OBJECTIVE To evaluate the effects of a medetomidine-ketamine combination on tear production of clinically normal cats by use of the Schirmer tear test (STT) 1 before and during anesthesia and after reversal of medetomidine with atipamezole. ANIMALS 40 client-owned crossbred domestic shorthair cats (23 males and 17 females; age range, 6 to 24 months). PROCEDURES A complete physical examination, CBC, and ophthalmic examination were performed on each cat. Cats with no abnormalities on physical and ophthalmic examinations were included in the study. Cats were allocated into 2 groups: a control group (n = 10 cats) anesthetized by administration of a combination of medetomidine hydrochloride (80 μg/kg) and ketamine hydrochloride (5 mg/kg), and an experimental group (30) anesthetized with the medetomidine-ketamine combination and reversal by administration of atipamezole. Tear production of both eyes of each cat was measured by use of the STT I before anesthesia, 15 minutes after the beginning of anesthesia, and 15 minutes after administration of atipamezole. RESULTS Anesthesia with a medetomidine-ketamine combination of cats with no ophthalmic disease caused a significant decrease in tear production. The STT I values returned nearly to preanesthetic values within 15 minutes after reversal with atipamezole, whereas the STT I values for the control group were still low at that point. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that a tear substitute should be administered to eyes of cats anesthetized with a medetomidine-ketamine combination from the time of anesthetic administration until at least 15 minutes after administration of atipamezole.

OBJECTIVE To determine the temporal effects on tear flow measurements obtained by use of a Schirmer tear test (STT) I after IM administration of various doses of medetomidine or xylazine to healthy dogs. ANIMALS 5 healthy purpose-bred male Beagles. PROCEDURES Each dog received IM injections of 2.0 mL of physiologic saline (0.9% NaCl) solution (control treatment); 0.1% medetomidine hydrochloride (5, 10, 20, and 40 μg/kg), and 2.0% xylazine hydrochloride (0.5, 1.0, 2.0, and 4.0 mg/kg). Treatments were injected into the semimembranosus muscles; there was at least a 1-week interval between successive injections. Order of treatments was determined via a randomized Latin square crossover design. The STT I was performed on both eyes before (baseline) and 0.25, 0.50, 0.75, 1, 2, 3, 4, 5, 6, 7, 8, and 24 hours after each injection.RESULTS STT I values decreased significantly within 45 minutes after injection of medetomidine or xylazine, which was followed by gradual recovery. The lowest mean STT I value was < 10 mm/min for all sedation treatments, except when dogs received 5 μg of medetomidine/kg. Linear regression of the area under the curve for the 8 hours after administration yielded significant effects for all sedation treatments. CONCLUSIONS AND CLINICAL RELEVANCE IM administration of medetomidine or xylazine to dogs reduced tear flow in a dose-related manner. Artificial tear solution or ophthalmic ointment should be used to protect the ocular surface when these drugs are administered to dogs.