title: Manometric measurement of the outflow facility in the living human eye and its dependence on intraocular pressure.
abstract: OBJECTIVE
  The intraocular pressure (IOP) is determined by a dynamic equilibrium between the production and outflow of the aqueous humour. The relationship between IOP and the outflow rate through the conventional and unconventional pathway is quantified by the outflow facility coefficient (C). The purpose of this study is to employ a direct (manometric) tonographic technique and determine C as well as its inverse, resistance (R), as a function of IOP in the living human eye.
  
  
  METHODS
  Nineteen cataract patients were enrolled in the study. An intraoperative manometric device was used to measure IOP. After cannulation of the anterior chamber, the IOP was increased by infusion of controlled amounts of saline solution. At 40 mmHg, the infusion stopped, and a pressure sensor recorded the IOP. The measured pressure-volume relationship was considered in order to convert pressure changes to corresponding ocular volume changes. An appropriate mathematical model was applied to calculate C and (its inverse), R.
  
  
  RESULTS
  The average C was 0.0672 ± 0.0296 μl/min/mmHg at 40 mmHg and 0.2652 ± 0.1164 μl/min/mmHg at 20 mmHg. There was a strong dependence of coefficient C on IOP in all subjects (p < 0.001). The corresponding values for R were 17.9 ± 11.17 min mmHg/μl at 40 mmHg and 4.51 ± 2.69 min mmHg/μl at 20 mmHg.
  
  
  CONCLUSIONS
  This study provides measurement of outflow facility and its dependence with pressure in healthy living human eyes. This relation is shown to be non-linear, using a direct manometric method.
authors: Medical School, Institute of Vision and Optics, University of Crete, Heraklion, Greece.
authors: Nikolaos G
authors: http://orcid.org/0000-0001-9060-9538
authors: NG
authors: Karyotakis
authors: Medical School, Institute of Vision and Optics, University of Crete, Heraklion, Greece.
authors: Harilaos S
authors: HS
authors: Ginis
authors: Opththalmology Department, University Hospital of Larissa, Larissa, Greece.
authors: Anna I
authors: AI
authors: Dastiridou
authors: Medical School, Institute of Vision and Optics, University of Crete, Heraklion, Greece.|Opththalmology Department, University Hospital of Heraklion, Heraklion, Greece.
authors: Miltiadis K
authors: MK
authors: Tsilimbaris
authors: Medical School, Institute of Vision and Optics, University of Crete, Heraklion, Greece.|Opththalmology Department, University Hospital of Heraklion, Heraklion, Greece.
authors: Ioannis G
authors: IG
authors: Pallikaris
mesh_terms: D000368:Aged; D001082:Aqueous Humor / Q000502:physiology*; D058452:Axial Length, Eye; D004548:Elasticity / Q000502:physiology; D005260:Female; D006801:Humans; D057446:Hydrodynamics; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008962:Models, Theoretical; D014065:Tonometry, Ocular / Q000295:instrumentation*; D014129:Trabecular Meshwork / Q000378:metabolism*
keywords: humour dynamics; intraocular pressure; outflow facility; resistance to outflow; rigidity
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