Variations in intraocular pressure during closed-system surgical procedures.

True intraocular pressure (IOP) during closed-chamber anterior segment surgery and vitrectomy was measured in rabbits by inserting a miniature pressure sensor directly into the anterior chamber or into the vitreous. Infusion fluid pressure was also measured simultaneously with a sensor in the infusion line. Significant and rapid changes in IOP up to 110 mm Hg were observed during routine anterior segment and vitreous procedures. None of these IOP changes affected infusion line pressure, which was governed solely by the infusion bottle height. Furthermore, raising the infusion bottle produced minimal IOP elevation whenever fluid was flowing into and out of the eye via a surgical instrument or a wound. These results show the limitations of monitoring of infusion line pressure as a means for assessing IOP and stress the need for IOP control during surgery.