title: Axial length, retinal function, and oxygen consumption: a potential mechanism for a lower risk of diabetic retinopathy in longer eyes.
abstract: OBJECTIVE
  To determine the relationship between axial length (AL), retinal function, and relative oxygen (O₂) consumption to better understand the protective effect of axial elongation on diabetic retinopathy development.
  
  
  METHODS
  Measurements of AL, multifocal electroretinogram (mfERG), and relative O₂ consumption (difference between arteriolar and venular O₂ saturation levels or A-V difference) were performed on 50 healthy individuals. The relationships between AL, mfERG amplitude, and A-V difference were analyzed using linear regression models. Path analysis was performed to determine the direct and indirect effects (via mfERG amplitude) of AL on A-V difference.
  
  
  RESULTS
  mfERG P1 amplitude was positively associated with A-V difference (β = 0.33; 95% confidence interval [CI]: 0.23-0.42). Increased AL was significantly associated with a decrease in A-V difference (β = -1.08; 95% CI: -1.52 to -0.65) as well as a decrease in retinal function (β = -3.14, 95% CI: -4.07 to -2.20). Path analysis models including AL (study factor), retinal function (intermediate variable), and A-V difference (outcome variable) showed that AL had little direct association with A-V difference (β(p) = -0.002), while the indirect effect of AL on A-V difference via changes in retinal function were substantial (β(p) = -0.51).
  
  
  CONCLUSIONS
  In eyes with longer AL, the reduction in A-V difference is explained by the parallel reduction in retinal function. These findings suggest that longer eyes have decreased retinal function and O₂ consumption, and thus are relatively less hypoxic in the presence of diabetes, which may partly explain the reduced risk of DR in these eyes.
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.forename: Ecosse L
authors.initials: EL
authors.lastname: Lamoureux
authors.forename: Yamna
authors.initials: Y
authors.lastname: Taouk
authors.forename: Jing
authors.initials: J
authors.lastname: Xie
authors.forename: Muhammad Bayu
authors.initials: MB
authors.lastname: Sasongko
authors.forename: William J
authors.initials: WJ
authors.lastname: Best
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Noonan
authors.forename: Ryo
authors.initials: R
authors.lastname: Kawasaki
authors.forename: Jie Jin
authors.initials: JJ
authors.lastname: Wang
authors.forename: Chi D
authors.initials: CD
authors.lastname: Luu
mesh_terms: D000293:Adolescent; D000328:Adult; D058452:Axial Length, Eye / Q000503:physiopathology*; D001786:Blood Glucose / Q000378:metabolism; D003930:Diabetic Retinopathy / Q000503:physiopathology*; D004596:Electroretinography; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism; D006801:Humans; D008055:Lipids / Q000097:blood; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D012160:Retina / Q000503:physiopathology*; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin; D008055:Lipids; C517652:hemoglobin A1c protein, human
keywords: axial length; diabetic retinopathy; electroretinogram; myopia; oximetry; oxygen consumption; retinal function