title: Ocular rigidity, ocular pulse amplitude, and pulsatile ocular blood flow: the effect of intraocular pressure.
abstract: OBJECTIVE
  The purpose of this study was to characterize the pressure-volume relation in the living human eye, measure the ocular pulse amplitude (OPA), and calculate the corresponding pulsatile ocular blood flow (POBF) in a range of clinically relevant IOP levels.
  
  
  METHODS
  Fifty patients with cataract (50 eyes) were enrolled in the study. After cannulation of the anterior chamber, a computer-controlled device for the intraoperative measurement and control of IOP was used to artificially increase the IOP in a stepping procedure from 15 to 40 mm Hg. The IOP was continuously recorded for 2 seconds after each infusion step. The pressure-volume relation was approximated with an exponential fit, and the ocular rigidity coefficient was computed. OPA, pulse volume (PV), and POBF were measured from the continuous IOP recordings.
  
  
  RESULTS
  The average rigidity coefficient was 0.0224 microL(-1) (SD 0.0049). OPA increased by 91% and PV and POBF decreased by 29% and 30%, respectively, when increasing the IOP from 15 to 40 mm Hg. The OPA is positively correlated with the coefficient of ocular rigidity (r = 0.65, P < 0.01).
  
  
  CONCLUSIONS
  The present results suggest a nonlinear pressure-volume relation in the living human eye characterized by an increase in rigidity at higher IOP levels. The increased OPA and decreased pulse volume relate to the decreased POBF and the increased mechanical resistance of the ocular wall at high IOP levels.
authors.affiliation: Institute of Optics and Vision, Medical School, University of Crete, Voutes, Greece. anna.dastiridou@gmail.com
authors.forename: Anna I
authors.initials: AI
authors.lastname: Dastiridou
authors.forename: Harilaos S
authors.initials: HS
authors.lastname: Ginis
authors.forename: Dirk
authors.initials: D
authors.lastname: De Brouwere
authors.forename: Miltiadis K
authors.initials: MK
authors.lastname: Tsilimbaris
authors.forename: Ioannis G
authors.initials: IG
authors.lastname: Pallikaris
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001794:Blood Pressure / Q000502:physiology*; D004547:Elastic Tissue / Q000502:physiology*; D005123:Eye / Q000098:blood supply*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012039:Regional Blood Flow / Q000502:physiology; D014065:Tonometry, Ocular