Purpose Goldmann visual fields (GVFs) are useful for tracking changes in areas of functional retina, including the periphery, in inherited retinal degeneration patients. Quantitative GVF analysis requires digitization of the chart coordinates for the main axes and isopter points marked by the GVF operator during testing. This study investigated inter- and intra-digitizer variability among users of a manual GVF digitization program. Methods Ten digitizers were trained for one hour, then digitized 23 different GVFs from inherited retinal degeneration patients in each of three testing blocks. Digitizers labeled each isopter as seeing or non-seeing, and its target size. Isopters with the same test target within each GVF were grouped to create isopter groups. Results The standard deviation of isopter group area showed an approximate square-root relationship with total isopter group area. Accordingly, the coefficient of variation for isopter group area decreased from 68% to 0.2% with increasing isopter group area. A bootstrap version of ANOVA did not reveal a significant effect of digitizers on isopter group area. Simulations involving random sampling of digitizers showed that 5–7 digitizers would be required to catch 95–99% of labeling errors and isopter misses, on the basis of data discrepancies, with 99% probability. Conclusions These data suggest that any minimally trained digitizer would be capable of reliably determining any isopter area, regardless of size. Studies using this software could either use 5–7 minimally trained digitizers for each GVF, three digitizers who demonstrate low frequencies of errors on a practice set of GVFs, or two digitizers with an expert reader to adjudicate discrepancies and catch errors.
A digitized waveform is approximated by segments whose total description length is minimal for a given error bound. This approximation can be computed efficiently, and can be used for segmentation. The method is also shown to be applicable for segmentation and edge detection in gray level and range images.
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