title: Impact of simulated light scatter on scanning laser Doppler flowmetry.
abstract: OBJECTIVE
  To determine the impact of simulated light scatter on scanning laser Doppler flowmetry (SLDF) assessment of retinal capillary blood flow and retinal image quality.
  
  
  METHODS
  One eye of 10 normal subjects (mean (SD) age 24 (1.7) years, range 22-27) was randomly selected. Varying concentrations of polystyrene microspheres were suspended in optically clear cells to simulate light scatter. The microsphere concentrations used were 0.05%, 0.03%, 0.02%, 0.01%, and a cell containing only water. LogMAR visual acuity and contrast sensitivity were measured both with and without cells. Optimal focus and alignment was established by acquiring three SLDF images each of the optic nerve head (ONH) and of the macula using the Heidelberg retina flowmeter (HRF) with no cell in place. SLDF images were subsequently acquired with each of the light scatter cells mounted in front of the HRF. The group mean retinal capillary blood flow was compared using repeated measures analysis of variance (reANOVA) as a function of microsphere concentration.
  
  
  RESULTS
  Retinal capillary blood flow increased significantly in the ONH, nasal macula, fovea, and temporal macula with increasing microsphere concentration (p<0.0001). Using Dunnett's post hoc test, retinal capillary blood flow was found to be significantly increased relative to the no cell condition for the 0.03% and 0.05% cell concentrations.
  
  
  CONCLUSIONS
  Simulated light scatter produces an artifactual increase in retinal capillary blood flow. The impact of cataract on SLDF measurements has yet to be determined.
authors.affiliation: Multi-Disciplinary Laboratory for the Research of Sight-Threatening Diabetic Retinopathy, School of Optometry, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada.
authors.forename: S T
authors.initials: ST
authors.lastname: Venkataraman
authors.forename: C
authors.initials: C
authors.lastname: Hudson
authors.forename: E
authors.initials: E
authors.lastname: Harvey
authors.forename: J G
authors.initials: JG
authors.lastname: Flanagan
mesh_terms: D000328:Adult; D002196:Capillaries; D002386:Cataract / Q000503:physiopathology; D015350:Contrast Sensitivity; D005260:Female; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000592:standards*; D008027:Light; D008297:Male; D008863:Microspheres; D010316:Particle Size; D012039:Regional Blood Flow; D012160:Retina / Q000502:physiology*; D012171:Retinal Vessels; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D014792:Visual Acuity