Analysis of Retinal Structure and Electrophysiological Function in Visual Snow Syndrome: An Exploratory Case Series

Visual Snow: Updates and Narrative Review

PURPOSE OF REVIEW

Visual snow (VS) involves visualization of innumerable dots throughout the visual field, sometimes resembling "TV static." Patients who experience this symptom may also have additional visual symptoms (e.g., photophobia, palinopsia, floaters, and nyctalopia) with a pattern now defined as visual snow syndrome (VSS). This manuscript describes both VS and VSS in detail and provides an updated review on the clinical features, pathophysiology, and optimal management strategies for these symptoms.

RECENT FINDINGS

VS/VSS may be primary or secondary to a variety of etiologies, including ophthalmologic or brain disorders, systemic disease, and medication/hallucinogen exposure. Evaluation involves ruling out secondary causes and mimics of VS. Increasing evidence suggests that VSS is a widespread process extending beyond the visual system. Pathophysiology may involve cortical hyperexcitability or dysfunctional connectivity of thalamocortical or attention/salience networks. VSS is typically a benign, non-progressive syndrome and can be managed with non-medicine strategies. Though no medication provides complete relief, some may provide partial improvement in severity of VS.

Adapting to Visual Noise Alleviates Visual Snow

Purpose

Visual snow syndrome-characterized by flickering specks throughout the visual field and accompanied by other symptoms-can disrupt daily life and affects roughly 2% of the population. However, its neural bases remain mysterious, and treatments are lacking. Here, we report the first intervention that can temporarily eliminate the visual snow symptom, allowing many observers to see the world without snow for the first time since symptom onset. Prolonged viewing of a visual stimulus strongly reduces the responsiveness of the visual pathways to subsequent stimuli, and we tested whether such adaptation could affect visual snow.

Methods

Participants with visual snow (total n = 27) viewed high-contrast dynamic noise patterns, resembling television static, and then judged the strength of the symptom.

Results

Visual snow was temporarily reduced in strength to the point that it was invisible at longer adaptation durations for most observers. The effect followed typical trends of adaptation for physical stimuli in normally sighted observers: Effect duration increased monotonically with duration of exposure to the adapter and was specific to dynamic noise.

Conclusions

These results establish that spontaneous neural activity in the visual system is causally related to the visual snow percept. Because they perceive this activity, people with visual snow may provide a unique window into the generation and suppression of noise in the visual system. Adaptation allows reliable experimental control over visual snow, and so is a strong candidate for diagnostic testing and a promising tool for further understanding its neural origins, which could in turn aid the development of treatments.