title: Vascular Changes and Neurodegeneration in the Early Stages of Diabetic Retinopathy: Which Comes First?
abstract: BACKGROUND
  Neurodegeneration is an early component of diabetic retinopathy (DR). It is unclear whether neurodegeneration is an independent factor or a consequence of damaged retinal vasculature. The aims of this study were to review the literature concerning neurodegeneration in diabetic patients without or with early DR, and to examine whether neurodegeneration precedes visible vasculopathy in the pathogenesis of DR.
  
  
  METHODS
  A systematic literature search was performed to identify studies which used optical coherence tomography (OCT) or multifocal electroretinography (mfERG) to detect neurodegeneration in patients with no or mild DR as compared to healthy controls. Outcome measures were mean retinal thickness (RT), mean retinal nerve fiber layer (RNFL) thickness and ganglion cell layer (GCL) thickness. Also, mfERG amplitude and implicit time were analyzed.
  
  
  RESULTS
  Eleven studies which used mfERG and/or OCT to detect neurodegeneration were included. Two OCT studies found significant thinning of RT, 2 found thinning of RNFL, whereas 1 found thickening of RT, RNFL and GCL in patients without DR. Two mfERG studies found a significant delay of implicit time in the same patient group. Retinal thinning and delay of implicit time were also detected in patients with mild DR.
  
  
  CONCLUSIONS
  Retinal neurodegeneration is an early component of DR, which can precede visible vasculopathy.
authors.affiliation: Research Unit of Ophthalmology, Institute of Clinical Research, University of Southern Denmark, Odense, Denmark.
authors.forename: Karoline Boegeberg
authors.initials: KB
authors.lastname: Jonsson
authors.forename: Ulrik
authors.initials: U
authors.lastname: Frydkjaer-Olsen
authors.forename: Jakob
authors.initials: J
authors.lastname: Grauslund
mesh_terms: D003930:Diabetic Retinopathy / Q000150:complications / Q000175:diagnosis*; D004596:Electroretinography; D006801:Humans; D009412:Nerve Fibers / Q000473:pathology*; D012162:Retinal Degeneration / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D012165:Retinal Ganglion Cells / Q000473:pathology*; D012171:Retinal Vessels / Q000473:pathology*; D041623:Tomography, Optical Coherence / Q000379:methods*