Atropine-induced intraocular pressure changes and anterior segment structural parameters in dogs assessed by ultrasound biomicroscopy.

Introduction: In dogs, intraocular pressure (IOP) responses to topical atropine administration vary, and the anatomical basis for this variability remains unclear. Materials and methods: Using ultrasound biomicroscopy (UBM), anterior segment morphology was assessed in 52 eyes from 27 clinically normal dogs before and 20 minutes after atropine administration (post-AT). Results: The mean change in IOP was small, but responses varied across eyes. Approximately 29% showed increases considered clinically relevant. Eyes were categorized into a high group (≥4 mmHg increase) and a stable group (<4 mmHg change) according to post-AT IOP change. Ciliary cleft area (CCA) increased significantly in the stable group and was accompanied by posterior-outward displacement of the ciliary body. In the high group, CCA tended to decrease, with relative anterior displacement of the ciliary body, although these changes were not consistently significant across parameters. In contrast, traditional anterior chamber angle parameters did not differ between groups. Discussion: Heterogeneous post-AT IOP responses appear to be associated with group-dependent differences in ciliary body configuration and ciliary cleft morphology. Variation in these structures may reflect underlying anatomical factors associated with IOP variability. UBM-based assessment may help interpretation of atropine-induced IOP changes.