Background: We report 2 cases in which ultrasound biomicroscopy (UBM) was used to diagnose Ahmed valve obstruction by the iris.
Methods: Two patients underwent unilateral placement of Ahmed implants, one into the anterior chamber and the other into the ciliary sulcus.
Results: Intraocular pressures increased in the early postoperative period. In each case, a clear view of the aqueous drainage tube was precluded. Occlusion of the end of the tube by iris tissue was demonstrated by UBM. An iridectomy over the tip of the tube instituted filtration in each case.
Interpretation: UBM was instrumental in diagnosing the presence and cause of occlusion of aqueous drainage tubes.