title: In vitro flow characteristics of the Ahmed and self-constructed anterior chamber shunts.
abstract: OBJECTIVE
  To compare in vitro opening pressures (OP) and closing pressures (CP) of the Ahmed VS-1 and VS-2 glaucoma valves with those of several self-constructed valve 'prototypes,' and to assess their ability to maintain perfusion pressures between 6 and 21 mm of Hg.
  
  
  METHODS
  Ahmed VS-1 (n = 6), 2 groups of Ahmed VS-2 (group 1: n = 12; group 2: n = 14), and self-constructed valves with linear incisions in the long axis of the tube wall (n = 6) or X-shaped incisions in the tube walls (n = 2).
  
  
  METHODS
  Valves were perfused with deionized water, lactated Ringer's solution (LRS), Dulbecco's modified Eagle's medium (DMEM), DMEM plus 50% equine serum (ES), and 100% ES. Flow rates of 2.85, 4.2, 6.0, 9.0, and 12.0 microliter/min were used for each perfusate. Valves were tested 3 times for reproducibility, and OP/CP were compared for each system.
  
  
  RESULTS
  OP/CP of the VS-1, VS-2 (group 1), VS-2 (group 2), and linear 1.0-cm incisional valves with thick tubing consistently increased with increasing perfusion rate. Linear 0.5-cm (thick tubing) and 1.0-cm (thin tubing) incisional valves had increasing OP/CP with increasing perfusion rate in all but a few instances. Mean OP/CP decreased with increasing perfusate osmolarity for all perfusates except LRS, using the VS-1 and V-2 (group 2) valves. Mean OP/CP were consistently lower for VS-1 than VS-2 (group 1) valves at any given flow rate and for any given perfusate. Mean OP/CP were consistently lower for VS-2 (group 1) than VS-2 (group 2) valves at any given flow rate and for any given perfusate. The linear 0.5-cm incisional valves with thick and thin tubing induced the highest mean OP/CP, maximizing at > 30 mm of Hg.
  
  
  CONCLUSIONS
  Only the VS-2 (group 2) valves consistently had mean OP/CP between 6 and 21 mm of Hg for all perfusates and at all flow rates.
  
  
  CONCLUSIONS
  Anterior chamber shunts, although imperfect, appear to offer a physiologically sound alternative for glaucoma management.
authors.affiliation: Gwathmey-Adams Laboratory for Visual Science, College of Veterinary Medicine, University of Florida, Gainesville 32610-0126, USA.
authors.forename: D T
authors.initials: DT
authors.lastname: Strubbe
authors.forename: K N
authors.initials: KN
authors.lastname: Gelatt
authors.forename: E O
authors.initials: EO
authors.lastname: MacKay
mesh_terms: D000818:Animals; D000867:Anterior Chamber / Q000473:pathology / Q000601:surgery*; D004283:Dog Diseases / Q000503:physiopathology / Q000601:surgery; D004285:Dogs; D004867:Equipment Design; D005069:Evaluation Studies as Topic; D005901:Glaucoma / Q000503:physiopathology / Q000601:surgery / Q000662:veterinary; D007429:Intraocular Pressure / Q000502:physiology; D018465:Molteno Implants / Q000662:veterinary*; D009994:Osmolar Concentration; D010477:Perfusion / Q000295:instrumentation / Q000379:methods / Q000662:veterinary; D015203:Reproducibility of Results