Recent advances in lightweight video oculography (VOG) have transformed vestibular assessment, enabling precise, bedside quantification and analysis of eye movements. Portable VOG has been successfully integrated into clinical evaluations, expanding the diagnostic scope of vestibular testing. Building on the principles of otolith-ocular function, a VOG-based test known as video ocular counter-roll (vOCR) has been recently developed for clinical assessment of otolith function. The vOCR test measures torsional vestibulo-ocular reflex (VOR) in response to lateral head tilt, providing valuable insights into vestibular function and compensation. In this chapter, we review the fundamental principles of otolith-ocular function, outline the technical aspects of vOCR measurement, and discuss its clinical significance in evaluating otolith function.