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Comparative study between pointwise and ranked threshold distribution analyses of change in serial fields for
1Glaucoma Center and Visual Function Laboratory, University of California at San Diego, La Jolla, USA.
Purpose:
To assess the validity of ranked threshold distribution (RTD) analysis for longitudinal evaluation of short-wavelength automated perimetry (SWAP).
Methods:
Eighty-five patients with glaucoma and with three or more SWAP results were examined. An additional 20 patients with glaucoma and 3 stable standard automated visual fields and 3 stable SWAP fields were assessed to calculate variability. An RTD curve was created. For RTD analysis and pointwise analysis, values that decreased more than the SWAP variability were considered to have worsened. Using pointwise analysis, four groups were defined: no change (without any 2 contiguous points decreasing in threshold); focal change (at least 2 contiguous points with decreased thresholds in either hemifield); diffuse change (more than 50% of the entire 52 locations with significant decrease in thresholds); and focal and diffuse change (less than 50%, but crossing both hemifields).
Results:
Using pointwise analysis, 32 (37.6%) patients did not change; 23 (27.1%) patients had focal worsening; 8 (9.4%) patients had diffuse worsening; and 22 (25.9%) patients had focal and diffuse worsening. Significant differences were found among the groups in the number of deteriorating locations (P < 0.0001, analysis of variance). The ranges of deteriorating locations identified by RTD analysis for focal change and diffuse change did not overlap. A significant correlation was found between the numbers of locations with decreased threshold by both analyzes (r2 = 0.83, P < 0.0001).
Conclusion:
For evaluation of possible SWAP progression, RTD analysis is closely related with pointwise analysis and is useful for visualizing a diffuse component of change in the field.