Causes of Elevated Intraocular Pressure during Prone Spine Surgery

Abstract

We read with attention the letter by Lee et al. regarding our study, “The Effect of Prone Positioning on Intraocular Pressure in Anesthetized Patients.” There are several points in their letter that we would like to address. First, we would like to point out that we titled our study “The Effect …,” rather than “The Causes of Elevated IOP…” since the sole purpose of our study was to observe the effects of prone positioning on intraocular pressure (IOP) in anesthetized patients.Second, while we agree that our IOPs in the prone position might be considered strikingly high by some, we found that the fact that the results were reproducible in 20 patients seems to indicate that they may indeed be real. For the authors of the letter to suggest that the results are too high because none of our patients had visual deficits despite a lowered perfusion pressure is ludicrous, as it is plainly known that perioperative visual loss is extremely rare and of as yet unknown cause(s).Third, the authors of the letter also attempt to justify their claim that our results are flawed by comparing the data from a previous study of awake volunteers 1with those we obtained in anesthetized patients. Extrapolating data from awake volunteers for comparison to anesthetized patients is denying any effects of anesthetics on physiology.Fourth, the authors question our methods in terms of how the IOP was measured. Using a pinned head holder prevents all of the obstacles they delineate in their letter (i.e. , eyelid retraction, and approach to the eye with tonometer).Fifth, it is difficult for us to take at “face value” the authors’ reference to their unpublished data.We appreciate the commentaries and criticisms of our study. This study is just the a piece of the puzzle that is perioperative visual loss. We look forward to seeing further data in this area of research.