BREAK IN BINOCULAR FUSION DURING HEAD TURNING IN MS PATIENTS WITH INO

Internuclear ophthalmoparesis (INO) is the most common eye movement abnormality observed in patients with multiple sclerosis (MS).1 While most MS patients with INO have no or little misalignment in the straight ahead position, significant disconjugacy occurs during horizontal saccades or with horizontal (yaw axis) head turning.2 A break in binocular fusion can produce a loss of stereopsis and depth perception, transient diplopia (perceived as a double image or visual blur), oscillopsia, and disorientation.2 The purpose of this investigation was to confirm the hypothesis that a break in binocular fusion occurs in MS patients with INO during head or body turning, and that the magnitude of disconjugacy will be directly correlated with the severity of this eye movement syndrome. ### Methods. Three subject groups were investigated: MS patients with INO (MS-INO; n = 6; 5 bilateral, 1 unilateral for a total of 11 INO); MS patients without INO (MS-CON; n = 3); and healthy normal controls (HC; n = 7). When specifically asked, all of the MS-INO subjects reported impaired vision during head turning, whether with walking or driving. All protocols were approved by the Institutional Review Board at the University of Texas Southwestern Medical Center at Dallas, and were conducted in accordance with the Declaration of Helsinki principles. All study subjects consented to participate in these studies. Recordings were performed in a partially illuminated room using a head mounted 2D infrared oculography device (Eyelink II, SR Research). INO was confirmed by having patients first perform 20-degree horizontal saccades and determining the velocity …