Drs. Cheng and Tempelhoff are correct that postoperative visual loss (PVL) occurs in the absence of negligence by the anesthesiologist. The origin of PVL appears to be multifactorial, and further studies are needed to define the mechanisms. Hence, we opined in the editorial that more data are needed to design strategies for prevention of this devastating complication. Because of the poorly-defined nature of this injury, whether patients should be informed of the risk preoperatively remains a matter of judgment for the individual anesthesiologist and surgeon.
Drs. Cheng and Tempelhoff think it is “indisputable” that we should routinely ask patients about their vision postoperatively. While this seems an easy procedure to implement and a worthwhile recommendation, data are lacking to mandate such a practice. Patients waking up after anesthesia may not be fully responsive, pupil signs can be erroneous, and visual fields might not be assessable. Anesthesiologists do not routinely perform fundoscopy to examine the optic nerve. In the setting of posterior ischemic optic neuropathy, the fundoscopic exam will, early on at least, likely be inconclusive. Also complicating any postoperative visual examination is the fact that symptom onset may occur anywhere from immediately postoperatively to several days later. Serial examinations would be needed. In our opinion, the inavailability of qualified personnel, the questionable cost-benefit ratio, and the low incidence of PVL render this approach, currently, generally not feasible.
The main thrust of Drs. Benumof and Mazzei's comments relate to the device used to position the head during spine surgery. Anesthesiologists are well aware of the necessity to avoid external pressure on the patients’ eyes. Benumof and Mazzei argue that the device they developed allows continuous observation of the eyes without the need to manipulate the foam cushion. Having used this headrest, we agree that it has this advantage. However, we feel that the anesthesiologist should consider also periodically palpating the eyes directly, every 5–30 min, and documenting this on the patient's operative record. With respect to the conventional square foam headrest, this device is, in fact, suitable for the majority of patients. Placing a hand under the foam to intermittently feel the eyes is easily done. That the foam has to be “peeled” or “pressed away” as Benumof and Mazzei point out, is not a major problem because the eyes are in the open portion of the headrest. Moreover, one could argue that the process of moving the foam and perhaps even lifting the head from time to time adds further assurance that the eyes are not subjected to external pressure. In any event, we think these comments regarding the headrest distract the focus from the primary issues raised in the case report of Drs. Lee and Lam, because direct pressure is rarely the cause of postoperative visual disturbances.
We agree with Drs. Benumof and Mazzei that data on the effects of head down tilt and neosynephrine on the ocular circulation are not available. Whether it is advisable to use vasoconstrictors to maintain higher perfusion pressures to the eye in the prone position cannot currently be stated.