title: Intracranial pressure (ICP) and optic nerve subarachnoid space pressure (ONSP) correlation in the optic nerve chamber: the Beijing Intracranial and Intraocular Pressure (iCOP) study.
abstract: OBJECTIVE
  Because a lowered intracranial pressure (ICP) is a possible mechanism of optic neuropathy, we wished to study the CSF dynamics in the optic nerve chamber by recording possible changes in the optic nerve subarachnoid space pressure (ONSP) and the impact on it when acutely lowering ICP.
  
  
  METHODS
  In eight normal dogs pressure probes were implanted in the left brain ventricle, lumbar cistern, optic nerve subarachnoid space and in the anterior eye chamber. Following CSF shunting from the brain ventricle we monitored changes of ICP, lumbar cistern pressure (LCP), ONSP and intraocular pressure (IOP).
  
  
  RESULTS
  At baseline, the pressures were different with ICP>LCP>ONSP but correlated with each other (P<0.001). The "trans-lamina cribrosa pressure gradient" (TLPG) was highest for IOP-ONSP, lower for IOP-LCP, and lowest for IOP-ICP (P<0.001). During CSF shunting the ICP gradually decreased in a linear fashion together with the ONSP ("ICP-depended zone"). But when the ICP fell below a critical breakpoint, ICP and ONSP became uncoupled and ONSP remained constant despite further ICP decline ("ICP-independent zone").
  
  
  CONCLUSIONS
  Because the parallel decline of ICP and ONSP breaks down when ICP decreases below a critical breakpoint, we interpret this as a sign of CSF communication arrest between the intracranial and optic nerve SAS. This may be caused by obstructions of either CSF inflow through the optic canal or outflow into the intra-orbital cavity. This CSF exchange arrest may be a contributing factor to optic nerve damage and the optic nerve chamber syndrome which may influence the loss of vision or its restoration.
authors.affiliation: Department of Neurosurgery, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
authors.forename: Ruowu
authors.initials: R
authors.lastname: Hou
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China; Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
authors.forename: Diya
authors.initials: D
authors.lastname: Yang
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China; Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
authors.forename: Huaizhou
authors.initials: H
authors.lastname: Wang
authors.affiliation: Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Ophthalmology, Xuanwu Hospital, Capital Medical University, Beijing, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Li
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China.
authors.forename: Jinghong
authors.initials: J
authors.lastname: Sang
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China.
authors.forename: Sumeng
authors.initials: S
authors.lastname: Liu
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China.
authors.forename: Yiwen
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Department of Ophthalmology, Eye Hospital of China Academy of Chinese Medical Sciences, Beijing, China.
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Xie
authors.affiliation: Eye center, New York Eye and Ear Infirmary, NY, USA.
authors.forename: Ruojin
authors.initials: R
authors.lastname: Ren
authors.affiliation: Department of Endoscopic and Microinvasive Neurosugery, Beijing Neurosurgery Institute, Beijing Tiantian Hospital, Capital Medical University, Beijing, China. Electronic address: zyz2004520@163.com.
authors.forename: Yazhuo
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Institute of Medical Psychology, Medical Faculty, Otto-v.-Guericke University of Magdeburg, Magdeburg, Germany.
authors.forename: Bernhard A
authors.initials: BA
authors.lastname: Sabel
authors.affiliation: Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China; Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China. Electronic address: wningli@vip.163.com.
authors.forename: Ningli
authors.initials: N
authors.lastname: Wang
mesh_terms: D000818:Animals; D000068476:Beijing; D004285:Dogs; D057446:Hydrodynamics; D007427:Intracranial Pressure; D007429:Intraocular Pressure / Q000502:physiology*; D009900:Optic Nerve / Q000502:physiology*; D013346:Subarachnoid Space / Q000502:physiology*
keywords: Cerebrospinal fluid dynamics; Glaucoma; Optic nerve chamber; Optic nerve subarachnoid space pressure (ONSP); Optic neuropathy; Trans-optic canal pressure gradient (TCPG)