title: Quantifying the pattern of optic tract degeneration in human hemianopia.
abstract: BACKGROUND
  The existence of transsynaptic retrograde degeneration (TRD) in the human visual system has been established, however the dependence of TRD on different factors such as lesion location, size and manner of lesion acquisition has yet to be quantified.
  
  
  METHODS
  We obtained T1-weighted structural and diffusion-weighted images for 26 patients with adult-acquired or congenital hemianopia and 12 age-matched controls. The optic tract (OT) was defined and measured in the structural and diffusion-weighted images, and degeneration assessed by comparing the integrity of tracts in the lesioned and in the undamaged hemisphere.
  
  
  RESULTS
  OT degeneration was found in all patients with established lesions, regardless of lesion location. In patients with acquired lesions, the larger the initial lesion, the greater is the resulting TRD. However, this was not the case for congenital patients, who generally showed greater degeneration than would be predicted by lesion size. A better predictor of TRD was the size of the visual field deficit, which was correlated with degeneration across all patients. Interestingly, although diffusion-weighted imaging (DWI) is more frequently used to examine white matter tracts, in this study the T1-weighted scans gave a better indication of the extent of tract degeneration.
  
  
  CONCLUSIONS
  We conclude that TRD of the OT occurs in acquired and congenital hemianopia, is correlated with visual field loss, and is most severe in congenital cases. Understanding the pattern of TRD may help to predict effects of any visual rehabilitation training.
authors.affiliation: Oxford Centre for functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, , Oxford, UK.
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Millington
authors.forename: Clarissa L
authors.initials: CL
authors.lastname: Yasuda
authors.forename: Panitha
authors.initials: P
authors.lastname: Jindahra
authors.forename: Mark
authors.initials: M
authors.lastname: Jenkinson
authors.forename: John L
authors.initials: JL
authors.lastname: Barbur
authors.forename: Christopher
authors.initials: C
authors.lastname: Kennard
authors.forename: Fernando
authors.initials: F
authors.lastname: Cendes
authors.forename: Gordon T
authors.initials: GT
authors.lastname: Plant
authors.forename: Holly
authors.initials: H
authors.lastname: Bridge
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006423:Hemianopsia / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging; D012183:Retrograde Degeneration / Q000473:pathology*; D058609:Visual Field Tests; D014795:Visual Pathways / Q000473:pathology*
keywords: MRI; STROKE; VISION