title: Pathophysiology of and prophylaxis against late ahmed glaucoma valve occlusion.
abstract: OBJECTIVE
  To understand the pathophysiology of late Ahmed Glaucoma Valve failures and devise strategies to minimize this problem.
  
  
  METHODS
  One hundred sixty eyes that had undergone Ahmed Glaucoma Valve implants by one surgeon were retrospectively reviewed. Six eyes with late (greater than 3 months) Ahmed Glaucoma Valve occlusion requiring operative intervention were identified. Two of these eyes underwent initial successful transcameral drainage tube irrigation and four initially required Ahmed Glaucoma Valve exchange. Intraoperative images, postoperative histologic analysis, and Ahmed Glaucoma Valve handling experiments were performed.
  
  
  RESULTS
  Two eyes with late occlusion (33%; 1.25% of total implants) were initially successfully treated with irrigation alone. A gap between the valve cover and valve body junction allowed fibrovascular ingrowth and produced valve failure ultimately in five of six eyes (83%; 3.1% of total implants). This gap could be produced by grasping the device along the center line, indenting the valve cover, and damaging the plastic rivets attaching the valve cover to the valve body. Handling the Ahmed Glaucoma Valve outside this "no touch zone" eliminated this problem.
  
  
  CONCLUSIONS
  Leaflet adhesion has a low incidence and may be treated by transcameral drainage tube irrigation. Late onset distal occlusion is best treated by Ahmed Glaucoma Valve exchange with respect for the "no touch zone." Respecting the "no touch zone over the valve mechanism should avoid creation of gaps between the valve cover and valve body junction, which allow secondary fibrovascular ingrowth.
authors.affiliation: Departments of Ophthalmology, University of California, Irvine, California 92697-4375, USA. rahill@uci.edu
authors.forename: R A
authors.initials: RA
authors.lastname: Hill
authors.forename: A
authors.initials: A
authors.lastname: Pirouzian
authors.forename: L
authors.initials: L
authors.lastname: Liaw
mesh_terms: D001082:Aqueous Humor / Q000378:metabolism; D020878:Device Removal; D004322:Drainage / Q000379:methods; D005901:Glaucoma / Q000503:physiopathology* / Q000601:surgery; D020327:Glaucoma Drainage Implants / Q000009:adverse effects*; D006801:Humans; D007429:Intraocular Pressure; D011183:Postoperative Complications / Q000503:physiopathology* / Q000517:prevention & control*; D011475:Prosthesis Failure; D012086:Reoperation; D012189:Retrospective Studies