Abstract
The intraocular pressure was measured at 5-minute intervals with a Perkins applanation tonometer in 5 patients undergoing routine dacryocystorhinostomy under low-tension anaesthesia with a continuous intravenous infusion of trimetaphan (Arfonad), the systolic pressure being maintained at 66 mmHg. Twelve patients undergoing cataract surgery under the same premedication and anaesthesia but in whom the systemic blood pressure was maintained at normal levels served as controls. A sudden and dramatic lowering of the intraocular pressure to very low levels was noted when the systolic blood pressure was reduced to 60 mmHg. It seems likely that a collapse of the choroidal circulation rather than a decreased aqueous formation due to low perfusion pressure is the most likely cause of the sudden lowering of intraocular pressure.