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B Chen, J Danias, F Shen, YL Su, T Filippopoulos, T Mittag; Effect of Urethane Anesthesia on Intraocular Pressure (IOP) in the Rat . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4074.
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Purpose: To evaluate the use of urethane as a general anesthetic to measure IOP in rats by a non-invasive method. Method: 8 male Brown Norway rats, weighing 300∼400g, were used for this study. All IOP measurements were obtained with a calibrated induction/impact tonometer as previously described (Danias, et al., ARVO 2001) under topical anesthesia with 0.5% proparacaine hydrochloride. IOP in awake but restrained (awake IOP) rats was determined immediately before injection of urethane. Urethane was given by intraperitoneal injection at a dose of 0.6∼0.8g/Kg in sterile water. IOP was subsequently measured when the rats became sedated enough to allow measurements without restraining the animal (time 0). IOP was measured every 5 minutes for a period of 20 minutes. For comparison, the same procedure was repeated on the same animal anesthetized with a (4.5:4.5:1) mixture (KXA) of ketamine (100mg/ml), xylazine (20mg/ml), and acepromazine (10mg/ml). Results: There was no statistically significant change in the IOP of rats measured under urethane anesthesia (mean ± SD: 15.7 ± 2.0) when compared with awake IOP (mean ± SD: 15.9 ± 3.3). In addition, no significant difference in IOP measurements between right and left eyes was detected. A significant (P<0.01) reduction of IOP was found in rats anesthetized with KXA mixture at 5 minutes, 10 minutes, 15 minutes and 20 minutes when compared with their awake IOP. IOP declined 25.2% to 40.3% of the awake IOP at the 5 minutes through 20 minutes time period. Conclusion: Urethane has no effect on IOP in normal Brown-Norway rats. It is a useful general anesthetic to sedate animals for obtaining IOP measurements with the induction/impact tonometer.
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