Postoperative visual loss (POVL) is a rare but catastrophic complication after nonocular surgery. Previously POVL has been reported in lengthy, prone, lateral, or cardiopulmonary cases, with extreme blood loss, hemodilution, and hypotension. The author's index case of POVL following a lengthy operation in steep Trendelenburg position (ST) prompted study of the relationship between intraocular pressure (IOP), mean arterial pressure (MAP), and time spent in ST. A 3-year investigation of the relationship between IOP and ST procedures is reported. Ocular perfusion pressure (OPP) was calculated from IOP and MAP in supine position and at 30-minute intervals during ST. At start of surgery, IOP of 37 patients ranged from 9 to 28 mm Hg. At 120 minutes, IOP ranged from 25 to 54 mm Hg. The OPP ranged from 50 to 82 mm Hg at start of surgery and from 21 to 75 mm Hg after 120 minutes. Increased IOP and reductions in OPP in relationship to position change were statistically significant (P < .001), with OPP falling below IOP in 10 cases. Findings suggest a relationship between prolonged ST and reduced OPP, challenging the accepted view that cerebral and ophthalmic circulatory autoregulation prevents elevated compartment pressures and reductions in perfusion.