Investigating Optic Nerve Sheath Diameter in Prone Position Spinal Surgery Patients: A Pilot Study.

Purpose: This study aimed to evaluate the effect of intraoperative positioning and ocular immobility on the amount of cerebrospinal fluid around the optic nerve in patients undergoing prone spinal surgery by measuring the optic nerve sheath diameter (ONSD) using ultrasound.

Methods: Consecutive participants (n = 15 patients, 30 eyes) were scanned preoperatively, intraoperatively approximately 20 minutes before the end of the surgery, and postoperatively in the post-anesthesia care unit at least 10 min after the completion of the surgery at one academic hospital.

Results: On average, patients who underwent prone spinal surgery had a 21% increase in ONSD intraoperatively, with a positive time-dependent relationship with the overall length of surgery (P $<$ 0.001). ONSDs postoperatively returned to baseline and were not significantly different from preoperative measurements.

Conclusion: Our findings suggest pooling and inadequate clearance of perioptic cerebrospinal fluid during prone spinal surgery that improves following termination of the procedure and return of the patient to an upright position.