title: Strategies for reducing variance in laser Doppler flowmetry measurements.
abstract: BACKGROUND
  Scattering of blood flow data as assessed with laser Doppler flowmetry (LDF) in humans is a problem in many studies using this technique. We set out to reduce variability in LDF data by eliminating the effect of the total returning light level (DC) on LDF parameters in the choroid through partial regression analysis.
  
  
  METHODS
  In 20 healthy subjects, choroidal blood flow parameters were measured at different DC values using a portable confocal LDF device. We used two different strategies to reduce scattering of data eliminating the effect of yield, which is defined as DC/gain. On the one hand, we used a previously described method based on a third-order polynomial fit, which combines all obtained data. On the other hand, we applied a new method based on a linear fit for each individual subject.
  
  
  RESULTS
  Variability of data during changes in DC is higher for LDF parameters volume and flow than for velocity. Both methods were successful in reducing scattering of LDF parameters with varying DC.
  
  
  CONCLUSIONS
  The present study indicates that both methods to correct for changes in yield were successful in reducing the variability of LDF measurements. When systematic changes in DC occur after an intervention, one needs to be careful in interpreting the obtained data and it remains to be shown if either of the two techniques is capable of correcting for this effect. The approach presented here may, however, represent an effective, easily applicable and valid approach to reduce scattering of data from using LDF to assess blood flow in the posterior pole of the human eye.
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria.
authors.forename: Berthold
authors.initials: B
authors.lastname: Pemp
authors.forename: Noemi
authors.initials: N
authors.lastname: Maar
authors.forename: Guenther
authors.initials: G
authors.lastname: Weigert
authors.forename: Alexandra
authors.initials: A
authors.lastname: Luksch
authors.forename: Hemma
authors.initials: H
authors.lastname: Resch
authors.forename: Gerhard
authors.initials: G
authors.lastname: Garhofer
authors.forename: Selim
authors.initials: S
authors.lastname: Orgul
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000328:Adult; D001794:Blood Pressure; D002829:Choroid / Q000098:blood supply* / Q000000981:diagnostic imaging*; D003941:Diagnostic Techniques, Ophthalmological / Q000592:standards*; D005260:Female; D006339:Heart Rate; D006801:Humans; D007429:Intraocular Pressure; D017078:Laser-Doppler Flowmetry / Q000592:standards*; D016014:Linear Models; D008297:Male; D009898:Optic Disk / Q000098:blood supply* / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D014463:Ultrasonography; D055815:Young Adult
references.citation: Graefes Arch Clin Exp Ophthalmol. 1997 Oct;235(10):618-26
references.pmid: 9349945
references.citation: Invest Ophthalmol Vis Sci. 2002 Mar;43(3):723-8
references.pmid: 11867590
references.citation: J Biomed Opt. 1999 Oct;4(4):459-64
references.pmid: 23014619
references.citation: Int Ophthalmol. 2001;23(4-6):183-9
references.pmid: 11944839
references.citation: J Glaucoma. 1996 Apr;5(2):99-105
references.pmid: 8795741
references.citation: Vis Neurosci. 1996 Jul-Aug;13(4):655-69
references.pmid: 8870223
references.citation: Invest Ophthalmol Vis Sci. 1994 Dec;35(13):4273-81
references.pmid: 8002247
references.citation: Invest Ophthalmol Vis Sci. 1995 Mar;36(3):579-85
references.pmid: 7890489
references.citation: Invest Ophthalmol Vis Sci. 2000 Aug;41(9):2678-83
references.pmid: 10937582
references.citation: Curr Eye Res. 2000 Aug;21(2):669-76
references.pmid: 11148604
references.citation: Exp Eye Res. 1992 Sep;55(3):499-506
references.pmid: 1426079
references.citation: Exp Eye Res. 1994 May;58(5):529-43
references.pmid: 7925690
references.citation: Invest Ophthalmol Vis Sci. 1998 Mar;39(3):559-64
references.pmid: 9501867
references.citation: Graefes Arch Clin Exp Ophthalmol. 2001 Jul;239(6):407-10
references.pmid: 11561787