Intraoperative monitoring of visual evoked potential: introduction of a clinically useful method Clinical article
ABSTRACT 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.
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.
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.
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.
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Article: Time to revisit VEP monitoring?Acta Neurochirurgica 02/2010; 152(4):649-50. DOI:10.1007/s00701-010-0601-1 · 1.79 Impact Factor
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ABSTRACT: Visual evoked potential (VEP) has been installed as one of the intraoperative visual function monitoring. It remains unclear, however, whether intraoperative VEP monitoring facilitates as a real time visual function monitoring with satisfactory effectiveness and sensitivity. To evaluate this, relationships between VEP waveform changes and postoperative visual function were analysed retrospectively. Intraoperative VEP monitoring was carried out for 106 sides (eyes) in 53 surgeries, including two intraorbital, 36 parasellar and 15 cortical lesions in Shinshu University Hospital under total intravenous anaesthesia. Red light flash stimulation was provided to each eye independently. VEP recording and postoperative visual function were analysed. In 103 out of 106 sides (97%), steady VEP monitoring was recorded. Stable VEP was acquired from eyes having corrected visual acuity greater than 0.4. VEP was not recorded in one side with corrected visual acuity of 0.3 and two sides in whom sevoflurane was used incidentally for anaesthesia. Transient VEP decrease was observed in three sides, but visual function was preserved. Permanent VEP decrease was seen in seven sides, which presented visual impairment postoperatively. In one side, visual acuity improved but minor visual field defect was encountered postoperatively, though VEP unchanged throughout the surgery. Intraoperative monitoring of VEP predicts postoperative visual function: reversible change in VEP means visual function to be preserved. Visual field defect without decrease in the visual acuity may not be predicted by VEP monitoring. Intraoperative VEP monitoring will be mandatory for surgeries harbouring a risk of visual impairment.Acta Neurochirurgica 04/2010; 152(4):643-8. DOI:10.1007/s00701-010-0600-2 · 1.79 Impact Factor
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ABSTRACT: The aim was to present cortical potentials after intraoperative electrical epidural stimulation of the optic nerve (ON) in individuals with normal preoperative vision. Optic nerve potentials after flash and electrical stimulation were additionally recorded. Contact electrodes on ON and occiput were used for monopolar recording of optic nerve potentials and cortical potentials, respectively. Epidural stimulating electrodes on ON were used to deliver a rectangular current pulse (intensity 0.2-5.0 mA; duration 0.1-0.3 ms; rate 2 Hz), and LED flash goggles were used for flash stimulation. Optic nerve potentials after flash stimulation predominantly consisted of a positive deflection with a latency around 40 ms, followed by a longer-lasting negativity with the peak at around 50 ms. Optic nerve potentials after electrical epidural stimulation of ON were comprised of a negative deflection at around 3 ms. A positive and a negative deflection at 20 and 30 ms, respectively, and a smaller positive deflection at 40 ms constituted cortical potentials after electrical epidural stimulation of ON. Stable and repeatable cortical potentials after electrical epidural stimulation of ON could safely be recorded in humans during neurosurgery. The origin of these presumably far-field potentials and their potential role in intraoperative monitoring remains to be established.Documenta Ophthalmologica 03/2011; 122(2):115-25. DOI:10.1007/s10633-011-9265-2 · 1.11 Impact Factor