title: Reproducibility of color Doppler imaging.
abstract: OBJECTIVE
  The aims of this study were: (1) to determine the intra-subject and inter-observer variability of color Doppler imaging (CDI) measurements and readings of the retrobulbar blood vessels, (2) to compare the difference invariability of CDI parameters in non-glaucomatous controls versus glaucoma patients, and (3) to provide calculations of minimum sample sizes for future CDI studies.
  
  
  METHODS
  Patients with normal tension glaucoma (n=28), primary open-angle glaucoma (n=19) and non-glaucomatous controls of comparable age (n=22) underwent CDI on two occasions 1 month apart. Variability in CDI parameters was quantified using (within-subject) coefficients of variation. Based on this variability, minimum sample sizes were calculated to guide the design of future studies comparing CDI between and within groups.
  
  
  RESULTS
  In general, within-subject coefficients of variation for measurements 1 month apart were comparable to previously reported short-term variations. Variability was higher in glaucoma patients than in non-glaucomatous controls. The minimum sample size required for glaucomatous study populations is larger than for non-glaucomatous controls. Smaller patient groups are required to detect change using the peak systolic blood flow velocities than using end diastolic velocities. Studies using a cross-over design require smaller sample sizes than studies with a prepost or particularly parallel design.
  
  
  CONCLUSIONS
  This study provides extensive information on long-term intra-subject variability of CDI measurements in non-glaucomatous controls as well as glaucoma patients. Moreover, sample size calculations are provided for studies involving glaucoma patients as well as non-glaucomatous individuals, using three different commonly used study designs.
authors.affiliation: Department of Ophthalmology, University Hospitals Leuven, Campus St Raphaël, Leuven, Belgium. ingeborg.stalmans@uzleuven.be
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Stalmans
authors.forename: Brent
authors.initials: B
authors.lastname: Siesky
authors.forename: Thierry
authors.initials: T
authors.lastname: Zeyen
authors.forename: Steffen
authors.initials: S
authors.lastname: Fieuws
authors.forename: Alon
authors.initials: A
authors.lastname: Harris
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001783:Blood Flow Velocity; D001794:Blood Pressure; D019842:Ciliary Arteries / Q000502:physiology*; D005902:Glaucoma, Open-Angle / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure; D008875:Middle Aged; D015588:Observer Variation; D009880:Ophthalmic Artery / Q000502:physiology*; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D012161:Retinal Artery / Q000502:physiology*; D014065:Tonometry, Ocular; D018615:Ultrasonography, Doppler, Color