title: Use of ultrasound biomicroscopy to diagnose Ahmed valve obstruction by iris.
abstract: 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.
  
  
  CONCLUSIONS
  UBM was instrumental in diagnosing the presence and cause of occlusion of aqueous drainage tubes.
authors.affiliation: Department of Ophthalmology, Toronto Western Hospital, Ont.
authors.forename: Monica M
authors.initials: MM
authors.lastname: Carrillo
authors.forename: Graham E
authors.initials: GE
authors.lastname: Trope
authors.forename: Charles
authors.initials: C
authors.lastname: Pavlin
authors.forename: Yvonne M
authors.initials: YM
authors.lastname: Buys
mesh_terms: D000328:Adult; D000368:Aged; D000867:Anterior Chamber / Q000000981:diagnostic imaging / Q000601:surgery; D000959:Antihypertensive Agents / Q000627:therapeutic use; D002924:Ciliary Body / Q000000981:diagnostic imaging / Q000601:surgery; D005260:Female; D005901:Glaucoma / Q000601:surgery; D020327:Glaucoma Drainage Implants / Q000009:adverse effects*; D006801:Humans; D007429:Intraocular Pressure; D032801:Iridectomy; D007498:Iris / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D008297:Male; D033401:Microscopy, Acoustic; D011183:Postoperative Complications; D011475:Prosthesis Failure
chemical_list: D000959:Antihypertensive Agents