Cortical potentials after electrical intraneural stimulation of the optic nerve during orbital enucleation.
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 electrical epidural 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 be obtained 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.


CONCLUSIONS
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.
Department of Neurosurgery, University Medical Center Ljubljana, Zaloška 7, 1000, Ljubljana, Slovenia. mitja.benedicic@kclj.si
Mitja
M
Benedičič
University Medical Center Ljubljana, University Eye Hospital, Zaloška 29a, 1000, Ljubljana, Slovenia.
Matej
M
Beltram
University Medical Center Ljubljana, University Eye Hospital, Zaloška 29a, 1000, Ljubljana, Slovenia.
Brigita Drnovšek
BD
Olup
Department of Neurosurgery, University Medical Center Ljubljana, Zaloška 7, 1000, Ljubljana, Slovenia.
Roman
R
Bošnjak
D000368:Aged; D000369:Aged, 80 and over; D000771:Anesthesia, Intravenous; D004558:Electric Stimulation; D004566:Electrodes; D005074:Evoked Potentials, Visual / Q000502:physiology*; D015353:Eye Enucleation; D005260:Female; D005451:Fluorescein Angiography; D006801:Humans; D008297:Male; D008545:Melanoma / Q000473:pathology / Q000601:surgery; D008875:Middle Aged; D019635:Neurosurgical Procedures; D009900:Optic Nerve / Q000502:physiology*; D018608:Ultrasonography, Doppler; D014604:Uveal Neoplasms / Q000473:pathology / Q000601:surgery; D014793:Visual Cortex / Q000502:physiology*; D000098943:Uveal Melanoma