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 positivedeflection 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 deflectionat 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.
COBISS.SI-ID: 29079001
Clinical test of photoplethysmograph (PPG) prototype developed for intraoperative monitoring of the optic nerve microcirculation was performed. Portable measurement system based on 4-channel transimpedance amplifier and adjustable constant current sources was designed and built for data acquisition of PPG waveforms. During this clinical test, measurement of PPG waveforms at patient’s long toe and optic nerve were performed simultaneously. Using a simple technique to attach PPG prototype to the surface of the optic nerve during this preliminary test, PPG waveform was successfully measured. Beside optic nerve microcirculation, a significant information about respiration was obtained in measured PPG waveform.
COBISS.SI-ID: 10807636
Background: Central skull base meningiomas commonly present with visual deficit, and their removal often leads to improvement of visual function. However, the incidence of postoperative visual deterioration has been reportedto be up to 10%. Intraoperative monitoring using flash visual evoked potential has only recently been used with success. Cortical potentials (CP) after electrical epidural stimulation of the optic nerve (ON) were correlated with ON manipulation due to central skull base tumor removal to contribute to improvement of the intraoperative monitoring of the visual function. Methods: Blunt needle stimulating electrodes were attached epidurally alongside ON in an unroofed optic canal and used for delivering a rectangular current pulse (intensity 0.2-5.0 mA; duration 0.1-0.3 ms; rate 2 Hz). CPs after electrical epidural stimulation of ON were recorded with corkscrew electrodes at O(z) with the reference electrode at F(z). Results: P20 and N30 amplitudes were significantly lower (p ( 0.05) during tumor removal associated with ON manipulation than in other phases of surgery; the amplitude reductions were reversible in all cases. There were no significant changes in P20, N30 and P40 latencies during the surgery. Immediate postoperative visual function was unchanged in all patients. Conclusions: P20 and N30 amplitude changes seem to reliably correspond with the manipulation of ON during anterior skull base tumor removal. Reversible reduction of P20 and N30 amplitude was associated with unchanged immediate postoperative visual function. No correlation betweenintraoperative variation of CP and newly acquired postoperative visual deficit can presently be made.
COBISS.SI-ID: 29116633
Background The aim of this study was to present cortical potentials after electrical intraneural stimulation of the optic nerve during orbital enucleation due to malignant melanoma of the choroid or the ciliary body. These cortical potentials were related to cortical potentials after electricalepidural stimulation of the optic nerve, recorded during non-manipulative phases of neurosurgery for central skull base tumors. Methods Cortical potentials were recorded with surface occipital electrode (Oz) in six patients undergoing orbital enucleation under total intravenous anesthesia. Two thin needle stimulating electrodes were inserted inside the intraorbital part of the optic nerve. The electrical stimulus consisted of a rectangular current pulse of varying intensity (0.2-10.0 mA) and duration (0.1-0.3 ms); the stimulation rate was 2 Hz; the bandpass filter was 1-1,000 Hz; the analysis time was 50-300 ms. Results Cortical potentials could not beobtained or were inconsistently elicitable in three patients with longstanding history ()3 months) of severe visual deterioration, while they consisted of several positive and negative deflections in a patient with a short history of mild visual impairment. In two other patients, cortical potentials consisted of N20, P30 and N40 waves. Discussion Cortical potentials after electrical intraneural stimulation of the optic nerve could be recorded in patients with a short history of visual deterioration and without optic nerve atrophy and appear more heterogeneous than cortical potentials after electrical epidural stimulation of the optic nerve, recorded during non-manipulative phases of neurosurgery for central skull base tumors.
COBISS.SI-ID: 653228