Static ocular counterroll: Video-based analysis after minimizing the false-torsion factors

Purpose: To determine the validity and usefulness of a newly developed measurement method of static ocular counterrolling (s-OCR) that eliminates false-torsion factors and to test the Jampel hypothesis that s-OCR does not exist. Methods: A lightweight measurement device, consisting of a video camera, a coaxial light source, and a laser pointer projecting a fixation target on the wall, was fixed to a subject's head by means of a mouthpiece. In 11 healthy adults (mean age: 30 ± 15 years), digital images of the right eye were captured while the subject kept his head tilted at a randomly selected angle ranging from 0°to 50°. By a frame-by-frame analysis of movements of the corneal light reflex and the iris patterns, OCR was evaluated. Results: Torsional eye movement in the opposite direction to head tilt was found in all subjects. The amount of torsion continuously increased until the head-tilt angle reached 40°. The average (± SD) amplitude of a fitted sine curve was 7.6 ± 3.2°(range: 4.3°-10.3°), and the individual amplitude was significantly larger than the test-retest repeatability of the measurement (±1.7°). Conclusions: The measurement method used in this study provided good test-retest repeatability and ease of application. The characteristics of torsional eye movements that we observed after minimizing the false-torsion factors agree with previous reports supporting the existence of s-OCR.