Increase in Intraoperative Intraocular Pressure in the Prone Position.

Introduction: This study aimed to measure the intraocular pressure (IOP) of patients undergoing open surgery in the supine position (control group) and spine surgery in the prone position (spine group) to clarify IOP range and change by posture, determine the risk factors for increased IOP in the prone position, and reduce visual complications after surgery in the prone position.

Methods: A prospective cohort study was conducted in healthy adults (34-83 years of age) with an American Society of Anesthesiologists classification I/II. The spine group was examined for IOP, anterior chamber angle (ACA), and fundus findings the day prior to surgery. On the day of surgery, IOP measurements were taken at fixed time points: immediately after intubation; at 0.5, 1, and 2 h after intubation; at suture closure; and at the end of surgery in the control group. In the spine group, they were taken immediately after intubation; at 0.5, 1, and 2 h after prone position; at suture closure; and immediately and 5 min after returning to the supine position. The risk factors for increased IOP in the prone position were examined.

Results: The control group showed no significant changes in IOP within the normal range (<20 mmHg) during surgery. In the spine group, IOP was higher at each time point than immediately after intubation. IOP increased sharply above the normal range within 1 h after changing from the supine to the prone position and continued to gradually increase until suture closure. IOP decreased 5 min after the patient returned to the supine position. ACA, body mass index, blood loss, time in the prone position, and operative time were not risk factors for increased IOP in the prone position.

Conclusions: Patients were constantly exposed to above-normal IOP during prone spinal surgery. However, neither group reported visual impairment. No risk factors were identified for increased IOP in the prone position.