title: Mapping the surface astrocytes of the optic disc: a fluid-conducting role of the astrocytic covering of the central vessels.
abstract: BACKGROUND
  The vitreous interface of the optic nerve has been studied to delimit the covering of Elschnig's astrocytes and interstitial pathways of flow through the prelaminar region.
  
  
  METHODS
  Perfusion of the prelaminar tissue under controlled pressure with a fluorescent marker injected into the vitreous cavity in pig eyes. The prelaminar region of the optic nerve and adjacent retina was fixed and flatmounted or frozen and cryosectioned and examined with the confocal laser microscope. Samples were also prepared for conventional transmission electron microscopy.
  
  
  RESULTS
  The surface of the vitreous surface of the optic nerve is covered by a cobblestone-like pavement made of astrocytic projections. Intensely stained passages of different thickness indicate the presence of wide interconnected intercellular spaces in the covering of Elschnig's astrocytes. Those passages are absent in the intervascular areas occupied by axons and axon-linked astrocytes.
  
  
  CONCLUSIONS
  Delineation of the astrocytic pavement and the preferred flow routes formed by wide extracellular spaces are conspicuous features of the prelaminar region when examined with the confocal laser microscope and the help of sticky fluorescent tracer. This suggests that excess extracellular fluid can be interchanged with the vitreous by a network of interconnected extracellular spaces or preferred flow routes. Some pathogenic mechanisms can be related to fluid interchange in the optic nerve head.
authors.affiliation: Department of Surgery (Ophthalmology), Faculty of Medicine, University of Granada, Av. de Madrid 11, Granada 18012, Spain. fjcarreras@telefonica.net
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Carreras
authors.forename: David
authors.initials: D
authors.lastname: Porcel
authors.forename: Jose I
authors.initials: JI
authors.lastname: Muñoz-Avila
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology* / Q000648:ultrastructure; D018613:Microscopy, Confocal / Q000379:methods; D008854:Microscopy, Electron; D009898:Optic Disk / Q000033:anatomy & histology* / Q000648:ultrastructure; D009900:Optic Nerve / Q000033:anatomy & histology / Q000166:cytology / Q000648:ultrastructure; D012160:Retina / Q000033:anatomy & histology / Q000166:cytology / Q000648:ultrastructure; D012171:Retinal Vessels / Q000033:anatomy & histology* / Q000166:cytology / Q000648:ultrastructure; D013552:Swine; D014822:Vitreous Body / Q000166:cytology / Q000648:ultrastructure