Abstract
PURPOSE: To assess the effects of modifying head position and of static ocular counter-rolling (OCR) on abduction and adduction in saccadic eye movements using a head-mounted video-oculographic device. STUDY DESIGN: A clinical observational study. METHODS: The peak velocities and amplitude gains of visually guided 12° saccades were binocularly measured in 21 healthy volunteers with their heads in the upright vertical (0°) and horizontal (± 90°, bilateral side-lying) postures, and in 6 participants with their head positions bilaterally tilted by 30°. The rotation angles of eyeballs generated via OCR in the bilateral 30° and 90° head positions were evaluated in five participants. RESULTS: Peak velocities and gains were significantly higher with the head in the 0° position compared to ± 90°. The decreases in peak velocities and gains at ± 90° were not affected by the apogeotropic or geotropic directions. Faster peak velocities and greater gains on abduction, rather than adduction, were observed under each test condition. The tendencies toward faster peak velocity and greater gain in the 0° head position rather than bilaterally tilted at 30° were preserved. The absolute rotation angles at ± 90° were larger than those at 30°. CONCLUSIONS: Head position affected the peak velocities and gains of both abduction and adduction saccades. The findings suggest that modified force vectors exerted by different eye muscles recruited during OCR play a role. Our research provides valuable insights for assessing eye movements across various head positions.