Visual fields in patients with posterior GPi pallidotomy

Area of Science:

• Neurosurgery
• Ophthalmology
• Neurology

Background:

• Parkinson's disease treatment often involves surgical interventions like pallidotomy.
• Posterior globus pallidus internus (GPi) pallidotomy carries a risk of visual field defects due to proximity to the optic tract.
• Previous studies report variable incidence (0-40%) of visual field defects post-pallidotomy.

Purpose of the Study:

• To determine the incidence and types of visual field defects following posterior GPi pallidotomy.
• To assess the safety of the procedure concerning visual function.
• To identify factors correlating with visual field defects.

Main Methods:

• Goldmann visual field testing was conducted on 40 patients undergoing microelectrode-guided posterior GPi pallidotomy.
• The optic tract was identified using evoked responses to light flashes and stimulation-induced subjective responses.
• Lesioning thresholds were adjusted post-procedure, and lesion locations were confirmed with MRI.

Main Results:

• Three patients (7.5%) experienced visual field defects, specifically contralateral homonymous superior quadrantanopias.
• The incidence of defects decreased from 11% with lower thresholds to 4.5% after increasing lesioning thresholds.
• Lesion proximity to the optic tract was the primary factor associated with visual field defects.

Conclusions:

• Microelectrode-guided posterior GPi pallidotomy is generally safe for visual function.
• Modifying lesioning parameters and careful placement relative to the optic tract can minimize visual field defects.
• The procedure's safety is maintained even when using the optic tract as a landmark.