title: Detector sensitivity influences blood flow sampling in scanning laser Doppler flowmetry.
abstract: OBJECTIVE
  To establish the effect of photodiode sensitivity on the DC (brightness) value and the resultant blood flow measurements of retina and rim tissue using a scanning laser Doppler flowmeter (SLDF).
  
  
  METHODS
  The sample consisted of one eye of each of 15 healthy subjects (mean age 27.8 +/- 6.1 years). Using the Heidelberg Retina Flowmeter (HRF), three 10-deg images of the superior temporal retina and three further images of the superior temporal rim were acquired for each of five DC bands: band 1: 30-70; band 2: 70-110; band 3: 110-150; band 4 150-190; band 5: 190-230. Retinal blood volume, flow and velocity were determined for each image using a 10 x 10 pixel square grid located at a predetermined location on the retina and rim for each subject. Following image acquisition, the DC values corresponding to each pre-assigned retinal or rim location were determined. The mean and standard deviation were determined for the blood flow parameters within each DC band for each subject in both locations. Analysis of variance was used to identify significant change in the data as a function of the DC value (P<0.05).
  
  
  RESULTS
  Analysis of variance revealed that retinal blood flow measures acquired within DC band 5 resulted in significantly lower measures of blood flow and velocity (P=0.035 and P=0.049 respectively) than at lower DC values. Band 5 values of flow, volume and velocity in the neuroretinal rim were also significantly low (P=0.016, P= 0.003 and P=0.026 respectively). Peak neuroretinal rim blood flow was recorded when the DC value was between 70 and 110. For blood flow measurement at the retina and neuroretinal rim the DC value should not exceed 190.
  
  
  CONCLUSIONS
  Photodiode sensitivity as indicated by the DC value affects measurements of ocular blood flow using the HRF.
authors.affiliation: Neurosciences Research Institute, Aston University, Aston Triangle, Birmingham, UK. s.l.hosking@aston.ac.uk
authors.forename: S L
authors.initials: SL
authors.lastname: Hosking
authors.forename: S
authors.initials: S
authors.lastname: Embleton
authors.forename: L
authors.initials: L
authors.lastname: Kagemann
authors.forename: A
authors.initials: A
authors.lastname: Chabra
authors.forename: C
authors.initials: C
authors.lastname: Jonescu-Cuypers
authors.forename: A
authors.initials: A
authors.lastname: Harris
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D005260:Female; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008297:Male; D009898:Optic Disk / Q000098:blood supply*; D012171:Retinal Vessels / Q000502:physiology*; D012680:Sensitivity and Specificity