title: Evaluation of the effect of elevated intraocular pressure and reduced ocular perfusion pressure on retinal capillary bed filling and total retinal blood flow in rats by OMAG/OCT.
abstract: OBJECTIVE
  To determine if retinal capillary filling is preserved in the face of acutely elevated intraocular pressure (IOP) in anesthetized rats, despite a reduction in total retinal blood flow (RBF), using optical microangiography/optical coherence tomography (OMAG/OCT).
  
  
  METHODS
  OMAG provided the capability of depth-resolved imaging of the retinal microvasculature down to the capillary level. Doppler OCT was applied to measure the total RBF using an enface integration approach. The microvascular pattern, capillary density, and total RBF were monitored in vivo as the IOP was increased from 10 to 100mmHg in 10mmHg intervals and returned back to 10mmHg.
  
  
  RESULTS
  In animals with mean arterial pressure (MAP) of 102±4mmHg (n=10), when IOP was increased from 0 to 100mmHg, the capillary density remained at or above 80% of baseline for the IOP up to 60mmHg [or ocular perfusion pressure (OPP) at 40mmHg]. This was then decreased, achieving 60% of baseline at IOP 70mmHg and OPP of 30mmHg. Total RBF was unaffected by moderate increases in IOP up to 30mmHg, beyond which total RBF decreased linearly, reaching 50% of baseline at IOP 60mmHg and OPP 40mmHg. Both capillary density and total RBF were totally extinguished at 100mmHg, but fully recovered when IOP returned to baseline. By comparison, a separate group of animals with lower MAP (mean=75±6mmHg, n=7) demonstrated comparable decreases in both capillary filling and total RBF at IOPs that were 20mmHg lower than in the initial group. Both were totally extinguished at 80mmHg, but fully recovered when IOP returned to baseline. Relationships of both parameters to OPP were unchanged.
  
  
  CONCLUSIONS
  Retinal capillary filling and total RBF responses to IOP elevation can be monitored non-invasively by OMAG/OCT and both are influenced by OPP. Retinal capillary filling was relatively preserved down to a perfusion pressure of 40mmHg, despite a linear reduction in total RBF.
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, WA 98195, USA.
authors.forename: Zhongwei
authors.initials: Z
authors.lastname: Zhi
authors.affiliation: Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA.
authors.forename: William
authors.initials: W
authors.lastname: Cepurna
authors.affiliation: Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA.
authors.forename: Elaine
authors.initials: E
authors.lastname: Johnson
authors.affiliation: Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA.
authors.forename: Hari
authors.initials: H
authors.lastname: Jayaram
authors.affiliation: Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA.
authors.forename: John
authors.initials: J
authors.lastname: Morrison
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, WA 98195, USA; Department of Ophthalmology, University of Washington, Seattle, WA 98195, USA. Electronic address: wangrk@uw.edu.
authors.forename: Ruikang K
authors.initials: RK
authors.lastname: Wang
mesh_terms: D000792:Angiography; D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002196:Capillaries; D003287:Contrast Media / Q000737:chemistry; D004867:Equipment Design; D021621:Imaging, Three-Dimensional; D007429:Intraocular Pressure; D008833:Microcirculation; D010477:Perfusion; D011312:Pressure; D051381:Rats; D012039:Regional Blood Flow / Q000502:physiology*; D012160:Retina / Q000473:pathology*; D012171:Retinal Vessels / Q000473:pathology*; D041623:Tomography, Optical Coherence
chemical_list: D003287:Contrast Media
keywords: Intra-ocular pressure; Medical and biological imaging; Optical coherence tomography; Optical microangiography; Retinal blood flow