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

Tropicamide elevates feline IOP through anterior chamber angle narrowing; use cautiously.

This prospective controlled study investigated tropicamide's effects on feline ocular parameters using ultrasound biomicroscopy. Twenty-eight eyes from fourteen clinically healthy cats underwent baseline assessment followed by unilateral 1% tropicamide instillation, with contralateral eyes serving as controls. Measurements included pupil diameter, intraocular pressure, and UBM-derived anterior segment parameters including iridocorneal angle, angle opening distance, and ciliary body dimensions. Results demonstrated significant IOP elevation in treated eyes without concurrent changes in control eyes. UBM analysis revealed statistically significant reductions in iridocorneal angle and ciliary cleft width in tropicamide-treated eyes, while other anterior chamber and ciliary body measurements remained unchanged. The contralateral untreated eyes showed no significant alterations in any measured parameters. These findings suggest that tropicamide-induced ocular hypertension in cats results from anterior chamber angle narrowing rather than ciliary body dysfunction. The study emphasizes the importance of IOP monitoring and cautious mydriatic use in feline patients, particularly those predisposed to angle-closure mechanisms or ocular hypertension. Clinical application requires consideration of individual risk factors.

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