS. Additionally, our findings indicate that inclusion of cases of latent VSS in future research may be important for researchers to develop a more complete understanding of the perceptual experiences of people with VSS.