New insight to the pathophysiology of vision loss after neurosurgical procedures

In this prospective trial, the authors investigated IOP changes during neurosurgical procedures with opening of the dura mater and loss of cerebrospinal fluid (CSF).

Study design

The trial consisted of 64 patients undergoing neurosurgical procedures with opening of the dura mater and loss of CSF; IOP was measured before, during and after surgery. Patients were divided into four groups: group A had spine surgery in the prone position, group B had intracranial procedures in the prone position, group C had intracranial procedures in a modified lateral position with the head rotated and group D had spine surgeries in the prone position with intact dura.

Outcomes

In all groups, IOP decreased after induction of anesthesia and increased after final positioning for the operation. Investigators found that opening of the dura with loss of CSF resulted in a statistically significant decrease in IOP lasting up to 60 minutes. This effect was independent from the positioning of the head or the procedure itself. 

Limitations

The authors did not measure arterial or end tidal CO_2, the effect of depth of anesthesia on IOP, CSF loss volume or retinal perfusion during surgery. These factors may have affected IOP readings.

Clinical significance

Perioperative visual loss is a rare but serious complication in surgical disciplines, especially in spine surgery. These findings might explain why postoperative vision loss predominantly occurs after spinal surgery, but rarely happens after intracranial procedures.

The evidence here supports the hypothesis that venous congestion in the orbit due to increased IOP, elevated intraorbital venous pressure as well as reduced optic nerve perfusion pressure may be contributing factors that lead to vision loss.