EFFECTS OF TOPICAL ADMINISTRATION OF 0.5-PERCENT 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 cl inically normal conditioned adult dogs of either sex. Procedure-Normal diurnal variation in IOP, pupil size, and resting heart rate were det ermined from 7 AM to 7 PM (day 1). These measurements were repeated on day 2 after topical application of 60 mu l of 0.5% apraclonidine to 1 randomly chosen eye of each dog. The contralateral eye received salin e 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 varia tions in IOP, however, IOP in the apraclonidine-treated eye on day 2 w as not significantly different from day-1 baseline values obtained fro m the same eye. Significant mydriasis (2.1 mm, 29.7%), persisting for up to 8 hours, occurred in apraclonidine-treated eyes. Although apracl onidine did not significantly alter heart rate when all 9 dogs were vi ewed as a group, 4 dogs experienced a 9 to 19.5% reduction in heart ra te 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% apraclo nidine may be a useful adjunct to other antiglaucoma treatment modalit ies in dogs, but is unlikely to be effective as the sole agent in most forms of canine glaucoma.