title: A method for detecting optokinetic nystagmus based on the optic flow of the limbus.
abstract: Optokinetic nystagmus (OKN) is the sawtooth movement of the eye elicited when an observer views a repeated moving pattern. We present a method for identifying the presence and direction of OKN in recordings of the eye made using a standard off-the-shelf video-camera or webcam. Our approach uses vertical edge detection to determine the limbus/iris boundary, and we estimate the velocity of the edge using Lucas-Kanade optical flow. Heuristic rules are applied to identify saccadic velocity peaks from the resulting velocity signal. The normalized average of the resulting peaks is used to estimate the presence/direction of OKN. Our preliminary testing with six participants observing global motion stimuli with full or partial coherence yields an accuracy of 93% which compares favorably to the performance of an experienced human observer (98% accuracy). Additional tests using high contrast, square-wave gratings show that performance of the technique is consistent at stimulus speeds of 5 and 10deg/s and that OKN is not reported by the algorithm when participants view stationary stimuli.
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, New Zealand; Department of Optometry and Vision Science, Faculty of Medical and Health Sciences, Auckland, New Zealand. Electronic address: j.turuwhenua@auckland.ac.nz.
authors.forename: Jason
authors.initials: J
authors.lastname: Turuwhenua
authors.affiliation: Department of Optometry and Vision Science, Faculty of Medical and Health Sciences, Auckland, New Zealand. Electronic address: sandy.yu@auckland.ac.nz.
authors.forename: Tzu-Ying
authors.initials: TY
authors.lastname: Yu
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, New Zealand. Electronic address: zmazharullah@gmail.com.
authors.forename: Zan
authors.initials: Z
authors.lastname: Mazharullah
authors.affiliation: Department of Optometry and Vision Science, Faculty of Medical and Health Sciences, Auckland, New Zealand. Electronic address: b.thompson@auckland.ac.nz.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Thompson
mesh_terms: D000328:Adult; D000465:Algorithms; D006801:Humans; D016850:Limbus Corneae / Q000502:physiology*; D009039:Motion Perception / Q000502:physiology; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D057849:Optic Flow / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D012438:Saccades / Q000502:physiology; D014741:Video Recording
keywords: Optic flow; Optokinetic nystagmus; Random-dot-kinetogram; Video-oculography