title: The correlation between cerebrospinal fluid pressure and retrolaminar tissue pressure.
abstract: OBJECTIVE
  To measure the effects of cerebrospinal fluid pressure (CSFp) on retrolaminar tissue pressure (RLTp) and the translaminar pressure gradient (TLPG), particularly at low CSFp, which is the normal situation in erect posture.
  
  
  METHODS
  Micropipettes coupled to a servonull pressure system were passed into eyes of anesthetized dogs to the optic disc and advanced in steps through the lamina cribrosa to the optic nerve subarachnoid space (ONSAS), while pressure measurements were taken. Cerebrospinal fluid pressure and intraocular pressure (IOP) were monitored and controlled. The TLPG was measured at varying IOPs and CSFps. The RLTp and ONSAS pressure (ONSASp) were measured at varying CSFps. In separate experiments, the optic nerve dura was incised, and pressure measurements were taken across the pia mater.
  
  
  RESULTS
  The TLPG was strongly correlated to the difference between IOP and CSFp (r=0.93; n=18) when CSFp was more than zero. Mean RLTp was 3.7+/-0.2 mm Hg (SEM; n=15) when CSFp was 0 mm Hg. The ONSASp and RLTp were largely dependent on the presence of CSFp higher than break point pressures of -0.5 mm Hg and 1.33 mm Hg, respectively. However, below these break points, RLTp (slope 0.07) and ONSASp (slope 0.18) were little influenced by CSFp. Separate measurements across the pia mater revealed that 95% of the pressure drop occurred within 100 microm of the pial surface.
  
  
  CONCLUSIONS
  The TLPG and RLTp are dependent on CSFp when CSFp is more than -0.5 mm Hg. Below this level, there is no hydrostatic continuity between the intracranial and optic nerve subarachnoid space. In this range, RLTp is stable and is little influenced by CSFp changes.
authors.affiliation: The Lions Eye Institute, Centre for Ophthalmology and Visual Science, University of Western Australia, Nedlands, Australia.
authors.forename: W H
authors.initials: WH
authors.lastname: Morgan
authors.forename: D Y
authors.initials: DY
authors.lastname: Yu
authors.forename: V A
authors.initials: VA
authors.lastname: Alder
authors.forename: S J
authors.initials: SJ
authors.lastname: Cringle
authors.forename: R L
authors.initials: RL
authors.lastname: Cooper
authors.forename: P H
authors.initials: PH
authors.lastname: House
authors.forename: I J
authors.initials: IJ
authors.lastname: Constable
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D015170:Cerebrospinal Fluid Pressure / Q000502:physiology*; D004285:Dogs; D007427:Intracranial Pressure / Q000502:physiology*; D007429:Intraocular Pressure / Q000502:physiology; D009898:Optic Disk / Q000098:blood supply / Q000502:physiology*; D009900:Optic Nerve / Q000502:physiology; D010841:Pia Mater / Q000502:physiology