title: A model to measure fluid outflow in rabbit capsules post glaucoma implant surgery.
abstract: OBJECTIVE
  Prior models of glaucoma filtration surgery assess bleb morphology, which does not always reflect function. Our aim is to establish a model that directly measures tissue hydraulic conductivity of postsurgical outflow in rabbit bleb capsules following experimental glaucoma filtration surgery.
  
  
  METHODS
  Nine rabbits underwent insertion of a single-plate pediatric Molteno implant into the anterior chamber of their left eye. Right eyes were used as controls. The rabbits were then allocated to one of two groups. Group one had outflow measurements performed at 1 week after surgery (n = 5), and group two had measurements performed at 4 weeks (n = 4). Measurements were performed by cannulating the drainage tube ostium in situ with a needle attached to a pressure transducer and a fluid column at 15 mm Hg. The drop in the fluid column was measured every minute for 5 minutes. For the control eyes (n = 6), the anterior chamber of the unoperated fellow eye was cannulated. Animals were euthanized with the implant and its surrounding capsule dissected and fixed in 4% paraformaldehyde, and embedded in paraffin before 6-μm sections were cut for histologic staining.
  
  
  RESULTS
  By 7 days after surgery, tube outflow was 0.117 ± 0.036 μL/min/mm Hg at 15 mm Hg (mean ± SEM), whereas at 28 days, it was 0.009 ± 0.003 μL/min/mm Hg. Control eyes had an outflow of 0.136 ± 0.007 μL/min/mm Hg (P = 0.004, one-way ANOVA). Hematoxylin and eosin staining demonstrated a thinner and looser arrangement of collagenous tissue in the capsules at 1 week compared with that at 4 weeks, which had thicker and more densely arranged collagen.
  
  
  CONCLUSIONS
  We describe a new model to directly measure hydraulic conductivity in a rabbit glaucoma surgery implant model. The principal physiologic endpoint of glaucoma surgery can be reliably quantified and consistently measured with this model. At 28 days post glaucoma filtration surgery, a rabbit bleb capsule has significantly reduced tissue hydraulic conductivity, in line with loss of implant outflow facility, and increased thickness and density of fibrous encapsulation.
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
authors.forename: Dan Q
authors.initials: DQ
authors.lastname: Nguyen
authors.forename: Craig M
authors.initials: CM
authors.lastname: Ross
authors.forename: Yu Qin
authors.initials: YQ
authors.lastname: Li
authors.forename: Surinder
authors.initials: S
authors.lastname: Pandav
authors.forename: Bruce
authors.initials: B
authors.lastname: Gardiner
authors.forename: David
authors.initials: D
authors.lastname: Smith
authors.forename: Alicia C
authors.initials: AC
authors.lastname: How
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Crowston
authors.forename: Michael A
authors.initials: MA
authors.lastname: Coote
mesh_terms: D000818:Animals; D000867:Anterior Chamber / Q000473:pathology / Q000601:surgery*; D001082:Aqueous Humor / Q000502:physiology*; D004195:Disease Models, Animal; D005260:Female; D005901:Glaucoma / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D007429:Intraocular Pressure / Q000502:physiology; D018465:Molteno Implants; D019919:Prosthesis Implantation; D011817:Rabbits; D014065:Tonometry, Ocular