Effect of general anesthetics on IOP in rats with experimental aqueous outflow obstruction

PURPOSE. TO determine the effect of several common general anesthetics on i ntraocular pressure (IOP) after experimental aqueous outflow obstruction in the rat. METHODS. A single episcleral vein injection of hypertonic saline was used t o sclerose aqueous humor outflow pathways and produce elevated IOP in Brown Norway rats. Animals were housed in either standard lighting or a constant low-level light environment. Awake IOPs were determined using a TonoPen (M entor, Norwell, MA) immediately before induction of anesthesia by either is oflurane, ketamine, or a mixture of injectable anesthetics (xylazine, ketam ine, and acepromazine). For each anesthetic, IOPs were measured immediately after adequate sedation (time 0) and at 5-minute intervals, up to 20 minut es. RESULTS. Awake IOPs ranged from 18 to 52 mm Hg. Ail anesthetics resulted in a statistically significant (P < 0.01) reduction in measured IOP at every duration of anesthesia when compared with the corresponding awake IOP. With increasing duration of anesthesia, measured IOP decreased approximately li nearly for both the anesthetic mixture and isoflurane. However, with ketami ne, IOP declined to 48% +/- 11% (standard lighting) and 60% +/- 7% (constan t light) of awake levels at 5 minutes of anesthesia, where it remained stab le. In fellow eyes, the SD of the mean IOP in animals under anesthesia was always greater than the corresponding SD of the awake mean. Anesthesia's ef fects in normal eyes and eyes with elevated IOP were indistinguishable. CONCLUSIONS. All anesthetics resulted in rapid and substantial decreases in IOP in all eyes and increased the interanimal variability in IOPs. Measure ment of IOP in awake animals provides the most accurate documentation of pr essure histories for rat glaucoma model studies.