title: Structure-function mapping: variability and conviction in tracing retinal nerve fiber bundles and comparison to a computational model.
abstract: OBJECTIVE
  We evaluated variability and conviction in tracing paths of retinal nerve fiber bundles (RNFBs) in retinal images, and compared traced paths to a computational model that produces anatomically-customized structure-function maps.
  
  
  METHODS
  Ten retinal images were overlaid with 24-2 visual field locations. Eight clinicians and 6 naïve observers traced RNFBs from each location to the optic nerve head (ONH), recording their best estimate and certain range of insertion. Three clinicians and 2 naïve observers traced RNFBs in 3 images, 3 times, 7 to 19 days apart. The model predicted 10° ONH sectors relating to each location. Variability and repeatability in best estimates, certain range width, and differences between best estimates and model-predictions were evaluated.
  
  
  RESULTS
  Median between-observer variability in best estimates was 27° (interquartile range [IQR] 20°-38°) for clinicians and 33° (IQR 22°-50°) for naïve observers. Median certain range width was 30° (IQR 14°-45°) for clinicians and 75° (IQR 45°-180°) for naïve observers. Median repeatability was 10° (IQR 5°-20°) for clinicians and 15° (IQR 10°-29°) for naïve observers. All measures were worse further from the ONH. Systematic differences between model predictions and best estimates were negligible; median absolute differences were 17° (IQR 9°-30°) for clinicians and 20° (IQR 10°-36°) for naïve observers. Larger departures from the model coincided with greater variability in tracing.
  
  
  CONCLUSIONS
  Concordance between the model and RNFB tracing was good, and greatest where tracing variability was lowest. When RNFB tracing is used for structure-function mapping, variability should be considered.
authors.affiliation: Optometry and Vision Sciences, The University of Melbourne, Melbourne, Australia.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Denniss
authors.forename: Andrew
authors.initials: A
authors.lastname: Turpin
authors.forename: Fumi
authors.initials: F
authors.lastname: Tanabe
authors.forename: Chota
authors.initials: C
authors.lastname: Matsumoto
authors.forename: Allison M
authors.initials: AM
authors.lastname: McKendrick
mesh_terms: D003198:Computer Simulation; D006801:Humans; D009412:Nerve Fibers; D009434:Neural Pathways / Q000502:physiology; D056347:Neuroanatomical Tract-Tracing Techniques; D009887:Ophthalmoscopy; D009898:Optic Disk / Q000033:anatomy & histology*; D010781:Photography; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000166:cytology*; D014794:Visual Fields / Q000502:physiology*
keywords: glaucoma; mapping; optic nerve head; structure–function; visual field