title: Evaluation of the Zeiss retinal vessel analyser.
abstract: OBJECTIVE
  To investigate the reproducibility and sensitivity of the Zeiss retinal vessel analyser, a new method for the online determination of retinal vessel diameters in healthy subjects.
  
  
  METHODS
  Two model drugs were administered, a peripheral vasoconstrictor (the alpha receptor agonist phenylephrine) and a peripheral vasodilator (the nitric oxide donor sodium nitroprusside) in stepwise increasing doses. Nine healthy young subjects were studied in a placebo controlled double masked three way crossover design. Subjects received intravenous infusions of either placebo or stepwise increasing doses of phenylephrine (0.5, 1, or 2 microg/kg/min) or sodium nitroprusside (0.5, 1, or 2 microg/kg/min). Retinal vessel diameters were measured with the new Zeiss retinal vessel analyser. Retinal leucocyte velocity, flow, and density were measured with the blue field entoptic technique. The reproducibility of measurements was assessed with coefficients of variation and intraclass correlation coefficients.
  
  
  RESULTS
  Placebo and phenylephrine did not influence retinal haemodynamics, although the alpha receptor antagonist significantly increased blood pressure. Sodium nitroprusside induced a significant increase in retinal venous and arterial diameters (p<0.001 each), leucocyte density (p=0.001), and leucocyte flow (p=0.024) despite lowering blood pressure to a significant degree. For venous and arterial vessel size measurements short term coefficients of variation were 1.3% and 2.6% and intraclass correlation coefficients were 0.98 and 0.96, respectively. The sensitivity was between 3% and 5% for retinal veins and 5% and 7% for retinal arteries.
  
  
  CONCLUSIONS
  These data indicate that the Zeiss retinal vessel analyser is an accurate system for the assessment of retinal diameters in healthy subjects. In addition, nitric oxide appears to have a strong influence on retinal vascular tone.
authors.affiliation: Department of Clinical Pharmacology, University of Vienna, Vienna, Austria.
authors.forename: K
authors.initials: K
authors.lastname: Polak
authors.forename: G
authors.initials: G
authors.lastname: Dorner
authors.forename: B
authors.initials: B
authors.lastname: Kiss
authors.forename: E
authors.initials: E
authors.lastname: Polska
authors.forename: O
authors.initials: O
authors.lastname: Findl
authors.forename: G
authors.initials: G
authors.lastname: Rainer
authors.forename: H G
authors.initials: HG
authors.lastname: Eichler
authors.forename: L
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage; D000328:Adult; D018592:Cross-Over Studies; D006801:Humans; D008297:Male; D009599:Nitroprusside / Q000008:administration & dosage; D009885:Ophthalmology / Q000295:instrumentation*; D010656:Phenylephrine / Q000008:administration & dosage; D010919:Placebos; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000008:administration & dosage
chemical_list: D000316:Adrenergic alpha-Agonists; D010919:Placebos; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine