title: Lens opacity and refractive influences on the measurement of retinal vascular fractal dimension.
abstract: OBJECTIVE
  To examine the influence of lens opacity and refraction on the measurement of retinal vascular fractal dimension (Df).
  
  
  METHODS
  Optic disc photographs (right eyes) of 3654 baseline Blue Mountains Eye Study participants (aged 49-97) were digitized. Retinal vascular Df was quantified using a computer-based program. Summated severity scores for nuclear, cortical and posterior subcapsular (PSC) cataract were assessed from lens photographs. Refraction data were converted to spherical equivalent refraction (SER), as sum spherical plus 0.5 cylinder power. Axial length was measured at 10-year follow-up examinations using an IOL master.
  
  
  RESULTS
  Mean Df of the retinal vasculature was 1.444±0.023 for 2859 eligible participants. Increasing lens opacity scores were associated with significant reduction in Df (β=-0.0030, p<0.0001). Both cortical and PSC cataract involving central lens area were associated with reduced Df, after controlling for confounding factors (p(trend) ≤0.0105). Increasing myopia severity was associated with reduced Df after adjusting for lens opacity scores and other confounders (p(trend) <0.0001). The slope of Df decrease per SER reduction was 0.0040 in eyes with SER≤-4D, compared to -0.0016 in eyes with SER>-4D. For axial length quintiles, there were no significant differences in mean Df in all groups except a reduction in the fifth quintile (axial length ≥24.15mm) (all p<0.05).
  
  
  CONCLUSIONS
  Ocular media opacity independently influenced retinal vascular Df measurement, but we found no evidence supporting any refractive axial magnification effect on this measure. Myopic refraction ≤-4D was associated with a reduction in Df, suggesting rarefaction of retinal vasculature associated with high myopia.
authors.affiliation: Centre for Vision Research, Department of Ophthalmology & Westmead Millennium Institute, University of Sydney, Sydney, NSW, Australia.
authors.forename: Haitao
authors.initials: H
authors.lastname: Li
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
authors.forename: Gerald
authors.initials: G
authors.lastname: Liew
authors.forename: Elena
authors.initials: E
authors.lastname: Rochtchina
authors.forename: Annette
authors.initials: A
authors.lastname: Kifley
authors.forename: Tien Y
authors.initials: TY
authors.lastname: Wong
authors.forename: Wynne
authors.initials: W
authors.lastname: Hsu
authors.forename: Mong L
authors.initials: ML
authors.lastname: Lee
authors.forename: Yong P
authors.initials: YP
authors.lastname: Zhang
authors.forename: Jie J
authors.initials: JJ
authors.lastname: Wang
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D058452:Axial Length, Eye; D002386:Cataract / Q000145:classification / Q000503:physiopathology*; D005260:Female; D017709:Fractals; D006801:Humans; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology*; D009898:Optic Disk; D010781:Photography; D012029:Refraction, Ocular / Q000502:physiology; D012171:Retinal Vessels / Q000473:pathology*