title: Effect of a nifedipine induced reduction in blood pressure on the association between ocular pulse amplitude and ocular fundus pulsation amplitude in systemic hypertension.
abstract: BACKGROUND
  The ocular pressure/volume relation, which is described by the Friedenwald equation, forms the basis of intraocular pressure (IOP) measurement with Schiotz tonometry and measurement of pulsatile ocular blood flow (POBF) with pneumotonometry. Changes in intraocular volume during the cardiac cycle are caused by arterial inflow and venous outflow and are accompanied by changes in IOP. The relation between volume and pressure changes is dependent on the elastic properties of the eye coats as described by the ocular rigidity coefficient. Previous studies indicate that there is a vascular contribution to ocular rigidity and that the volume/pressure relationship may depend on the mean arterial pressure.
  
  
  METHODS
  The effect of a nifedipine induced reduction in systemic blood pressure on pulse amplitude (PA) as assessed with pneumotonometry and fundus pulsation amplitude (FPA), as measured with laser interferometry was investigated in 16 untreated patients with moderate to severe systemic hypertension (mean arterial pressure 123 (SD 12) mm Hg).
  
  
  RESULTS
  The ratio between PA and FPA was taken as a measure of the ocular rigidity coefficient. Nifedipine reduced mean arterial pressure by 17.3% and increased pulse rate by 11.0% (p<0.001 each). Whereas PA was significantly reduced after administration of nifedipine (-15.6%; p<0.001), FPA remained unchanged. Accordingly, the ratio of PA/FPA was reduced from 0.86 mm Hg/mum to 0.73 mm Hg/mum after administration of nifedipine.
  
  
  CONCLUSIONS
  These data are in keeping with previous animal experiments indicating a blood pressure dependent vascular component to the rigidity of the eye coats in vivo. This needs to be taken into account for measurement of IOP with Schiotz tonometry and POBF with pneumotonometry.
authors.affiliation: Department of Clinical Pharmacology, Medical University of Austria, Währinger Gürtel 18-20, A-1090 Vienna, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Bayerle-Eder
authors.forename: J
authors.initials: J
authors.lastname: Kolodjaschna
authors.forename: M
authors.initials: M
authors.lastname: Wolzt
authors.forename: E
authors.initials: E
authors.lastname: Polska
authors.forename: S
authors.initials: S
authors.lastname: Gasic
authors.forename: L
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000368:Aged; D001794:Blood Pressure / Q000187:drug effects; D004548:Elasticity / Q000187:drug effects; D005123:Eye / Q000098:blood supply / Q000187:drug effects* / Q000503:physiopathology; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006973:Hypertension / Q000188:drug therapy* / Q000503:physiopathology; D007429:Intraocular Pressure / Q000187:drug effects; D007834:Lasers; D008297:Male; D008875:Middle Aged; D009543:Nifedipine / Q000494:pharmacology*; D011673:Pulsatile Flow / Q000187:drug effects; D012171:Retinal Vessels / Q000187:drug effects* / Q000503:physiopathology; D014065:Tonometry, Ocular; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D014665:Vasodilator Agents; D009543:Nifedipine