Structure-function mapping: variability and conviction in tracing retinal nerve fiber bundles and comparison to a computational model.

PURPOSE: 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.