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A. V. Tkatchenko, T. V. Tkatchenko; Ketamine-Xylazine Anesthesia Causes Hyperopic Refractive Shift in Mice. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3671.
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Mice have increasingly been used as a model for studies of myopia. The key to successful use of mice for myopia research is ability to obtain accurate measurements of refractive status of their eyes. In order to obtain accurate measurements of refractive errors in mice, the refraction needs to be performed alone the optical axis of the eye. This represents a particular challenge because mice are very difficult to immobilize. Recently, ketamine-xylazine anesthesia has been used to immobilize mice before measuring refractive errors. Ketamine-xylazine has been used in combination with tropicamide ophthalmic solution, which was instilled in eyes to induce mydriasis. Although these drugs have increasingly been used to refract mice, neither the effects of ketamine-xylazine anesthesia nor the effects of tropicamide on refractive state of the mouse eye were investigated. The purpose of this study was to analyze the effects of tropicamide eye drops and ketamine-xylazine anesthesia on refraction in mice.
The refractive state of both left and right eyes was determined in alert 40-days-old C57BL/6J mice using a high-resolution automated eccentric infrared photorefractor. The animal to be refracted was immobilized using a restraining platform and each eye was refracted along the optical axis in dim room light (< 1 lux). Following this initial refraction, mydriasis and cycloplegia were induced by 1% tropicamide ophthalmic solution (Alcon Laboratories, Fort Worth, TX), which was used as eye drops. The same mice were refracted 20 min. after application of the eye drops. Following the measurement, animals were anesthetized via intraperitoneal injection of ketamine (80 mg/kg) and xylazine (10 mg/kg), and refracted again within 5 min. after the injection.
We found that animals in our population of 40-days-old C57BL/6J mice were emmetropic (0.0 ± 0.4 D, n = 9). The average refractive errors after the application of 1% tropicamide ophthalmic solution were +0.8 ± 0.8 D (n = 9, P < 0.02). However, ketamine-xylazine anesthesia resulted in a hyperopic shift in refraction. Refractive errors in ketamine-xylazine-anesthetized animals were +6.8 ± 2.4 D (n = 9, P < 0.0001).
Our data suggest that ketamine-xylazine anesthesia should be avoided in studies of refractive eye development in mice and underscore the importance of experimental conditions for measuring refractive errors in mice.
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