title: The dynamic response of intraocular pressure and ocular pulse amplitude to acute hemodynamic changes in normal and glaucomatous eyes.
abstract: OBJECTIVE
  To evaluate the effects of acute arterial blood pressure (ABP) and venous pressure changes on IOP in rats with experimental glaucoma.
  
  
  METHODS
  Unilateral experimental ocular hypertension was established in Sprague-Dawley rats by weekly intracameral injection of microbeads. Ocular pulse amplitude (OPA) and IOP were recorded from the anterior chamber using 1.2-Fr microsensors under urethane anesthesia. The effects on IOP during hemodynamic challenges using phenylephrine (PE) (50 μg/kg/min intravenous [IV]) and rapid saline loading (20 mL/kg/min IV) were studied.
  
  
  RESULTS
  Over an 8-week period, IOP was significantly elevated by 60% in the unilateral ocular hypertensive eyes. Both ABP and IOP were significantly increased by PE infusion. A significantly greater IOP increase was found in the experimental eyes compared with control eyes (1.32 ± 0.18 mm Hg vs. 0.90 ± 0.09 mm Hg). Correspondingly, higher OPAs and an amplification of the OPA during arterial hypertension were found in the experimental eyes. A sustained rise in IOP secondary to IV saline loading was observed, with a greater rise observed among experimental eyes (0.74 ± 0.13 mm Hg vs. 0.37 ± 0.005 mm Hg).
  
  
  CONCLUSIONS
  Sympathetic acceleration of ABP using PE resulted in surges in IOP and OPA. In contrast, increased venous pressure resulted in a more sustained rise in IOP but to a lesser extent. These responses were more pronounced in eyes with experimental glaucoma compared with control eyes, which may reflect the higher starting IOP contributing to a reduced ocular compliance. Our results suggest that eyes with ocular hypertension are more susceptible to IOP variability induced by hemodynamic fluctuations.
authors.affiliation: Department of Ophthalmology, Australian School of Advanced Medicine, Macquarie University, North Ryde, New South Wales, Australia.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Li
authors.forename: Vivek K
authors.initials: VK
authors.lastname: Gupta
authors.forename: Yuyi
authors.initials: Y
authors.lastname: You
authors.forename: Keith W
authors.initials: KW
authors.lastname: Ng
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Graham
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D062186:Arterial Pressure / Q000502:physiology*; D004195:Disease Models, Animal; D005901:Glaucoma / Q000503:physiopathology*; D006439:Hemodynamics; D007429:Intraocular Pressure / Q000502:physiology*; D009798:Ocular Hypertension / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014690:Venous Pressure / Q000502:physiology*
keywords: blood pressure; intraocular pressure; ocular hypertension; ocular pulse amplitude; phenylephrine