Early Ocular Response to Visual Motion in Patients With Persistent Postural-Perceptual Dizziness.

Persistent postural-perceptual dizziness (PPPD) patients with visual dependency rely more on visual cues and may have altered oculomotor responses to visual motion. This study examined early eye movement responses to large-field motion stimuli-the ocular following responses (OFRs)-in 30 PPPD patients and 29 healthy controls. Participants viewed horizontal motion in peripheral and/or central visual fields while eye movements were recorded. OFR velocity 200 ms after stimulus onset and suppression efficacy were analyzed across four central field sizes from 5° to 42° radius. Both groups exhibited strong OFRs to stimuli in the central visual field that increased with the size of the stimulation area. When the central visual field was stationary and the surrounding area moved, patients showed significantly higher eye velocity than controls. Both groups could partially suppress OFRs, but healthy controls were more effective at suppressing eye movements during peripheral stimulation. Patients also showed greater visual dependency on the dynamic subjective visual vertical (2.2° vs. 1.2°), which correlated with OFR magnitude. Overall, PPPD patients were less able to keep their eyes still during peripheral visual motion, producing greater retinal slip and disrupting volitional fixation-an abnormality that may contribute to dizziness and discomfort in visually complex environments.