Effect of mydriasis induced by topical instillations of 0.5% tropicamide on the anterior segment in normotensive dogs using ultrasound biomicroscopy.

Objective: To determine the effect of 0.5% tropicamide and the resultant mydriasis on the anterior segment in normotensive dogs using ultrasound biomicroscopy.

Procedure: Twenty-four dogs without ocular disease underwent ultrasound biomicroscopic examination of both the eyes under general anesthesia. Pharmacologic mydriasis was induced in the right eye of each dog by the topical instillation of 0.5% tropicamide. Ultrasound biomicroscopic examinations were performed and the anatomical parameters of the anterior segment were evaluated including the geometric iridocorneal angle (ICA) - formed by the plane of the iris root and the internal corneoscleral limbus - the width of the opening of the ciliary cleft (CC), the width of the mid-CC, the length of the CC, and the anterior chamber (AC) depth (distance between the corneal endothelium and the anterior lens capsule).

Results: Mydriasis resulting from the topical use of 0.5% tropicamide is associated with an increase in the geometric ICA and a decrease in the opening of the CC, without any effect on the width of the mid-CC, or on the length of the CC, or on the AC depth.

Conclusions: Mydriasis induced by topical 0.5% tropicamide results in modification of the anterior segment which may influence the drainage of aqueous humor.