title: Intraluminal pressure response in Baerveldt tube shunts: a comparison of modification techniques.
abstract: OBJECTIVE
  To design an apparatus for in vitro quantification of effects of modifications to nonvalved tube shunts, and to compare the effects of these modifications done to prevent early postoperative hypotony.
  
  
  METHODS
  A testing apparatus was designed and constructed to measure intraluminal pressure (ILP) during constant infusion of balanced salt solution at 2 microL/min through Baerveldt tube shunts mounted on cadaver eyes. Three different modifications were performed and 3 shunts were used for each modification. The modifications were partial tube occlusion with a 3-0 Supramid suture, tube perforation with a 27-gauge needle on an occluded tube, and a 1.2 mm longitudinal venting slit on an occluded tube.
  
  
  RESULTS
  The final steady state ILP for the 3-0 Supramid partially occluded tube ranged between 1.6 and 2.8 mm Hg over 3 trials with an average final steady state ILP of 2.0 mm Hg. The 27-gauge needle perforation produced ILPs of 4.6 to 8.2 mm Hg over 3 trials with an average final steady state pressure of 5.9 mm Hg. The 1.2 mm longitudinal venting slit produced an ILP range of 12.6 to 17.3 mm Hg over 3 trials with an average final steady state ILP of 14.8 mm Hg. The differences in final steady state ILP between the 3 modification techniques were statistically significant (P=0.00036).
  
  
  CONCLUSIONS
  The 3-0 Supramid occlusion and the 27-gauge perforation techniques produced hypotony, whereas the 1.2 mm longitudinal venting slit produced acceptable pressures in vitro.
authors.affiliation: Wake Forest University Eye Center, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1033, USA.
authors.forename: David D
authors.initials: DD
authors.lastname: Gilbert
authors.forename: Brent
authors.initials: B
authors.lastname: Bond
mesh_terms: D001082:Aqueous Humor / Q000378:metabolism; D004867:Equipment Design; D020327:Glaucoma Drainage Implants; D006801:Humans; D007260:Infusion Pumps; D007429:Intraocular Pressure / Q000502:physiology*; D015814:Ocular Hypotension / Q000517:prevention & control; D011183:Postoperative Complications / Q000517:prevention & control; D011312:Pressure; D013536:Suture Techniques