Tears play important roles in the ocular surface immune system and metabolic processes on the avascular portion of the cornea. They ensure a smooth optical surface by lubricating the cornea, conjunctiva, and nictitating membrane.1 Insufficient quantity or quality (or both) of tears decreases lubrication and increases frictional irritation of the ocular surface, which can cause keratoconjunctivitis sicca.2
Anesthetic or sedative drugs reduce tear volume in several species.2–7 In particular, α2-adrenoceptor agonists alone and in combination with other drugs affect tear production during sedation in cats,5 horses,8 and dogs.9,10 For example, 10 to 15 μg of medetomidine/kg significantly lowers STT I values in dogs.9 Furthermore, 2.0 mg of xylazine/kg significantly reduces STT I values at 15 and 25 minutes after IM administration to cats.5 In contrast, 0.5 mg of xylazine/kg has no effect on STT I values at 15 to 25 minutes after IM administration to dogs.4 Therefore, the conclusions for previous studies are limited by differences in drug doses and durations of observation.
The purpose of the study reported here was to determine the temporal effects of various doses of medetomidine and xylazine administered IM to healthy dogs on tear flow measurements obtained by use of an STT I. We hypothesized that both medetomidine and xylazine would affect tear flow of dogs in a dose- or time-dependent manner.
Area under the curve
Schirmer tear test
ColorBar Schirmer tear test, Eagle Vision Inc, Memphis, Tenn.
GraphPad Prism, version 6, GraphPad Software Inc, La Jolla, Calif.
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