Effects of General Anesthesia on Intraocular Pressure in Rabbits

Measurement of intraocular pressure (IOP) is a standard procedure in ophthalmic research in animals, specifically in glaucoma research, and the control of IOP is essential during certain veterinary ophthalmic surgeries. We evaluated the effect of isoflurane on IOP in the clinically healthy laboratory rabbits and tested a way to minimize the alteration of IOP during isoflurane anesthesia. After measurement of the baseline IOP in each eye of 9 awake New Zealand white rabbits, animals were anesthetized by using either: (1) isoflurane without premedication, (2) a combination of ketamine and xylazine, or (3) isoflurane inhalation after an injection of ketamine-xylazine premedication. Isoflurane led to a sustained increase in IOP of approximately 12 mm Hg. In contrast, ketamine and xylazine decreased IOP by nearly 5 mm Hg (all values compared with baseline measurements in awake, unrestrained animals). The observed decrease in IOP after ketamine-xylazine anesthesia is consistent with anesthetic effects generally seen during anesthesia in other studies. The increased IOP after isoflurane anesthesia in rabbits in this study was an unexpected result that appears to be specific to this combination of anesthetic and animal species. Premedication with ketamine-xylazine diminished the effect of isoflurane inhalation on IOP. These results should be considered in the design of ophthalmic research studies using rabbits and in intraocular surgery where IOP stability is desired.