Ultrasound Biomicroscopic Study of the Effects of 1% Tropicamide on the Anterior Segment and Ciliary Body in Cats.

Objective: To investigate the effects of 1% tropicamide on intraocular pressure (IOP), anterior chamber morphology, and ciliary body dynamics in cats using ultrasound biomicroscopy (UBM).

Methods: A total of 28 eyes from 14 clinically healthy cats were evaluated before and 30 min after unilateral instillation of 1% tropicamide in the right eye (OD), with the left eye (OS) serving as a control. Parameters assessed included pupil size, IOP, and UBM-derived measurements of the iridocorneal angle (ICA), angle opening distance (AOD), ciliary cleft width (CCW), length (CCL), area (CCA), ciliary body axial length (CBAXL), and ciliary process-scleral angle (CPSA).

Results: Tropicamide significantly increased IOP in the treated eye (OD) but not in the control eye (OS). UBM analysis revealed significant reductions in ICA and CCW in OD, while other anterior chamber and ciliary body parameters showed no meaningful changes. In contrast, no significant alterations were observed in any anterior chamber or ciliary body parameters in OS.

Conclusion: These findings suggest that tropicamide-induced IOP elevation in cats results from anterior chamber angle narrowing, emphasizing the need for caution when using mydriatics in patients at risk for ocular hypertension.