TMS-evoked phosphenes and oculomotor responses in visual-snow syndrome

Visual Snow Syndrome (VSS) is a neurological condition characterized by continuous visual disturbances resembling television static across the visual field. Despite its significant impact on quality of life, objective assessment methods remain limited, with diagnosis relying primarily on subjective patient reports. Current understanding of VSS pathophysiology suggests cortical hyperexcitability, but precise mechanisms remain unclear. Here we developed an integrated protocol combining transcranial magnetic stimulation (TMS)-evoked phosphene mapping with high-resolution eye-tracking analysis. Four VSS patients diagnosed and eight age-matched healthy controls participated. Using individualized MRI-guided navigation, TMS pulses were delivered to occipital cortex regions. After each pulse, participants indicated perceived phosphene locations on a digital tablet. Eye movements were recorded continuously using a Tobii eye-tracker at 120 Hz. Participants completed prosaccade tasks to assess basic oculomotor function, and post-TMS oculomotor responses were analyzed. The VSS participants had significantly altered phosphene perception patterns with more diffuse spatial distribution compared to the controls more centralized and concentrated patterns. Prosaccade latencies were significantly shorter in VSS participants compared to healthy controls. Post-TMS oculomotor responses showed markedly reduced saccadic velocity in the VSS patients versus controls. Thus, the combination of phosphene mapping and eye-tracking analysis provides an efficient tool for VSS assessment and paves the way to uncovering its underlying pathophysiology.