Effects of topical administration of 0.5% apraclonidine on intraocular pressure, pupil size, and heart rate in clinically normal dogs.

OBJECTIVE: To evaluate the effect of 0.5% apraclonidine on intraocular pressure (IOP), pupil size, and heart rate in clinically normal dogs.
DESIGN: Randomized masked saline-controlled case study. ANIMALS: Nine clinically normal conditioned adult dogs of either sex. PROCEDURE: Normal diurnal variation in IOP, pupil size, and resting heart rate were determined from 7 AM to 7 PM (day 1). These measurements were repeated on day 2 after topical application of 60 microliters of 0.5% apraclonidine to 1 randomly chosen eye of each dog. The contralateral eye received saline solution.
RESULTS: Compared with the saline-treated fellow eye, mean IOP in the apraclonidine-treated eye was significantly reduced (3.0 mm of Hg, 16%) 8 hours after treatment. Because of mild day-to-day variations in IOP, however, IOP in the apraclonidine-treated eye on day 2 was not significantly different from day-1 baseline values obtained from the same eye. Significant mydriasis (2.1 mm, 29.7%), persisting for up to 8 hours, occurred in apraclonidine-treated eyes. Although apraclonidine did not significantly alter heart rate when all 9 dogs were viewed as a group, 4 dogs experienced a 9 to 19.5% reduction in heart rate 2 hours after treatment. Mild blanching of the conjunctiva occurred in apraclonidine-treated eyes.
CONCLUSIONS: Apraclonidine lowered IOP and, in contrast to cats where it causes miosis, induced mydriasis in dogs. Although heart rate generally is unchanged, it may be reduced in select individuals. CLINICAL RELEVANCE: Topically applied 0.5% apraclonidine may be a useful adjunct to other antiglaucoma treatment modalities in dogs, but is unlikely to be effective as the sole agent in most forms of canine glaucoma.