title: Diffusion coefficient through the blood-aqueous barrier using a standard protocol.
abstract: OBJECTIVE
  Comparison of the diffusion coefficient through the blood-aqueous barrier of healthy volunteers measured in different cities with identical fluorophotometers using a standardised protocol.
  
  
  METHODS
  Healthy volunteers aged between 20 and 70 years were studied in seven European cities. The fluorescein concentration in the anterior segment of each eye was measured with a commercial scanning fluorophotometer 30 and 40 minutes after intravenous fluorescein. The decay of non-protein bound fluorescein concentration in blood plasma was determined with the use of three blood samples taken at 7, 15, and 55 minutes after injection. The diffusion coefficient through the blood-aqueous barrier was calculated from the ratio between the fluorescein concentration in the anterior chamber and the time integral of non-protein bound fluorescein concentration in plasma using specially developed software.
  
  
  RESULTS
  The mean values of the diffusion coefficient (SD) (X10(-4) min-1) were 4.76 (1.51) (n = 20, Brussels), 5.48 (2.33) (n = 17, Coimbra), 3.47 (2.09) (n = 12, Cologne), 6.09 (2.77) (n = 21, Frankfurt), 3.85 (1.59) (n = 11, Ghent), 4.99 (1.69) (n = 23, Leiden), and 4.87 (1.05) (n = 20, Madrid). The values between centres were similar (Kruskal-Wallis test p > 0.05) except for Cologne and Frankfurt (p = 0.013). No differences were found when repeating measurements (four centres, interval time 1-8 months, Wilcoxon paired test p > 0.39).
  
  
  CONCLUSIONS
  The diffusion coefficients had similar values and standard deviations. The concerted action demonstrated the usefulness of a standardised protocol.
authors.affiliation: Department of Ophthalmology, Leiden University Hospital, Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: van Best
authors.forename: J B
authors.initials: JB
authors.lastname: del Castillo
authors.forename: M
authors.initials: M
authors.lastname: Diestelhorst
authors.forename: B
authors.initials: B
authors.lastname: Heintz
authors.forename: E
authors.initials: E
authors.lastname: Leite
authors.forename: L F
authors.initials: LF
authors.lastname: Liesenborghs
authors.forename: R
authors.initials: R
authors.lastname: Schalnus
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001692:Biological Transport / Q000502:physiology; D018916:Blood-Aqueous Barrier / Q000502:physiology*; D016022:Case-Control Studies; D003922:Diabetes Mellitus, Type 1 / Q000150:complications; D005240:Feasibility Studies; D005260:Female; D019793:Fluorescein; D005452:Fluoresceins / Q000493:pharmacokinetics*; D015590:Fluorophotometry / Q000379:methods*; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results
chemical_list: D005452:Fluoresceins; D019793:Fluorescein