title: Intraoperative monitoring of visual evoked potential: introduction of a clinically useful method.
abstract: OBJECTIVE
  To obtain a clinically useful method of intraoperative monitoring of visual evoked potentials (VEPs), the authors developed a new light-stimulating device and introduced electroretinography (ERG) to ascertain retinal light stimulation after induction of venous anesthesia.
  
  
  METHODS
  The new stimulating device consists of 16 red light-emitting diodes embedded in a soft silicone disc to avoid deviation of the light axis after frontal scalp-flap reflection. After induction of venous anesthesia with propofol, the authors performed ERG and VEP recording in 100 patients (200 eyes) who were at intraoperative risk for visual impairment.
  
  
  RESULTS
  Stable ERG and VEP recordings were obtained in 187 eyes. In 12 eyes, stable ERG data were recorded but VEPs could not be obtained, probably because all 12 eyes manifested severe preoperative visual dysfunction. The disappearance of ERG data and VEPs in the 13th eye after frontal scalp-flap reflection suggested technical failure attributable to deviation of the light axis. The criterion for amplitude changes was defined as a 50% increase or decrease in amplitude compared with the control level. In 1 of 187 eyes the authors observed an increase in intraoperative amplitude and postoperative visual function improvement. Of 169 eyes without amplitude changes, 17 manifested improved visual function postoperatively, 150 showed no change, and 2 worsened (1 patient with a temporal tumor developed a slight visual field defect in both eyes). Of 3 eyes with intraoperative VEP deterioration and subsequent recovery upon changing the operative maneuver, 1 improved and 2 exhibited no change. The VEP amplitude decreased without subsequent recovery to 50% of the control level in 14 eyes, and all of these developed various degrees of postoperative deterioration of visual function.
  
  
  CONCLUSIONS
  With the strategy introduced here it is possible to record intraoperative VEPs in almost all patients except in those with severe visual dysfunction. In some patients, postoperative visual deterioration can be avoided or minimized by intraoperative VEP recording. All patients without an intraoperative decrease in the VEP amplitude were without severe postoperative deterioration in visual function, suggesting that intraoperative VEP monitoring may contribute to prevent postoperative visual dysfunction.
authors.affiliation: Department of Neurosurgery, Fukushima Medical University, Hikarigaoka, Fukushima, Japan. tsasaki@fmu.ac.jp
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sasaki
authors.forename: Takeshi
authors.initials: T
authors.lastname: Itakura
authors.forename: Kyouichi
authors.initials: K
authors.lastname: Suzuki
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Kasuya
authors.forename: Ryoji
authors.initials: R
authors.lastname: Munakata
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Muramatsu
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Ichikawa
authors.forename: Taku
authors.initials: T
authors.lastname: Sato
authors.forename: Yuji
authors.initials: Y
authors.lastname: Endo
authors.forename: Jun
authors.initials: J
authors.lastname: Sakuma
authors.forename: Masato
authors.initials: M
authors.lastname: Matsumoto
mesh_terms: D000328:Adult; D000368:Aged; D018686:Anesthetics, Intravenous / Q000627:therapeutic use; D002648:Child; D004596:Electroretinography / Q000295:instrumentation / Q000379:methods*; D005074:Evoked Potentials, Visual; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation / Q000379:methods*; D019635:Neurosurgical Procedures / Q000295:instrumentation / Q000379:methods*; D010775:Photic Stimulation; D015742:Propofol / Q000627:therapeutic use; D015203:Reproducibility of Results; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D016896:Treatment Outcome; D014786:Vision Disorders / Q000517:prevention & control
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol