DirectFlow: A Robust Method for Ocular Torsion Measurement

Measuring involuntary eye movement under specific stimuli is an important way to identify diseases such as balance disorders. Exams based on video-oculography (VOG) equipment are able to detect horizontal and vertical displacements of the pupil. However, detecting torsional movements is still a challenge. Although conventional methods have good accuracy, their results can be influenced by artifacts, such as a torsion center displacement, interference by illumination, reflections, and changes in the pupil dilation. We propose a novel method which improves the robustness of this measurement by applying the Lucas-Kanade Pyrm (LKP) optical flow technique to the captured image, directly over the iris, rather than making a polar transformation. Retaining this additional information allows multiple features over the iris to be analyzed individually and as a group, providing correction of the torsion center displacements, filtering features with reflections and adapting to different pupil dilations before the torsion angle is calculated. The accuracy and performance of this method were evaluated by comparing it against a conventional method when detecting torsional movements on videos with a known ground truth. Moreover, a simplified version of the proposed method is also evaluated, in order to analyze the impacts of a torsion center displacement. Results show that the proposed method has higher accuracy and equivalent performance to the conventional method.