title: Decreased retinal capillary flow is not a mediator of the protective myopia-diabetic retinopathy relationship.
abstract: OBJECTIVE
  The mechanisms supporting the protective relationship between a longer axial length (AL) and a decreased risk of diabetic retinopathy (DR) remain unclear. Previous studies have demonstrated reduced retinal blood flow in axial myopia, and it has been suggested that the compromised retinal capillaries in diabetes are less likely to leak and rupture as a result of this decreased flow. In this study, we therefore investigated if reduced retinal capillary flow (RCF) is a potential mechanism underpinning this protective relationship.
  
  
  METHODS
  Retinal capillary flow was assessed using the Heidelberg Retinal Flowmeter in 150 eyes of 85 patients with diabetes aged 18+ years from the Royal Victorian Eye and Ear Hospital and St. Vincent's Hospital (Melbourne), Australia. Axial length was measured using the Intraocular Lens Master. Diabetic retinopathy was graded from two-field retinal photographs into none, mild, moderate, and severe DR using the modified Airlie House classification system.
  
  
  RESULTS
  A total of 74 out of 150 eyes (49.3%) had DR. A longer AL was associated with decreased odds of DR presence (per mm increase in AL, odds ratio [OR] 0.61, 95% confidence interval [CI] 0.41-0.91) and DR severity (OR: 0.65; 95% CI: 0.44-0.95). However, no association was found between AL and RCF (per mm increase in AL, regression coefficient [β] -1.80, 95% CI -13.50 to 9.50) or between RCF and DR (per unit increase in RCF, OR 1.00; 95% CI 0.99-1.00).
  
  
  CONCLUSIONS
  Our finding suggests that diminished RCF may not be a major factor underlying the protective association between axial elongation and DR.
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
authors.forename: Ryan Eyn Kidd
authors.initials: RE
authors.lastname: Man
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia Department of Ophthalmology, Faculty of Medicine, Gadjah Mada University, Yogyakarta, Indonesia.
authors.forename: Muhammad Bayu
authors.initials: MB
authors.lastname: Sasongko
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
authors.forename: Jing
authors.initials: J
authors.lastname: Xie
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
authors.forename: William J
authors.initials: WJ
authors.lastname: Best
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Noonan
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
authors.forename: Tiffany Ching Shen
authors.initials: TC
authors.lastname: Lo
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia Centre for Vision Research, Westmead Millennium Institute, University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Jie Jin
authors.initials: JJ
authors.lastname: Wang
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
authors.forename: Chi D
authors.initials: CD
authors.lastname: Luu
authors.affiliation: Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, Australia Singapore Eye Research Institute, National University of Singapore, Singapore Duke-NUS Graduate Medical School, Singapore.
authors.forename: Ecosse L
authors.initials: EL
authors.lastname: Lamoureux
mesh_terms: D058452:Axial Length, Eye / Q000503:physiopathology*; D002196:Capillaries / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D003930:Diabetic Retinopathy / Q000150:complications / Q000503:physiopathology*; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000150:complications / Q000503:physiopathology*; D012039:Regional Blood Flow / Q000502:physiology*; D012171:Retinal Vessels / Q000503:physiopathology*; D012212:Rheology / Q000379:methods; D012720:Severity of Illness Index
keywords: axial length; diabetic retinopathy; myopia; retinal blood flow; retinal capillary flow