Dependency-Induced Increase in Intraocular Pressure: A Contributing Factor for Postoperative Visual Loss After Spinal Surgery

INTRODUCTION: Postoperative visual loss, associated with anemia and hypotension, has been reported with increasing frequency in spinal surgery patients.

HYPOTHESIS: Increased intraocular pressure could be induced by mild Trendelenburg positioning, possibly affecting ocular blood flow in these prone, hypotensive patients.

METHODS: Intraocular pressures were measured in 4 subjects in multiple positions.

RESULTS: Subjects were shown to increase their intraocular pressures from an average of 13 mm Hg in the sitting position to 30.75 mm Hg in the prone position when in 7° of Trendelenburg. Pressures then decreased to 17.25 mm Hg after 5 minutes in 7° reverse Trendelenburg.

CONCLUSION: Orbital dependency can increase intraocular pressure. This may, when combined with surgical hypotension, decrease intraocular blood flow and play a role in postoperative visual loss. This effect may be minimized by avoiding Trendelenburg positioning.