title: Contralateral conjugate eye deviation during deep brain stimulation of the subthalamic nucleus.
abstract: OBJECTIVE
  Deep brain stimulation of the subthalamic nucleus (STN) in patients with Parkinson disease is often very effective for treatment of debilitating motor symptoms. Nevertheless, the small size of the STN and its proximity to axonal projections results in multiple side effects during high-frequency stimulation. Contralateral eye deviation is produced in a small percentage of patients, but the precise mechanism of this side effect is at present poorly understood.
  
  
  METHODS
  Contralateral eye deviation was produced by high-frequency stimulation of 22 contact sites in nine patients undergoing deep brain stimulation of the STN. The precise locations of these contacts were calculated and compiled in order to locate the stimulated structure responsible for eye deviation.
  
  
  RESULTS
  The mean x, y, and z coordinates associated with contralateral eye deviation were found to be 11.57, 2.03, and 3.83 mm lateral, posterior, and inferior to the anterior commissure-posterior commissure midpoint, respectively. The point described by these coordinates is located within the lateral anterosuperior border of the STN.
  
  
  CONCLUSIONS
  Given that stimulation of frontal eye field cortical regions produces similar contralateral conjugate eye deviation, these results are best explained by electrical current spread to nearby frontal eye field axons coursing lateral to the STN within the internal capsule. Thus, placement of the implanted electrode in a more medial, posterior, and inferior position may bring resolution of these symptoms by reducing the amount of current spread to internal capsule ax-
authors.affiliation: Division of Neurosurgery, Department of Surgery, David Geffen School of Medicine, University of California, Los Angeles, USA.
authors.forename: Donald C
authors.initials: DC
authors.lastname: Shields
authors.forename: Alessandra
authors.initials: A
authors.lastname: Gorgulho
authors.forename: Eric
authors.initials: E
authors.lastname: Behnke
authors.forename: Dennis
authors.initials: D
authors.lastname: Malkasian
authors.forename: Antonio A F
authors.initials: AA
authors.lastname: DeSalles
mesh_terms: D046690:Deep Brain Stimulation / Q000009:adverse effects*; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D015835:Ocular Motility Disorders / Q000209:etiology*; D020531:Subthalamic Nucleus / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology