title: Location of glaucoma drainage devices relative to the optic nerve.
abstract: BACKGROUND
  Limited data are available to guide optimal positioning of glaucoma drainage devices (GDD) in relation to the limbus and optic nerve. The authors aim to provide guidelines for appropriate and safe GDD implantation.
  
  
  METHODS
  The optimal positioning of five different GDD were evaluated using necropsy eyes of varying axial lengths. The dependent variable that was measured was the maximum distance that a GDD could be placed posterior to the limbus while remaining 2 mm away from the optic nerve.
  
  
  RESULTS
  The average maximum distance posterior to the limbus of the anterior plate edge ranged between 9.0-15.0 mm in the superotemporal quadrant for the GDD tested. The distances for superonasal, inferonasal, and inferotemporal quadrants ranged between 8.0-14.0 mm, 9.0-14.0 mm, and 11.0-17.0 mm, respectively. The Molteno device could be placed most posteriorly while remaining 2 mm away from the nerve. The Ahmed FP7 and S2 were the least amenable to posterior placement before encroaching on the 2 mm limit.
  
  
  CONCLUSIONS
  The maximum distance that a GDD can be placed posterior to the limbus, before encroachment around the optic nerve, varies between different devices and quadrants of placement. Taking a measurement of the exact distance of the plate from the limbus during GDD surgery is recommended.
authors.affiliation: UPMC Eye Center, Eye and Ear Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA. malik.kahook@gmail.com
authors.forename: M Y
authors.initials: MY
authors.lastname: Kahook
authors.forename: R J
authors.initials: RJ
authors.lastname: Noecker
authors.forename: M B
authors.initials: MB
authors.lastname: Pantcheva
authors.forename: J S
authors.initials: JS
authors.lastname: Schuman
mesh_terms: D005123:Eye / Q000033:anatomy & histology; D020327:Glaucoma Drainage Implants; D006801:Humans; D018465:Molteno Implants; D009900:Optic Nerve / Q000033:anatomy & histology*; D011474:Prosthesis Design; D019919:Prosthesis Implantation / Q000379:methods