title: Outflow characteristics of isolated anterior segments of human eyes.
abstract: OBJECTIVE
  To evaluate the relationship between intraocular pressure (IOP) and flow through the trabecular meshwork in isolated anterior segments of human eyes. Outflow facility (C) is thought to decrease proportionally with increasing IOP in human eyes in vivo and in vitro.
  
  
  METHODS
  Twenty-nine eviscerated human anterior segments were perfused with ascending and descending pressure sequences in a stepwise fashion (range, 4 to 40 mm Hg); 11 of the 29 eyes were treated similarly after 20 hours of perfusion at 12 mm Hg. Pressure-flow sequences of individual eyes were evaluated with a linear (constant C) and a nonlinear regression method (C decreasing with increasing IOP). In addition, in eight intact postmortem eyes, pressure-flow characteristics were determined, followed by perfusion of their isolated anterior segments.
  
  
  RESULTS
  Pressure-flow sequences as determined by linear regression had an average correlation coefficient of 0.99. Average C (slope of the plot) was 0.26 +/- 0.03 microliter minute-1 mm Hg-1. There was no influence of direction of pressure sequence or time on C. To test for linearity, the hypothetical outflow obstruction coefficient (Q) was determined for each plot. Median Q of 29 eyes was 0.003 mm Hg-1, and in 45% (13 eyes) Q was negative, suggesting facilitation instead of obstruction. This indicates that the outflow obstruction coefficient is not a physiological parameter in isolated anterior segments.
  
  
  CONCLUSIONS
  The relationship between IOP and flow through perfused isolated anterior segments of human eyes is linear between 4 and 40 mm Hg, indicating that within this range outflow facility is constant and does not decrease with increasing IOP.
authors.affiliation: Department of Experimental Ophthalmology, The Netherlands Ophthalmic Research Institute, Amsterdam, The Netherlands.
authors.forename: B G
authors.initials: BG
authors.lastname: Dijkstra
authors.forename: J M
authors.initials: JM
authors.lastname: Ruijter
authors.forename: P F
authors.initials: PF
authors.lastname: Hoyng
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000869:Anterior Eye Segment / Q000502:physiology*; D001082:Aqueous Humor / Q000502:physiology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008875:Middle Aged; D009924:Organ Culture Techniques; D010477:Perfusion; D012044:Regression Analysis; D014129:Trabecular Meshwork / Q000502:physiology