Intra Ocular Pressure During Robotic Prostatectomy

The frequency of post-operative permanent vision loss has been recently estimated to be 1:61,0001,2 , although the majority of these cases involve surgical trauma to the eye or brain. Prolonged vision loss not attributable to direct trauma has been estimated to occur with a frequency of approximately 1:125,0003 and has been given a broad classification termed ischemic optic neuropathy. This rare but catastrophic outcome has most commonly been associated with operations performed under circumstances in which there may be increased intraocular pressure (IOP), either due to positioning4 or due to insufflation of the abdomen with carbon dioxide (laparoscopy).5 There are two factors predisposing the robotic prostatectomy patient to an increase in IOP: step head-down (Trendelenburg) position and abdominal carbon dioxide (CO2) insufflation. The Trendelenburg position will increase central venous pressure within the thorax, which may reduce the drainage of blood flow from the head, thus increasing IOP. The CO2 insufflation may increase IOP via two mechanisms. First, by increasing intra-abdominal pressure there is a further increase in intrathoracic pressure. Secondly, insufflation the CO2 may increase the carbon dioxide content of the blood, to which the brain reacts by vasodilating and increasing blood volume. Thus while flow into the eye is increased, flow out of the eye is decreased leading to an increase in pressure inside the eye which eventually may reduce the inflow enough to cause retinal or optic nerve ischemia. Because the pressure within the eye is an important factor in determining the blood flow to the eye, prevention of a dramatic increase in IOP may make patients less vulnerable to peri-operative ischemic optic neuropathy and vision loss. Because permanent vision loss is such a rare event after surgery, this study will measure more subtle (and most likely, temporary) vision changes (subjective blurriness, visual field deficits, decreased acuity), which occur more frequently and are thus a more easily measured outcome.6 As robotic procedures are gaining in popularity, we should determine whether they are subjecting this patient population, and perhaps more likely the patient with a preoperative diagnosis of glaucoma, to an increased likelihood of postoperative visual disturbance.