title: The retinal vasculature as a fractal: methodology, reliability, and relationship to blood pressure.
abstract: OBJECTIVE
  Fractals represent a type of derived geometric pattern that permits the characterization of the branching pattern of retinal vessels. We examined a new semiautomated method to measure retinal vessel fractals.
  
  
  METHODS
  Methodology study.
  
  
  METHODS
  Three hundred randomly selected participants from the population-based Blue Mountains Eye Study.
  
  
  METHODS
  We developed a semiautomated computer program to measure the fractal dimension (D(f)) of the retinal vessels from digitized images of disk-centered retinal photographs. Two trained graders masked to participant characteristics measured D(f) of right eye images of participants. Reliability was determined by repeat grading of the images from 60 participants, and association with systolic and diastolic blood pressure was examined in all 300 participants.
  
  
  METHODS
  D(f) of the retinal vessels.
  
  
  RESULTS
  Mean D(f) was 1.437 with a standard deviation of 0.025. Intragrader and intergrader reliability estimates were high with intraclass correlation ranging from 0.93 to 0.95. D(f) was inversely correlated with age (r = -0.42, P = 0.001) and systolic blood pressure (r = -0.29, P<0.0001). After adjustment for age and sex, mean D(f) was significantly lower in participants with than without hypertension (D(f) difference 0.01, P = 0.02).
  
  
  CONCLUSIONS
  The D(f) of the retinal vessels can be reliably measured from photographs and shows a strong inverse correlation with blood pressure. These data suggest that the D(f) may be a measure of early microvascular alterations from elevated blood pressure. Further studies to examine the systemic and ocular correlates of the D(f) of the retinal vessels are needed.
authors.affiliation: Centre for Vision Research, University of Sydney, Australia.
authors.forename: Gerald
authors.initials: G
authors.lastname: Liew
authors.forename: Jie Jin
authors.initials: JJ
authors.lastname: Wang
authors.forename: Ning
authors.initials: N
authors.lastname: Cheung
authors.forename: Yong Ping
authors.initials: YP
authors.lastname: Zhang
authors.forename: Wynne
authors.initials: W
authors.lastname: Hsu
authors.forename: Mong Li
authors.initials: ML
authors.lastname: Lee
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
authors.forename: Gabriella
authors.initials: G
authors.lastname: Tikellis
authors.forename: Bronwen
authors.initials: B
authors.lastname: Taylor
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D017709:Fractals; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010781:Photography; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000033:anatomy & histology*