We appreciate the interest of Drs. Benumof and Mazzei in our case report of visual loss after an uneventful spine surgery in the prone position in an otherwise healthy patient. 1They expressed concerns about several issues. In particular, their emphasis on “adequacy” of eye-check and padding provides us with the opportunity to address an important issue that we perhaps did not adequately explain in our report, leading to their misunderstanding. Adequate padding of the head in the prone position to prevent pressure on the eyes is important, and in the case we reported, we used a standard foam support (Gentletouch Headrest Pillow, Orthopedic Systems Inc., Union City, CA), with a cut-out for the eyes. Eye-checks can be performed accurately by pressing down on the side of the foam cushion without altering the correct positioning. The patient is of Caucasian extraction with a high nasal bridge. Moreover, the nasal bridge is of no consequence provided that the eyes are positioned correctly in the cut-out portion of the foam cushion.
Of utmost concern is their perseveration regarding the type of foam cushion, the height of the nasal bridge, and the method of eye-checks, which underscores a fundamental lack of understanding, and a common misconception about the pathophysiology of visual loss after spine surgery. 2The ophthalmologic diagnosis in our case report, similar to most cases of visual loss after prone spine surgery, was posterior ischemic optic neuropathy. The lesion lies posterior to the lamina cribosa, sparing the retina, and has never been shown to be related to pressure on the globe. 3Visual loss from pressure on the globe, on the other hand, is secondary to central retinal artery occlusion with or without anterior ischemic optic neuropathy. These patients will frequently show signs of external periorbital bruising or proptosis, with evidence of retinal ischemia, which our patient did not. Moreover, in some patients who develop visual loss after prone spine surgery, Mayfield head pins were used instead of foam cushions, removing all doubts about pressure on the eyes. (ASA Postoperative Visual Loss Registry, unpublished data, 2001). The emphasis on pressure on the eyeballs in the context of postoperative visual loss is akin to the man looking for his keys under the lamppost after dropping them on the lawn; he sees a bright spot but he won't find the keys. While we can all applaud efforts to improve patient safety with foam cushions of better designs (the Dupaco Prone-View foam cushion is certainly a good one), overemphasis on this aspect will divert our attention and focus away from the real pathophysiology and prevention of postoperative visual loss from ischemic optic neuropathy.
As for their final point, we would advise Drs. Benumof and Mazzei to read the original discussion in our case report again 1, where we had raised similar questions, the answers to which are currently unavailable, and should form the focus of concerted research efforts.