title: Effects of changes in intraocular pressure on human ocular haemodynamics.
abstract: OBJECTIVE
  Myogenic autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. Ocular perfusion pressure is defined as the difference between ocular arterial pressure and ocular venous pressure, the latter dependent on intraocular pressure (IOP). The aim of the present study was to investigate the effect of moderate increases in IOP on ocular haemodynamics.
  
  
  METHODS
  Changes in IOP (+ 10 mmHg, +20 mmHg) were induced by a suction cup in 10 healthy subjects. Ocular fundus pulsations in the macula and the optic disc were measured by laser interferometry; blood flow velocities in the central retinal artery (CRA) and in the ophthalmic artery (OA) were measured by Doppler sonography.
  
  
  RESULTS
  Changes in IOP caused a significant reduction in fundus pulsations, which was more pronounced in the macula (at +10 mmHg: -9 +/- 2%, p < 0.01; at +20 mmHg: -19 +/- 3%, p < 0.001) than in the optic disc (at +10 mmHg: -5 +/- 2% (ns); at +20 mmHg: -9 +/- 3%, p < 0.01). Mean flow velocity in the CRA was reduced by -5 +/- 3% at +10 mmHg (ns) and by -14 +/- 5% at +20 mmHg (p < 0.005), resistive index was increased by +4 +/- 1% at +10 mmHg (p < 0.05) and by +6 +/- 2% at +20 mmHg (p < 0.01). In contrast, a rise in IOP did not affect blood flow parameters in the OA.
  
  
  CONCLUSIONS
  Our results from fundus pulsation measurements indicate that choroidal blood flow decreases when IOP is increased. The Doppler sonographic findings in the CRA indicate reduced blood flow velocity in this artery during raised IOP.
authors.affiliation: Department of Clinical Pharmacology, University of Vienna, Austria.
authors.forename: O
authors.initials: O
authors.lastname: Findl
authors.forename: K
authors.initials: K
authors.lastname: Strenn
authors.forename: M
authors.initials: M
authors.lastname: Wolzt
authors.forename: R
authors.initials: R
authors.lastname: Menapace
authors.forename: C
authors.initials: C
authors.lastname: Vass
authors.forename: H G
authors.initials: HG
authors.lastname: Eichler
authors.forename: L
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D002829:Choroid / Q000098:blood supply; D005260:Female; D005654:Fundus Oculi; D006706:Homeostasis; D006801:Humans; D007368:Interferometry; D007429:Intraocular Pressure; D008266:Macula Lutea / Q000098:blood supply*; D008297:Male; D009798:Ocular Hypertension / Q000503:physiopathology*; D009880:Ophthalmic Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D009898:Optic Disk / Q000098:blood supply*; D012161:Retinal Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D018608:Ultrasonography, Doppler