Stabilization and comparison of TOP and Bracketing perimetric strategies using a threshold spatial filter

Abstract

To evaluate a new perimetric spatial filter that takes into account relations of dependence between regions of the glaucomatous visual field. 51 glaucoma patients and 30 controls were examined using the Octopus 1-2-3 on four occasions using program 32; two with TOP and two with Bracketing (BRA) strategy. Each threshold was replaced by a filtered threshold, calculated as the mean of its own value and the four points best correlated with it, weighted with the correlation coefficient (r) that relates them. Application of the filter had minimal effect on the absolute mean defect (MD) but reduced the square root of loss variance (sLV) by 17.6% in TOP and 28.8% in BRA, increasing the similarity between their results. Filtered TOP and BRA thresholds were more similar than those obtained in the two unfiltered BRA examinations. Filtering reduced the value of short fluctuation by 28.6% in TOP and 45.4% in BRA and reduced sLV fluctuation by 14.3% in TOP and 24.2% in BRA, thus harmonizing the two strategies for these two parameters (p > 0.05). The influence of filtering on MD fluctuation was minimal (p > 0.05). In normal subjects the number of points beyond 5 dB of normality (not reproducible false scotomas) reduced from 1.5% to 0.2% in TOP and from 4.9% to 1.6% in BRA, while in glaucoma patients changes were minimal. The proposed spatial filter stabilized perimetric results, acting with greater effect on BRA than on TOP, making their results more similar.