Topical caffeine induces mydriasis in animals under ketamine‐xylaxine anesthesia

Abstract

AbstractPurpose To determine the effect of topically applied caffeine on the pupil diameter during ketamine‐xylazine anesthesiaMethods Six‐week‐old Sprague‐Dawley rats were anesthetized with ketamine xylazine intraperitoneally. Caffeine, 72 mM, dissolved in vehicle, 9 mg/ml, hydroxypropylmethyl cellulose dissolved in water, or the vehicle only, was topically applied. Animals were kept under room light conditions. In experiment I, caffeine in vehicle was topically applied to one eye and vehicle only to the other eye in 10 animals. In experiment II, caffeine in vehicle was applied to both eyes in one group of 10 animals and vehicle only to another group of 10 animals. In both experiments, pupil diameter was measured on both eyes. Measurements were taken immediately after initiation of the anesthesia, and 10, 20, 40 and 60 min. later.Results In experiment I, vehicle only caused a slight transient increase of pupil diameter, peaking around 20 min. after initiation of anesthesia and then decreased below baseline. Caffeine in vehicle caused an initial fast decrease in pupil diameter and the decrease rate leveled out towards 60 min. after initiation of anesthesia. In experiment II, vehicle to both eyes induced a transient increase in pupil diameter that returned to baseline. Caffeine and vehicle on both eyes induced an exponentially declining decrease towards asymptote miosis. The miosis reversed to mydriasis after topical application of tropicamide 5 mg/ml.Conclusion Topically applied caffeine induces miosis in a ketamine‐xylazine anesthetized rat. There is some systemic effect on pupil diameter of the currently used topical application of caffeine. The miotic effect of topically applied caffeine is reversed by tropicamide.