A rare but terrible complication of vision loss has been known to occur after surgery, including spine surgery. It is commonly thought that increased intraocular pressure (IOP) is one of the reasons for this rare vision loss. It has been shown that the prone position can increase the IOP, and that tilting the patient with the head down can also increase IOP. The investigators will be measuring IOP before, during, and after a posterior spine surgery to see if the investigators can influence the intraocular pressure with elevated head position change. Two groups will be studied: one group of patients will receive standard care with the head in neutral position, while the other group will have the head slightly elevated 10 degrees during prone spine surgery.